TR Technical Report. What requirements does the KBS-3 repository make on the host rock?

Transcription

1 Technical Report TR What requirements does KBS-3 repository make on host rock? Geoscientific suitability indicators criteria for siting site evaluation Johan Andersson Golder Grundteknik Anders Ström, Christer Svemar Svensk Kärnbränslehantering AB Karl-Erik Almén KEA Geo-Konsult AB Lars O Ericsson Chalmers University Technology April 2000 Svensk Kärnbränslehantering AB Swedish Nuclear Fuel Waste Management Co Box 5864 SE Stockholm Sweden Tel Fax

2 What requirements does KBS-3 repository make on host rock? Geoscientific suitability indicators criteria for siting site evaluation Johan Andersson Golder Grundteknik Anders Ström, Christer Svemar Svensk Kärnbränslehantering AB Karl-Erik Almén KEA Geo-Konsult AB Lars O Ericsson Chalmers University Technology April 2000 Keywords: deep repository, spent nuclear fuel, geoscientific suitability indicators, criteria, long-term safety, safety assessment, design, site investigations. 1

3 Foreword This report gives an account what requirements are made by deep repository on rock what requirements can be used for siting evaluation sites in conjunction with site investigations. The work was initiated in 1997 an interim report was submitted in conjunction with RD&D-Programme 98 /SKB, 1998/. The work is an important part SKB s preparations for execution site investigations. The report conveys SKB s stpoint in se matters, based on facts presented. The project has been carried out during a period just under three years by a group consisting Karl-Erik Almén, Christer Svemar, Lars O Ericsson, Johan Andersson undersigned. A reference group with following composition was also connected to project: Kaj Ahlbom, Siting, SKB Karin Andersson, Technical Environmental Planning, Chalmers University Technology Stefan Claesson, Isotope Laboratory, Swedish Museum Natural History Allan Hedin, Safety Assessment, SKB Pär Olsson, Skanska The reference group has provided valuable contributions to final report. It should also be mentioned that experts within disciplines geology, rock mechanics, geohydrology, chemistry, rmal properties transport properties rock have gared on a number occasions during course work to augment knowledge bank on which this report ultimately rests. Anders Ström Project Manager Repository Technology Unit SKB 3

4 Summary This report gives an account what requirements are made on rock, what conditions in rock are advantageous (preferences) how fulfilment requirements preferences (criteria) is to be judged prior to selection sites for a site investigation during a site investigation. The conclusions results report are based on knowledge experience acquired by SKB over many years research development. The knowledge gained during SKB s most recent safety assessment, SR 97, is particularly drawn on. The reported requirements, preferences criteria will be used in SKB s continued work with site selection site investigations. The results, particularly stipulated criteria, apply to a repository for spent fuel KBS-3 type, i.e. a repository where fuel is contained in copper canisters embedded in bentonite clay at a depth m in Swedish crystalline basement. If repository concept is changed or if new technical/ scientific advances are made, certain requirements, preferences or criteria may need to be adjusted. Therefore, it should be emphasized that work cannot be used as a basis for siting or types repositories or in or geological settings. The formulations requirements are governed by Swedish laws regulations. To achieve a safe final repository, SKB has developed a final repository concept (KBS-3) based on fundamental safety functions isolation retardation. These functions are influenced by design construction facility engineered barriers, by site-specific conditions on repository site. A number general requirements preferences can also be formulated for facility construction. The report analyzes how rock s different geological conditions, mechanical properties, rmal properties, hydrogeological properties, chemical properties transport properties influence functions deep repository, wher it is possible to determine requirements preferences regarding influence se properties. Where possible, se requirements or preferences have n been translated into requirements or preferences regarding individual properties (parameters). Parameters that can be used to determine wher requirements or preferences are satisfied are called geoscientific suitability indicators. In order to be able to determine at different stages during a site investigation wher requirements preferences for a given parameter are satisfied, criteria are formulated that are based on quantities that can be measured or estimated at relevant stage investigation. 5

5 Generally, terms such as siting factor criteria are ten used without any precise definition. The following definitions apply in this study: Term Function Parameter Requirement Preference Geoscientific suitability indicators Criteria for evaluation Definition Purpose which deep repository is intended to serve, for example to have an isolating retarding function. Physical or chemical quantity (property, condition in rock). Condition that must be satisfied, refers to actual conditions regardless siting stage. All requirements must be satisfied. Condition that ought to be satisfied regardless siting stage. All preferences do not have to be satisfied, however. Measurable or estimable site-specific parameters that can be used in a given siting stage to assess wher requirements preferences are satisfied. Values for suitability indicators in a given siting stage that are decisive for site assessment wher a site satisfies stipulated requirements preferences. What requirements do we make on rock? Numerous conditions need to be determined in a site investigation in order to build up a fundamental understing site. But only certain conditions are direct importance for wher site is suitable for a repository or layout repository on investigated site. The following requirements are made on rock or placement deep repository in rock: The rock in repository s deposition zone may not have any ore potential, i.e. may not contain such valuable minerals that it might justify mining at hundreds metres depth. Regional plastic shear zones shall be avoided if it cannot be demonstrated that properties zone do not deviate from those rest rock. There may, however, be so-called tectonic lenses near regional plastic shear zones where bedrock is homogeneous relatively unaffected. It must be possible to position repository with respect to fracture zones on site. Deposition tunnels deposition holes for canisters may not pass through or be positioned too close to major regional major local fracture zones. Deposition holes may not intersect identified local minor fracture zones. The rock s strength, fracture geometry initial stresses may not be such that large stability problems may arise around tunnels or deposition holes within deposition area. This is checked by means a mechanical analysis, where input values comprise geometry tunnels, strength deformation properties intact rock, geometry fracture system initial rock stresses. The groundwater at repository level may not contain dissolved oxygen. Absence oxygen is indicated by a negative Eh, occurrence Fe(II), or occurrence sulphide. The total salinity (TDS = Total Dissolved Solids) in groundwater must be less than 100 g/l at repository level. 6

6 In addition to above requirements, re are a large number preferences, i.e. conditions that are desirable should be taken into account when positioning repository in rock: Since it can be difficult to predict how different rocks minerals will be used in future, it is preferable to site deep repository in commonly occurring rock types. Moderate density (fracture surface area per volume) local minor fracture zones is preferable, along with moderate density fractures. It is generally an advantage if initial rock stresses at planned repository depth do not deviate from what is normal in Swedish crystalline bedrock. It is preferable that strength deformation properties intact rock be normal for Swedish bedrock, since experience has shown it is possible to carry out rock works with good results in such bedrock. It is preferable that coefficient rmal expansion have normal values for Swedish bedrock (i.e. within range 10 6 to 10 5 K 1 ) that it not differ markedly between rock types in repository area. The rock should have a higher rmal conductivity than 2.5 W/(m,K). Areas with a high potential for geormal energy extraction should be avoided. The undisturbed temperature at repository depth should be less than 25ºC. It is an advantage if a large part rock mass in deposition zone has a hydraulic conductivity (K) that is less than 10 8 m/s. Fracture zones that need to be passed during construction should have such low permeability that y can be passed without problems, which means zones should have a transmissivity (T) that is lower than 10 5 m 2 /s are furrmore not problematical from a construction-related viewpoint. It is an advantage if local hydraulic gradient is lower than 1% at repository level, but lower values do not provide any additional advantage. Undisturbed groundwater at repository level should have a ph in range 6 10, a low concentration organic compounds ([DOC]<20mg/l), low colloid concentration (lower than 0.5 mg/l), low ammonium concentrations, some content calcium magnesium ([Ca 2+ ]+[Mg 2+ ]>4 mg/l) low concentrations radon radium. It is preferable that it be possible to find canister positions in a large fraction rock that have a Darcy velocity lower than 0.01 m/y on a canister hole scale, since lower fluxes increase retardation important radionuclides. It is preferable that a substantial retardation important radionuclides take place in geosphere. A quantitative preference can be expressed in form transport resistance (F parameter), where Darcy velocity, flow distribution flow-wetted surface area per volume rock (or equivalent parameter) are such that a large fraction all flow paths have F greater than 10 4 y/m. It is desirable that matrix diffusivity matrix porosity not be much lower (by a factor 100 or more) than value ranges analyzed in safety assessment SR 97. The accessible diffusion depth should at least exceed a centimetre or so. Areas where biological diversity or species worth protecting may be threatened areas which are or may be important water sources, soil sources or farml should be avoided for deep repository s surface facilities. (Areas protected by law are avoided.) 7

7 As a general rule, satisfied preferences lead to greater safety margins, lower costs, simpler investigations or simpler construction repository. All preferences do not have to be satisfied for a site to be approved for a deep repository. It may very well be so that poorer values for certain parameters are compensated for by better values for ors. An integrated safety assessment a construction analysis are refore always needed to assess safety performance. In addition to above preferences that have directly to do with properties rock, re are preferences that facilitate characterization site. In particular: It is preferable that re be a high proportion exposed rock orwise moderate soil depth (preferably less than about 10 m), since this facilitates determination lithological geological-structural conditions in underlying bedrock from ground surface. It is preferable that bedrock be homogeneous with few rock types regular fracturing, although a small-scale variation in mineral composition, such as in a gneiss, is no disadvantage. Even though requirements preferences have been formulated on basis different safety construction viewpoints, re is scarcely any example a conflict between different requirements or preferences. As a rule, conditions that lead to good long-term safety are also advantageous from construction viewpoint. Selection areas for site investigations Requirements preferences regarding rock should course be used as far as possible to formulate criteria for selection sites for site investigations. Good knowledge conditions on ground surface usually exists after completion a feasibility study, while knowledge conditions in deep rock is very limited. Criteria can refore normally only be formulated for following suitability indicators: After completion a feasibility study, continued studies investigations are only conducted areas that are not deemed to have a potential for occurrence ore or valuable industrial minerals that are deemed to be homogeneous to consist commonly occurring rock types. During feasibility study, study site is selected adapted so that a deep repository can be positioned with good margin in relation to regional plastic shear zones regional fracture zones interpreted in feasibility study. Areas protected by law are avoided, areas for furr investigations are chosen so that y have few conflicting interests (for example a water source) so that surface portion can be adapted with little impact on near-surface ecosystem. Areas with an unsuitably high topographical gradient on a regional scale (greater than 1%) are rejected. The feasibility studies thus identify areas with a good potential to have suitable conditions. But site investigations (from boreholes) are necessary to check this. At same time, report s survey generic knowledge Swedish crystalline bedrock shows that good prospects should exist to find sites in Sweden that satisfy all requirements most essential preferences. 8

8 Under what circumstances should site investigation be discontinued? An overall safety assessment an overall construction analysis comprise essential background material in an integrated assessment wher a site is suitable. The site is only accepted if it is possible to show in safety assessment that a safe deep repository can be constructed. During a site investigation, when measurement data have been obtained from repository depth but before overall assessment has been carried out, criteria are used to check wher above requirements preferences may be satisfied. The criteria provide guidance on outcome assessments can refore also be used to review a safety assessment. The following criteria are so important that site investigation should be discontinued anor site chosen if y cannot be met: If large deposits ore-bearing minerals or valuable industrial minerals are encountered within repository area, site should be aboned. During site investigation, repository is adapted more precisely to nidentified fracture zones. Suitable respect distances to major identified regional local major fracture zones can only be determined site-specifically, but it is assumed that a distance at least several tens metres to major local zones at least 100 metres to regional zones is appropriate. If repository cannot be positioned in a reasonable manner (if it would have to be split up into a very large number parts) in relation to regional plastic shear zones, regional fracture zones or local major fracture zones, site is not suitable for a deep repository. If repository cannot be reasonably configured in such a way that extensive general stability problems can be avoided, site is unsuitable should be aboned. Extensive problems with core discing drill cores should give rise directly to suspicions that such problems may arise. At least one indicators negative Eh values, occurrence Fe 2+ or occurrence sulphide must be fulfilled by results measurements groundwater composition at repository depth. If none indicators can clearly indicate absence dissolved oxygen, a more thorough chemical assessment is required. If not even se furr studies can indicate oxygen-free conditions, site must be aboned. Measured total salinities (TDS = Total Dissolved Solids) at repository level must be lower than 100 g/l. Occasional higher values can be accepted if it can be shown that water is located in areas that can be avoided that water will not be able to flow to repository area. Besides se direct disqualifying criteria, suitability site can be questioned if a large fraction rock mass between fracture zones has a hydraulic conductivity greater than 10 8 m/s. High permeability rock requires local precision adaptation repository if safety margins are to be met. 9

9 Contents 1 Introduction Purpose Goal Background Context related work Safety assessment SR Overall programme for investigation evaluation sites This report 22 2 General requirements preferences Laws, ordinances regulations Environmental Code Nuclear Activities Act Radiation Protection Act Regulations draft regulations What makes deep repository safe? Safety principles Safety assessment How safety assessment can be used to formulate requirements preferences regarding rock Fundamental civil engineering aspects Or general requirements preferences 30 3 Premises, terms methods Premises Definitions Influence on function deep repository Breakdown to functions within different disciplines Presentation tables Requirements preferences regarding parameters Geoscientific parameters Determination geoscientific suitability indicators Criteria Siting stages criteria The work formulating criteria Comparison between sites? 43 4 Geology Geological conditions that influence function deep repository Influence on canister integrity Influence on isolating capacity buffer Influence on isolating retarding capacity rock Biosphere-related matters Construction-related matters 46 11

10 4.2 Topography Description parameter its influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Soils Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Rock types Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Structural geology plastic shear zones Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Structural geology Fracture zones fractures Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Summary suitability indicators geology 57 5 Rock mechanics Influence on function deep repository Overview Influence on canister integrity Influence on isolating retarding capacity buffer Influence on retarding capacity rock Construction-related matters Initial rock stresses Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Mechanical properties intact rock Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Fractures fracture zones Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Mechanical properties rock mass as a whole Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria 69 12

11 5.6 Coefficient rmal expansion Description parameter its influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Future loads Description parameters ir influence on functions Requirements preferences Usefulness as suitability indicators Summary suitability indicators rock mechanics 71 6 Temperature Thermal properties that influence function deep repository Influence on canister integrity Influence on isolating retarding capacity buffer Influence on isolating retarding capacity rock Biosphere-related matters Construction-related matters Parameters that describe heat transport Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Ambient temperatures Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Summary suitability indicators temperature 78 7 Hydrogeology Influence on function deep repository Influence on canister integrity Influence on isolating capacity buffer Influence on retarding capacity geosphere Biosphere-related matters Construction-related matters Permeability Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Porosity storage coefficients Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Properties groundwater Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria 87 13

12 7.5 Near-surface ecosystems Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Boundary conditions supporting data Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Summary suitability indicators hydrogeology 91 8 Chemistry groundwater composition Influence on function deep repository Influence on canister integrity Influence on release to groundwater Influence on stability buffer Influence on retardation in geosphere Biosphere-related matters Construction-related matters Indications occurrence dissolved oxygen Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria ph Description parameter its influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Total Dissolved Solids (TDS) Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Organic substances or components in groundwater Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Summary suitability indicators chemistry Transport properties rock Influence on function deep repository Influence on integrity canister buffer Influence on retarding capacity geosphere Flow parameters on deposition hole scale Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria

13 9.3 Properties flow paths Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Properties rock matrix along flow paths Description parameters ir influence on functions Requirements preferences Generic knowledge knowledge obtained at different stages Suitability indicators criteria Summary suitability indicators transport properties rock Conclusions Results What requirements do we make on rock? Choice areas for site investigation Under what circumstances should site investigation be discontinued? Experience from project work References 119 Appendix A Function tables 127 Appendix B Parameter tables

14 1 Introduction This report gives account what requirements preferences are made by deep repository on rock what criteria should be used for evaluation sites in conjunction with site investigations. The work was initiated in An interim report was submitted in conjunction with RD&D-Programme 98 /SKB, 1998/. 1.1 Purpose When SKB s programme for final disposal spent nuclear fuel moves into site investigation phase, it is necessary to define exactly which measurable properties in rock may be importance for long-term safety which may be importance for being able to build repository on investigated site in a rational manner. The information is needed to provide guidance on selection sites, to provide guidance on what is to be measured in site investigation, to be able to evaluate site during ongoing investigation in a structured manner. Laws ordinances require that deep repository be safe. To check that requirement is met, SKB carries out a safety assessment. The assessment deals with a large number processes in repository in rock that influence repository s performance evolution with time. The repository site could also be affected by many different events circumstances. This makes it difficult to specify detailed requirements on different properties rock on initial conditions on repository site. The requirements, preferences criteria that can be made on rock can refore only provide guidance. They do not take place overall complete safety assessments. The question siting deep repository is currently being considered in many countries. The progress report /Ström et al., 1998/ provides a brief description situation in a number countries with a special emphasis on to what extent requirements criteria have been formulated for rock. General international recommendations exist, such as IAEA s document Siting deep geological repositories /IAEA, 1994/. The present report provides guidance in siting a deep repository for spent nuclear fuel KBS-3 type in Swedish crystalline bedrock. The work cannot be used directly as a basis for siting or types repositories or in or geological settings. 17

15 1.2 Goal The goal project has been to answer, as clearly as possible, following questions: What requirements are made on rock for it to be suitable for a deep repository for spent nuclear fuel KBS-3 type, what conditions in rock render it unsuitable for a repository? What conditions in rock are advantageous for such a deep repository? The answers to se questions have a great influence on continued siting work. They clarify geoscientific goals feasibility studies site investigations y influence how site investigation programme should be structured. The more detailed goals project have been to: identify quantify requirements preferences regarding rock s properties conditions from perspectives long-term safety engineering feasibility, propose criteria that can be used both to assess fulfilment requirements preferences, if possible, to compare sites after feasibility studies during site investigations. 1.3 Background The schematic design a deep repository for spent nuclear fuel proposed by SKB, KBS-3, has been analyzed developed over a period more than 20 years. The feasibility disposing nuclear waste in Swedish crystalline bedrock have been analyzed over an even longer period time. The suitability method has been demonstrated in a number safety assessments such as KBS-3 /KBS, 1983/ most recently in SR 97 /SKB, 1999a/. Long experience exists in Sweden rock cavern construction in crystalline bedrock from mines engineering projects. Great efforts have been devoted over a long time to geoscientific characterization properties structural composition bedrock. The interim goal being able to choose at least two sites for site investigations in 2001 is set in SKB s RD&D-Programme 98 /SKB, 1998/. The work developing geoscientific suitability indicators comprises a part extensive background material SKB needs to commence successfully carry out site investigations. The need for suitability indicators has also been expressed for several years by regulatory authorities Swedish Government in ir reviews findings on SKB s RD&D programmes. General siting factors have been described previously by SKB, for example in conjunction with supplement to RD&D-Programme 92 /SKB, 1994/. These factors were n accepted by Government regulatory authorities...as a suitable point departure for continued work. At same time, SKB considered it necessary in preparation for site investigations to define factors criteria more precisely. In General Siting Study 95 /SKB, 1995b/, SKB described conditions on a national scale as a general background to fundamental prospects for siting a deep repository. An extensive project was carried out in 1996 to identify all parameters that can be determined in a geoscientific site investigation. The results were published in a separate report /Andersson et al., 1998a/. 18

16 The Government s decision 19 December 1996 in response to SKB s RD&D- Programme 95 /SKB, 1995a/ states that General Siting Study 95 /SKB, 1995b/ should be supplemented. A progress report /Ström et al., 1998/ on project was published in conjunction with presentation RD&D-Programme 98 /SKB, 1998/ which, toger with a separate analysis questions relating to a coastal/inl siting comparisons between norrn sourn Sweden /Leijon, 1998/, constituted supplement called for by Government. The Government s decision 24 January 2000 in response to SKB s RD&D- Programme 98 /SKB, 1998/ stipulates a number conditions for continued research development programme. According to se conditions, SKB shall Present an overall evaluation completed feasibility studies or material for selection sites for site investigations. SKI s statement comment on RD&D-Programme 98 /SKI, 1999/ states following: SKI is however in full agreement with SKB that suitability a site for a repository must ultimately be judged on basis an integrated safety design analysis that takes into account uncertainties interaction between different factors. The criteria fulfil an important function in clarifying what characterises a suitable site for a repository. However, on ir own, criteria do not provide an adequate basis for judging wher site complies with basic safety criteria. SKI also stresses coupling between work developing siting factors work with safety assessment SR 97: On basis an up-to-date safety assessment (SR 97), SKB must also reconcile clearly account for minimum criteria discriminating factors which determine wher a site can be judged to be suitable for a repository. SR 97, in addition to demonstrating safety assessment methodology, should also provide a basis for...specifying factors on which selection sites for site investigation will be based; deriving parameters which must be determined or criteria which should be made with respect to a site investigation.... These requests from SKI are satisfied by fact that work in this project is to a high degree based on results insights achieved in SR 97. This is also evident from different references on which report is based. 1.4 Context related work In response to Government s decision on RD&D-Programme 98, statements from Swedish Nuclear Power Inspectorate viewpoints from feasibility study municipalities, SKB intends to submit a supplementary account in accordance with conditions in Government s decision. The account is planned to be contained in a report, RD&D-98 supplement, with sections Method selection, Selection investigation sites, Programme for site investigations Consultation. The present report comprises a portion supporting material for RD&D-98 supplement. Examples or supporting material are SR 97, site investigation evaluation programme compilation feasibility studies, or siting material with choice sites. Figure 1-1 provides an overview scope supporting material. 19

17 Figure 1-1. Overview SKB s overall account in preparation for site investigation phase, i.e. supplement to RD&D-98. The work with requirements criteria comprises one main references Safety assessment SR 97 A central point departure for project work has been SR 97 safety assessment published by SKB in December Several goals SR 97 have a direct bearing on work with requirements, preferences criteria. These goals are: SR 97 shall provide supporting material for demonstrating feasibility finding a site in Swedish bedrock where KBS-3 method for deep disposal spent nuclear fuel meets requirements on long-term safety radiation protection that are defined in SSI s SKI s regulations. SR 97 shall provide supporting material for specifying factors that serve as a basis for selection areas for site investigation deriving what parameters need to be determined what or requirements should be made on a site investigation. SR 97 shall provide supporting material for deriving preliminary functional requirements on canister or barriers. 20

18 The fundamental structure a safety assessment how it can be used to define suitability indicators is discussed in section 2.2. This report is based to a high degree on results analyses carried out within SR 97. SR 97 consists a separate Main Report /SKB, 1999a/ three sub-reports ( Repository System Report ) /SKB, 1999c/, Process Report /SKB, 1999b/ Data Report /Andersson, 1999/. Both main report sub-reports are based in turn on results reported in a large number or reports Overall programme for investigation evaluation sites The preparatory work for site investigations also includes developing a distinct site investigation programme. By site investigation programme is meant here an overall programme for investigation evaluation sites with respect to long-term safety technology. The programme should thus detail what information is intended to be collected from a site how it is to be used in evaluation a site. This is where present report enters into picture. The evaluation programme will demonstrate use requirements, preferences, indicators criteria during ongoing site investigations. Figure 1-2 provides overview se related activities how y are linked to each or. The overall programme will be supplemented detailed in discipline-specific programmes. These are also generic, i.e. not tailored to specific conditions that exist on a particular site. When areas for site investigations have been selected, discipline-specific programmes will be reworked into site-specific execution programmes. These will take into account site-specific geological conditions, as well as l environmental interests societal circumstances. Figure 1-2. Outline site investigations an overview related activities how y are linked to each or. 21

19 1.5 This report Chapters 1 3 describe premises employed methodology. The actual account work is found in Chapters 4 9. The conclusions work are presented in Chapter 10. Chapter 2 describes what fundamental requirements a deep repository must satisfy. Requirements preferences that are presented in this chapter comprise basis work formulating more detailed requirements preferences regarding rock. Chapter 3 gives an account premises for work. This includes definitions terms function, parameter, requirement, preference, suitability indicator criterion. During project work it has proved necessary to use a strict vocabulary structure in reports. The procedure for developing criteria proceeds in steps, it should be possible to underst how a concrete requirement or preference regarding a given property rock is derived from one more fundamental requirements which deep repository must satisfy. Chapters 4 to 9 present requirements preferences regarding function deep repository, requirements preferences regarding properties rock (parameters), expected value ranges for se parameters, proposals (with reasons given) for criteria to be used during after a feasibility study, as well as during after site investigations. Chapter 4 deals with geology, Chapter 5 rock mechanics, Chapter 6 temperature properties, Chapter 7 hydrogeology, Chapter 8 groundwater composition (chemistry), Chapter 9 transport properties rock. The contents se chapters are also summarized in tables in Appendices A B. 22

20 2 General requirements preferences There are fundamental requirements which a deep repository must satisfy. These requirements are defined by laws regulations issued by regulatory authorities. The safety deep repository is based on safety functions isolation retardation. These functions are affected both by design construction facility engineered barriers, by site-specific conditions on repository site. A safety assessment is carried out in order to evaluate safety. A number general requirements preferences can also be formulated for actual construction work. They serve as a basis for work formulating detailed requirements preferences regarding rock. 2.1 Laws, ordinances regulations The general requirements on deep repository emanate from acts law passed by Swedish Parliament. The most important laws in this regard are Environmental Code, Nuclear Activities Act Radiation Protection Act. Permits under both Environmental Code Nuclear Activities Act are required to build a deep repository Environmental Code The Environmental Code regulates, among or things, issuance permits for siting deep repository preparation environmental impact statements. The code furr regulates what environmental impact deep repository can be permitted to have Nuclear Activities Act Radiation Protection Act Requirements on safety radiation protection are set forth in Nuclear Activities Act Radiation Protection Act. The Nuclear Activities Act prescribes in general that nuclear activities shall be conducted in a safe manner. The Radiation Protection Act prescribes in general that anyone conducting activities with radiation shall, depending on nature activities conditions under which y are conducted, adopt whatever measures precautions are needed to prevent or counteract harm to humans, animals environment. The ordinances issued by Government pursuant to Nuclear Activities Act Radiation Protection Act contain some more detailed provisions regulate activities Swedish Nuclear Power Inspectorate (SKI) Swedish Radiation Protection Institute (SSI). The ordinances are still couched in very general terms regarding requirements on safety radiation protection in deep repository. 23

21 2.1.3 Regulations draft regulations In addition to laws mentioned above, SKI SSI are empowered to issue regulations. The National Radiation Protection Institute (SSI) recently issued regulations concerning final disposal spent nuclear fuel /SSI, 1998/. Some provisions se regulations have a bearing on work with siting factors criteria. The final disposal spent nuclear fuel shall be radiologically optimized based on best available technology. A final repository for spent nuclear fuel or nuclear waste shall be designed so that annual risk after closure is no more than 10 6 for individual exposed to greatest risk. Furrmore, final disposal shall be carried out in such a manner that biological diversity is preserved a sustainable utilization biological resources is protected against harmful effects radiation. The Swedish Nuclear Power Inspectorate (SKI) has sent out draft regulations governing safety in final disposal spent nuclear fuel etc. It is stated re that safety, in both short long term, shall be based on a system passive natural barriers that a deficiency that might arise in one barriers should not impair safety final repository. It is furr stated in proposal that features, events processes that are importance for post-closure safety a final repository should be analyzed before repository is built, before it is commissioned before it is closed. The question wher fundamental requirements are met for a deep repository on a specific site will be considered in conjunction with regulatory review safety assessments environmental impact statements which SKB is obligated to submit. It should also be observed that regulations do not directly stipulate requirements on performance different parts deep disposal system, but discuss in more general terms requirements on system as a whole. In or words, laws regulations cannot be used directly to formulate requirements or preferences on properties rock. Such requirements or preferences can only be derived indirectly, based on impact y may have on safety repository. When it comes to actual construction deep repository, National Board Occupational Safety Health stipulates specific requirements on rock works (AFS 1997:3) on blasting works (AFS 1994:17). These provisions must be taken into account in planning construction deep repository reby also impact site investigations. 2.2 What makes deep repository safe? Safety principles The safety principles for a deep repository are presented in SR 97. A deep repository shall primarily isolate waste. If isolation function should for any reason fail in any respect, a secondary purpose repository is to retard release radionuclides. This safety is achieved by a system barriers, see Figure 2-1: The fuel is placed in corrosion-resistant copper canisters. Inside five-metre-long canisters is a cast iron insert that provides necessary mechanical strength. The canisters are surrounded by a layer bentonite clay that protects canister mechanically in event rock movements prevents groundwater from flowing around canister, which prevents corrosive substances from entering canister. The bentonite clay also effectively adsorbs radionuclides that are released if canisters should be damaged. 24

22 Figure 2-1. The KBS-3 system with main alternative that canisters are deposited one by one in vertical holes. Variants with several canisters per hole or with horizontal holes may also be considered. The conclusions report are also applicable to se variants. The canisters with surrounding bentonite clay are emplaced at a depth about 500 metres in crystalline bedrock, where mechanical chemical conditions are stable. If any canister should be damaged, chemical properties fuel radioactive substances, for example ir poor solubility in water, put severe limitations on transport radionuclides from repository to ground surface. This is particularly true those elements with highest long-term radiotoxicity, such as americium plutonium. The repository is thus built up several barriers which support complement each or. The safety repository must be adequate even if one barrier should be defective or fail to perform as intended. This is essence multiple barrier principle. Anor principle is to make repository nature-like, i.e. to use natural materials such as copper for outer shell canister bentonite clay for buffer. Choosing materials from nature makes it possible to judge evaluate materials long-term stability behaviour in a deep repository based on knowledge natural deposits. For same reason, repository should cause as little disturbance natural conditions in rock as possible. Above all, an attempt is made to limit chemical impact repository in rock. 25

23 The main alternative for KBS-3 method is that canisters are deposited one by one in vertical holes from deposition tunnels (Figure 2.1). The variants that may be considered are: vertical deposition two canisters in each hole, horizontal deposition several canisters per hole. The results conclusions this report are also applicable to se variants. Isolation primary function repository The primary function deep repository is to isolate waste from man environment. This is achieved directly by copper canister. The buffer is supposed to contribute to isolation function by keeping canister in place preventing corrosive substances from coming into contact with canister. The rock also contributes to this isolation by fering a stable chemical mechanical environment for canisters buffer. Chemical conditions are determined primarily by composition groundwater. It is advantageous if water contains low concentrations substances that could be harmful to copper canister bentonite. It is also advantageous if water flows slowly past repository so that influx undesirable substances is limited. Mechanically, Swedish crystalline bedrock fers a long-term stable environment for a deep repository. Retardation secondary function repository If isolating function should for some reason be compromised, or if any canister should have an initial defect not detected by post-fabrication inspection, repository has a secondary retarding function. By this is meant that time it takes for radionuclides to be transported from repository to biosphere is long enough so that ir radiotoxicity declines considerably before radionuclides reach man or human environment. All barriers contribute to retarding function repository. Even a partially damaged copper canister can effectively contribute to retardation by impeding influx water into canister transport released radionuclides out it. The fuel, in which majority radionuclides lie embedded, consists a durable ceramic material which makes a significant contribution to retardation. If fuel comes into contact with groundwater, a very slow dissolution process starts which leads to release radionuclides. This release is limited by fact that many radionuclides with highest long-term toxicity are poorly soluble in water, medium in which radionuclides might conceivably be transported through both pores buffer fracture system in rock. The clay buffer should have a capacity to retain many radionuclides with highest long-term toxicity by adherence to surfaces clay particles. The rock is supposed to contribute to this retardation by virtue fact that radionuclides adhere to surfaces fractures /or penetrate into micrractures containing stationary water so that y have a much longer travel time than groundwater itself. Besides actual design deep repository, it is primarily composition (chemistry) groundwater, groundwater flow in rock (hydrogeology) transport properties rock that influence repository s retarding function. 26

24 Dilution dispersal Dilution dispersal have also previously also been mentioned as a third safety function: By locating repository so that any releases are highly diluted in biosphere, consequences are mitigated. This effect is not regarded as a safety function in safety assessment SR 97 /SKB, 1999/ for several reasons: The biosphere, where dilution takes place, changes much faster than repository system, in a way that is difficult to predict. It is refore not reasonable to base a long-term safety function on conditions in biosphere. Although consequences for those most affected by a release are mitigated, a larger population may be affected. Dilution is neverless an important factor that influences radionuclide migration in biosphere reby consequences a release from repository. An evaluation dilution conditions at a repository site must refore be included in a safety assessment, but dilution is not regarded as a safety function in itself Safety assessment A safety assessment is carried out in order to evaluate long-term safety. The purpose, contents outline a safety assessment are described in detail in SR 97. In brief, safety assessment can be said to consist : a thorough description appearance or state repository system when it has just been built, a survey what changes repository can be expected to undergo with time as a consequence both internal processes external forces, an evaluation consequences changes for long-term safety. This approach is common in analysis systems that change with time. A system is delimited by a system boundary an initial state is described. The evolution system is reafter determined by time-dependent, internal processes interaction with changing surroundings. Just as important as assessment repository s isolating capacity numerical result analysis retardation is confidence in results. The data underlying a safety assessment are always associated with deficiencies various kinds. To put it simply, we are faced with task showing that repository has been designed with sufficient margins to be safe in spite incomplete knowledge available. Confidence in results is dependent on how methodically uncertainties/ deficiencies have been hled. The execution presentation SR 97 can be divided into a number steps: System description: First a structured description is performed all internal processes, ir interrelationships properties repository that are influenced by a particular process. This task also includes defining boundary between a system its surroundings. Initial state: The initial state repository, i.e. what it looks like when it has just been completed, is n described (dimensions materials in engineered portions repository structure properties geosphere around repository). 27

25 Choice scenarios: The evolution repository is influenced by its surroundings. To cover different situations in surroundings, evolution repository is analyzed for a number different sequences events in surroundings: a number different scenarios are selected analyzed. The chosen scenarios should toger provide reasonable coverage different evolutionary pathways repository its surroundings could conceivably take. Analysis chosen scenarios: With aid system description, evolution repository is analyzed for each chosen scenarios. A number different tools methods are used here, ranging from discussions simple approximations to detailed modelling based on site-specific data. For scenarios where a canister is damaged, calculations are made radionuclide transport from damaged canister through different barriers, what dose this release could give rise to. The calculations are performed with a chain transport models (COMP23, FARF31, BIO42), which in turn obtain input data from various more or less complex model calculations or data analyses different conditions or phenomena, see Figure 2-2. Figure 2-2. Models used in SR 97 for calculation radionuclide transport (rectangles) input data for se models (ellipses). 28

26 Evaluation: Finally, an overall assessment is made repository safety, where different scenarios are weighed toger into a total risk picture. The conclusions overall assessment comprise results safety assessment. Confidence in results in light uncertainties that exist in data underlying assessment must also be discussed here How safety assessment can be used to formulate requirements preferences regarding rock The work developing geoscientific suitability indicators criteria is based on many years experience, analyses development KBS-3 method. The safety assessment SR 97 has comprised an essential complement to data used in project. The assessments what is essential from viewpoint long-term safety are based on analyses performed within framework SR 97, complemented with previous knowledge experience. For each site-related parameter needed to describe safety assessment s initial state (see above), question has been asked wher this parameter should be a geoscientific suitability indicator. The safety assessment has been used to seek an answer to question wher that are value ranges where deep repository s isolation can be threatened. As a precaution, such value ranges have comprised a basis for formulating requirements, even though it is not always clear that deep repository would definitely be unsafe if requirements were not met. The requirements can only be reconsidered in light new knowledge or if design repository is significantly altered. The safety assessment has also been used to find grounds for preferences regarding value ranges that contribute to good isolation or good retardation. Such value ranges result in desired function, but do not necessarily define borderline to unacceptable function. Such a borderline is in many cases influenced by or parameters, is relative, is unknown or can be influenced by repository layout. The requirements define conditions that may not occur. The preferences define conditions that lead to good isolation retardation, but deep repository may very well turn out to be safe even if many preferences are not satisfied. The requirements preferences have been formulated to provide guidance in siting work to be able to prioritize investigation activities in site investigations. They do not take place integrated complete safety assessments. (Chapter 3 provides stricter definitions terms function, parameter, requirement, preference, suitability indicator criterion.) 2.3 Fundamental civil engineering aspects Requirements preferences that are framed from rock engineering perspective are a somewhat different character than direct safety requirements. The repository layout is designed primarily to achieve as good performance safety as possible: canister tunnel spacings are determined by requirements on temperature in around repository, major discontinuities are avoided, etc. Furrmore, pure rock excavation aspects such as water seepage rock stability in tunnels will be taken into account. The general rule is that conditions that are favourable from a safety viewpoint also entail good constructability a safe working environment. Good constructability 29

27 a stable rock facility are furr advantageous for safety during operation facility. There is refore seldom any conflict between requirements preferences that can be formulated from different viewpoints. The general requirements from a civil engineering perspective can be summarized in following points: working environment shall be safe, environmental impact investigations, construction operation shall be limited kept within acceptable levels, construction shall only have a limited transient impact on safety functions deep repository, excavation deposition areas shall be able to take place at same time as deposition in or areas. Beyond this re are preferences that rock work can be done with as few interruptions as little use extraordinary reinforcement sealing measures as possible (good constructability), deposition area does not have to be split up into a very large number subareas, that it is possible to position deposition tunnels in a flexible manner in selected deposition areas. During after site investigations, a construction analysis is carried out for chosen repository layout where constructability, time material consumption, environmental impact, working environment, etc. for rock construction are analyzed. If safety assessment or construction analysis indicates unreasonable consequences or costs for chosen layout, latter needs to be changed. In or words, construction analysis does not impose any absolute requirements, since adjustments can generally be made to suit prevailing conditions. There are, on or h, a number factors that influence constructability costs. 2.4 Or general requirements preferences As noted earlier, work reported here is restricted to properties rock soil. This means that such aspects as transportation, l use, management natural resources societal factors are not dealt with in present report. Prior to selection sites for site investigations selection a site for detailed characterization, all conditions that can influence choice need to be considered, not just geoscientific conditions. All geoscientific requirements must course be satisfied. Prior to selection a site for detailed characterization, a safety assessment must show that a safe deep repository can be built re. However, many geoscientific preferences are such that, if y are satisfied, this entails lower costs or a shorter investigation time. In site selection, such preferences must be weighed against or environmental societal preferences. SKB will explain how this weighingtoger should be done in anor context. Ongoing upcoming EIA consultations deal with se matters will clarify se or aspects. 30

28 3 Premises, terms methods The project work has departed from a number premises has proceeded stepwise. Certain fundamental terms are defined in this chapter, after which methodology used in work is described. 3.1 Premises The following premises apply to work: The project is limited to formulation requirements, preferences, suitability indicators criteria. Requirements preferences pertain to a repository for spent nuclear fuel KBS-3 type, i.e. a repository where fuel is contained in copper canisters embedded in bentonite clay at a depth m in Swedish crystalline basement (see section 2.2). (It should however be noted that conditions that are suitable or less suitable for a KBS-3 repository with variants can also be assumed to be suitable or less suitable, respectively, for or designs a deep repository in crystalline bedrock. More specific requirements preferences, as well as relative importance different factors, can, however, change if or repository designs are studied.) The work has been limited to discussing properties rock soil. This delimitation entails that matters pertaining to e.g. transportation, l use management natural resources, or societal factors, are not dealt with or than cursorily. (These matters are dealt with in or parts SKB s siting studies.) Precise definition criteria is limited to stages prior to site investigation during after completed site investigation. In certain cases, however, a oretical discussion criteria is held that only becomes meaningful during detailed characterization or deposition phases. 3.2 Definitions A vital point departure for this project is to differentiate between requirements preferences that can be made on rock, what different measurements can be performed to try to determine properties rock, what decisions can be made when measurement results have been analyzed. Concepts such as siting factor criteria are ten used without defining term. It also seems as if words have been used in slightly different senses in different contexts. Stricter definitions a number terms are refore used in this study (see also Table 3-1): By function a deep repository is meant purposes which deep repository is intended to serve, for example to have an isolating retarding function. Example function: canister should isolate waste from surroundings, rock should retard any escaping radionuclides. By performance is meant how well this function is served. 31

29 By parameter is meant a physical or chemical quantity (property, condition, state, variable, feature) relevance to deep repository. A parameter can assume different values. Example: orientation water-bearing structures, flow porosity, ph. By requirement is meant a condition that must be satisfied. Requirements may relate to eir functions or individual parameters. Requirements define limits what is not acceptable on a site. Example: requirement that groundwater at repository level may not contain dissolved oxygen can be established based on fundamental safety function that integrity canister (isolation) may not be threatened. Preferences refer to conditions that ought to be satisfied. Preferences may relate to eir functions or individual parameters. Preferences define what is good, but not necessary. Example: preference that rock should have high rmal conductivity can be established based on construction design preference fitting as many canisters as possible within a given deposition area. By geoscientific suitability indicators is meant parameters that describe properties states rock groundwater for which re exist site-specific values or assessment grounds which can be used at one or more stages siting work to determine to what extent requirements preferences are satisfied. Example: occurrence Fe 2+, indicating oxygen-free conditions. By criteria for site evaluation is meant indicative values suitability indicators which can, in a given stage, be used to determine wher a site satisfies stipulated requirements preferences. Criteria are linked to level knowledge refore change from one siting stage to anor. Example: measured occurrence Fe 2+ for quality-approved water samples during site investigation could be used as a criterion for verifying requirement that groundwater must not contain dissolved oxygen at repository depth. Requirements preferences pertain to actual conditions y remain same during different stages siting work. What can change requirements preferences are changed premises, a new repository concept or significant new knowledge. All requirements must be satisfied. Satisfying preferences generally leads to greater safety margins, lower costs, simpler investigations or a simpler design repository. All preferences do not have to be satisfied in order for a site to be approved for a deep repository. It is very possible that poorer values for certain parameters are compensated for by better values for ors. An integrated safety assessment construction analysis are refore always needed to assess safety performance. Preferences, as y are formulated in this report, merely provide guidance, but cannot take place safety assessment. The term geoscientific suitability indicator is used in this study instead term siting factor, which has ten been used previously in discussions siting deep repository. The reason for this is partly that term siting factor has been used in several senses, but above all that term suitability indicator corresponds more closely to what is usually used in or environmental contexts. The stard ISO , which has to do with environmental management environmental performance evaluation, defines environmental condition indicator as a specific expression that provides information about local, national or global condition environment, i.e. a descriptive term. Addition words geoscientific suitability clarifies fact that indicators are intended to describe which features rock are importance for judging wher rock is suitable from viewpoint long-term safety engineering. The word indicator also clarifies fact that project is not about weighting factors. 32

30 The distinction between requirements/preferences criteria is necessary, since geoscientific investigations never provide complete knowledge state properties rock groundwater. When assessing site-specific data, it is refore necessary to evaluate precision parameter estimate against stipulated requirements preferences. A suitability indicator, reby a criterion as well, is based on something that can be measured or estimated. Figure 3-1 illustrates hierarchy for requirements, preferences criteria which has been point departure for work formulating suitability indicators criteria for m. Fundamental safety civil engineering functions The rock shall contribute to isolating retarding functions deep repository fer good conditions for repository layout construction Requirements preferences regarding influence rock on deep repository performance Example: Requirement that buffer s swelling pressure be preserved Maximum temperature on canister surface (isolation) Requirements preferences regarding geoscientific parameters Example: Requirement that total salinity (TDS) be lower than 100 g/l in deposition area. (Temperature requirements are complied with by layout. No requirements on rock.) Figure 3-1. Illustration requirement hierarchy that has been point departure for work. Requirements on ( site ) rock that must be satisfied for deep repository to be considered safe for disposal (pertains to actual conditions, regardless siting, construction or operating stage). Not all requirements on function lead to requirements on rock. Table 3-1. Brief definitions central terms. Term Function Parameter Requirement Preference Geoscientific suitability indicators Criteria for evaluation Definition Purpose which deep repository is intended to serve, for example to have an isolating retarding function. Physical or chemical quantity (property, condition in rock). Condition that must be satisfied, refers to actual conditions regardless siting stage. All requirements must be satisfied. Condition that ought to be satisfied regardless siting stage. All preferences do not have to be satisfied, however. Measurable or estimable site-specific parameters that can be used in a given siting stage to assess wher requirements preferences are satisfied. Values for suitability indicators in a given siting stage that are decisive for site assessment wher a site satisfies stipulated requirements preferences. 33

31 3.3 Influence on function deep repository The requirements preferences that can be made on deep repository mainly have to do with which functions must or ought to be satisfied. An analysis function includes a number geoscientific parameters, which are schematically illustrated in Figure 3-2, in some cases requirements on a given function can, after analysis, be broken down into requirements on individual parameters. In many cases, however, it is difficult to carry out this breakdown, since function is dependent upon interacting conditions for many parameters. A certain function can be achieved by many different combinations parameter values. Figure 3-2. Illustration how geoscientific models are utilized for design for safety performance assessment. Data on properties rock (parameters) serve as a basis for geoscientific models bedrock reby for assessment repository performance. 34

32 3.3.1 Breakdown to functions within different disciplines The general requirements preferences regarding performance deep repository that were described in Chapter 2 have been broken down particularized. The question is asked, each in turn, wher geological conditions, rock-mechanical properties, rmal properties, hydrogeological properties, groundwater composition or transport properties rock influence various functions deep repository. If influence is significant, requirements or preferences are formulated on how great this influence may be. Furrmore, function analyses are identified that can be used during ongoing site evaluation to check requirements preferences. The concerned geoscientific parameters are also specified Presentation tables Requirements preferences from a functional perspective have been arranged by geoscientific discipline. The structuring has been carried out with aid tables divided into disciplines geology, rmal properties, hydrogeology, rock mechanics, chemistry transport properties. A table whose rows correspond to general requirements on safety functions has been set up for each discipline. Table 3-2 shows an excerpt from such a table. The tables are shown in ir entirety in Appendix A. The contents tables are also presented as first section in each Chapters 4 9. Each table is divided into following columns: concerned function, specific conditions that influence function, requirements, preferences, function analysis concerned parameters, references. The purpose se columns is discussed in following. Table 3-2. Example structure that has been devised for presentation requirements preferences regarding influence rock on function deep repository. The example is taken from discipline temperature fundamental safety function pertaining to isolating function canister. The complete function table is shown in Appendix A. Concerned Thermal Requirements Preferences Function analysis References function conditions concerned parameters that influence function Influence on Temperature Requirement Layout is determined so that Werme, integrity on canister on maximum temperature requirement SR 97 canister surface temperature is met. The temperature Base scenario buffer influences on canister near-field is determined chemical surface by layout, rmal conductivity, environment T< 100 C. heat capacity, boundary condi reby tions, bentonite saturation. canister function. 35

33 Concerned function The general requirements preferences regarding function deep repository that have served as a point departure for formulation more detailed requirements preferences (see Chapter 2). Specific conditions that influence function The discipline-specific conditions importance, i.e. ones that can influence function, are given for each general safety function. Requirements Discipline-specific requirements are given where possible. In principle, only prohibitive requirements are noted here, i.e. if requirement is not satisfied, this means that site for deep repository is unsuitable or that repository layout has to be decisively modified. Moreover, safety function is not automatically satisfied even if all requirements are met. The requirements should indicate limits for what is not acceptable. Preferences Discipline-specific preferences are given where possible. The preferences should provide guidance on what is needed in order for a safety assessment or a construction analysis to indicate satisfactory conditions. The preferences may reby relate to e.g. known value ranges for satisfactory conditions, but do not have to define exact limit for unacceptable function, since such a limit is in many cases relative, unknown or can be influenced by modification repository layout. In preparation for a decision to commence detailed characterization apply for a permit for construction a deep repository, an integrated safety assessment must in any case be carried out. If all essential preferences are satisfied, this assessment should in all probability indicate that deep repository possesses satisfactory safety that good conditions exist for successful execution civil engineering works. Function analyses concerned parameters In column headed function analyses, analyses (calculations etc.) that can be used to analyze function are specified, along with which parameters are primarily taken into account in such an analysis. After completed function analyses, requirements preferences can be more precisely defined. 3.4 Requirements preferences regarding parameters On basis identified requirements preferences regarding function deep repository, extent to which it is possible to formulate requirements or preferences directly on parameters that determine function is analyzed. 36

34 3.4.1 Geoscientific parameters SKB has identified parameters importance to determine during geoscientific site investigation /Andersson et al., 1996/. The parameters are classified according to geoscientific disciplines: geology, rock mechanics, rmal properties, hydrogeology, hydrogeochemistry transport properties. This report has also been translated to English /Andersson et al., 1998a/, with some marginal changes a few supplementary figures. The parameters presented in report include all siting factors presented in /SKB, 1994/. /Andersson et al., a/: identifies, describes evaluates geoscientific parameters that are importance to know in order to be able to carry out performance safety assessments a deep repository, that can be obtained from a site investigation, discusses how identified parameters are used which site-specific measurements can be employed to determine parameter in question, presents discusses data needs for rock engineering, presents discusses data needs for description or environmental aspects, presents or data needs for analysis a general understing geoscientific conditions. It is also observed that few geoscientific parameters are measured directly, but are rar ten determined by means an interpretation procedure which can give rise to various errors uncertainties. Measurement error comprises only a small portion this uncertainty. Problems related to scale-dependent parameters spatial variation can give rise to more significant uncertainties. The relevance various geoscientific parameters refore needs to be considered in relation to methods measurement evaluation that are available for determining parameter. Most tests that are performed in field (e.g. injection tests, hydraulic fracturing, tracer tests etc.) provide indirect information on e.g. hydraulic conductivity, rock stresses or retention properties Determination geoscientific suitability indicators The suitability indicators comprise a subset all geoscientific parameters presented by /Andersson et al., 1998a/. The geoscientific suitability indicators are parameters that significantly influence functions deep repository. A systematic method has been used, just as in process for determining detailed requirements on how rock may influence functions deep repository. Structure for work tables The parameters have been arranged by geoscientific discipline. Each discipline gives rise to a table whose rows correspond to geoscientific parameters according to /Andersson et al., 1996/. The structure tables is shown by Table 3-3. The tables are presented in ir entirety in Appendix B. The contents tables also comprise main content Chapters 4 9 in this report. 37

35 Table 3-3. Example in tabular form structure used to identify explain geoscientific suitability indicators. The example is taken from discipline chemistry (hydrogeochemical composition) parameter TDS (Total Dissolved Solids). Clear requirements could be formulated for this parameter. The complete chemistry table is shown in Appendix B. Geoscientific Requirements Preferences Value range Possible Criteria during feasibility parameter regarding regarding in Swedish suitability study (FS) site parameter parameter crystalline indicator? investigation (SI) bedrock TDS (total TDS<100 g/l Around 1,000 m Yes FS: no (but attention in dissolved at repository depth 0 35 g/l. coastal areas) solids) level Up to 100 g/l has been SI: Quality-approved measmeasured at ured TDS concentrations 1,700 m depth. at repository level must meet requirements. Occasional higher values can be accepted if it can be shown that water is located in areas that can be avoided. Each table is divided into following columns (see Table 3-3): reference to function in function table, requirements regarding parameter, preferences regarding parameter, value range in Swedish bedrock, usefulness as suitability indicator, criteria. The column that refers to description functions analyses in function table has been omitted for reasons space. Information on how geoscientific parameter in question enters into different function analyses is given in this column. The column is, however, included in complete tables presented in Appendix B. Requirements regarding value ranges for parameter Wherever possible, requirements (regarding value ranges) are sought that can be directly related to individual parameters. In some cases it is possible to directly stipulate an impermissible value range for parameter on basis requirements made on function. As a rule, it is difficult to relate requirements directly to geoscientific parameters. There are several reasons for this: parameter is only one several parameters that determine a function, suitable value range depends on value or parameters, parameter may influence several functions, it is not certain that value ranges that are suitable for one function are also suitable for or functions, parameter influences a function that is only a preference according to function table. 38

36 Preferences regarding value ranges for parameter Preferences regarding values ranges for parameter in question are given in this column. The reason for giving preferences instead requirements has been explained above. Preferences are supposed to provide guidance on what is needed in order for a performance or safety assessment to result in satisfactory conditions. The preferences may reby relate to value ranges for parameter that result in a desired function, but do not have to define exact limit for unacceptable function, since such a limit is in many cases relative, unknown or can be influenced by modification repository layout. In preparation for a decision to commence detailed characterization apply for a permit for construction a deep repository, an integrated safety assessment must in any case be carried out. If all essential preferences are satisfied, it is highly probable that this assessment will indicate that deep repository possesses satisfactory safety that construction analysis will indicate good constructability. Value range in Swedish crystalline bedrock In cases where general knowledge exists regarding parameter s value or value range in Swedish crystalline bedrock, this has been documented. Value ranges are discussed for all geoscientific parameters not just for selected suitability indicators. Usefulness as suitability indicator The main purpose table as a whole is to systematically ascertain wher geoscientific parameters at any stage during siting work can be a possible suitability indicator. In ongoing projects, a geoscientific parameter is a useful suitability indicator if one following conditions is fulfilled: a direct requirement or an essential preference has been formulated for parameter, or parameter is expected to have a great influence on result one or more important function analyses. The parameter must furrmore be able to be determined during feasibility studies or site investigations. A brief explanation, based on above rules, is included in table for each parameter, see Appendix B. Knowledge level in different siting or investigation stages Based on list possible siting factors, level knowledge that can or should be reached in a feasibility study, site investigation detailed characterization is discussed. It is not reasonable to designate a parameter as a suitability indicator if parameter cannot be measured or orwise estimated. To be able to indicate wher a parameter is a useful suitability indicator, but above all to be able to specify criteria during after a given investigation stage, knowledge is needed concerning what precision can be expected in parameter estimation. Knowledge parameter increases from feasibility study (FS) to site investigation (SI) detailed characterization (DC). However, importance different investigation stages varies greatly between different parameters. Naturally, ambition level for different investigation stages can also influence extent to which a parameter can be determined. 39

37 Table 3-4. Example how knowledge a geoscientific parameter changes as siting work progresses. Of parameters in table, it is only for topography that full knowledge is achieved already during a feasibility study. Geoscientific Knowledge during Knowledge during Knowledge during parameter feasibility study (FS) site investigation (SI) detailed characterization (DC) TDS (Total Generic Site-specific information from May contribute new knowledge Dissolved) deep boreholes, sufficient to on TDS in low-permeable Solids characterize repository area. rock, but also entails a risk disturbances. Topography Full knowledge on Full knowledge Full knowledge regional scale Location, size, Location regional Reasonable precision for regional High precision for regional direction zones on surface local major fracture zones. local major fracture zones in fracture zones can be judged repository area. Fair for local, fractures Stochastic information on local small ones. Stochastic informaminor fracture zones fractures (frequency, orientation, size) tion on fractures. Knowledge location fracture zones fractures at tunnels. Permeability Generic for Spatial distribution Direct knowledge near tunnels. for rock mass selected geology mean values It is not always possible to quantify expected precision in a simple manner. However, it is possible to discuss precision qualitatively; Table 4-3 illustrates this with an example. Such a qualitative discussion is valuable as a basis for deciding which criteria can be linked to a given parameter at a given investigation stage. Based on information this kind, it is n possible to judge when suitability indicator will be applicable. Criteria See next section regarding criteria. 3.5 Criteria Criteria are formulated for parameters that are judged to be useful as suitability indicators. The criteria shall be able to be used to judge wher a site satisfies or does not satisfy stipulated requirements, to what extent preferences are satisfied. Above all, criteria are aimed at ensuring that unsuitable sites are excluded, which is in keeping with general recommendations issued by IAEA /IAEA, 1994/. The final judgement as to wher a repository at a given site is safe is, however, made in an integrated safety assessment. An integrated construction analysis is carried out to judge scope consequences civil engineering works. The criteria provide guidance on outcome analysis. The criteria may change during course siting work, since information on sites changes, but requirements preferences remain same. 40

38 3.5.1 Siting stages criteria Criteria are formulated for stages prior to during site investigation. The criteria need to be linked to information that is available at current stage siting work to decision-making situation in which y will be used. Prior to a site investigation it is important to be able to rule out obviously unsuitable areas identify areas that should be prioritized for furr investigations, i.e. areas where re are good prospects that site investigations will show that rock has suitable properties. Criteria should not be made too strict at this stage, in view limited information that is available on properties rock at depth. The criteria will be used to select suitable areas for site investigations. An evaluation wher all requirements preferences are satisfied has character an overall forecast. During a site investigation, it must be possible to show with great certainty wher a site is suitable or unsuitable as a deep repository site. Furr, it may be meaningful to use criteria to compare sites. When site investigation is finished, suitability sites is determined in an integrated evaluation within framework an integrated safety assessment an integrated construction analysis. During site investigation, site-specific data shall, in relation to previously specified criteria, provide good guidance on what such an integrated assessment is expected to result in. The criteria are based on importance different suitability indicators an assessment precision available information. They are formulated to serve as a basis for SKB s different decisions prior to during site investigation to clarify underlying data. They do not take place overall assessments that need to be made by SKB, competent authorities or decision-makers The work formulating criteria The work formulating criteria has started with all identified suitability indicators is primarily aimed at verifying wher a site is suitable or unsuitable. Based on estimated information quantity decision situation before during site investigation, already identified suitability indicators are analyzed by asking following questions: Which precise quantified criteria can be meaningfully used for selection areas for site investigations? What are consequences criteria not being satisfied? Which precise quantified criteria can be meaningfully used during site investigations for selection a site for detailed characterization? What are consequences criteria not being satisfied? Can safety or technical suitability only be judged in terms a site-specific function analysis or construction analysis? If so, which analysis needs to be done what are consequences different outcomes such an analysis? Is it possible to say wher certain outcomes, within suitable range, parameter estimates or function analyses are better than ors? Do se outcomes entail a substantial improvement function, or is improvement subordinate interest? 41

39 Table 3-5. Two examples relationship between requirements, suitability indicators, knowledge level criteria. Requirements relate to actual conditions regardless siting stage. Criteria are an application suitability indicators in a given stage as a basis for decision. The complete criteria formulations are presented later in report. General Feasibility Site Detailed Operation siting studies studies investigation characterization Requirement: No dissolved oxygen in groundwater at repository level Knowledge Generic Generic Site-specific May contribute May ontribute information from new knowledge in new nowledge in deep boreholes, low-permeable low-permeable which is sufficient rock, but also rock, but also to characterize entails a risk entails a risk repository area. disturbances. disturbances. Suitability Eh, [Fe 2+ ] [HS ] indicators as indicators absence dissolved oxygen. Examples No criteria No criteria At least one possible indicators low Eh, criteria occurrence Fe 2+ or occurrence HS must be satisfied. Orwise site must be aboned. Requirement: Deposition holes may not be intersected by fracture zones Knowledge Location Location Reasonable preci- High precision for Knowledge locaregional zones regional zones sion for regional regional local tion all fracture at surface can at surface can local major major fracture zones zones at deposition be judged be judged fracture zones. in repository area. holes. Fair for local, small Stochastic ones. Stochastic information information on on local minor fractures. Knowledge fracture zones location fracture fractures (frequency, zones fractures orientation, size) at tunnels. Suitability Location, orienta- Location, orienta- Location, orienta- Location, orienta- Length, orientaindicators tion, length tion, length tion, length tion, length tion, length width regional width regional width fracture width fracture width fracture fracture zones. fracture zones zones fractures. zones fractures. zones fractures. local, major fracture zones. Examples Large homoge- Furr studies Revise layout based Unsuitable location Direct verification possible neous areas with suitable in areas on new knowledge. for deposition tunnels requirement criteria large distance with such large If repository can be avoided. impossible. Unbetween regional distances be- does not fit (is split suitable positions fracture zones are tween interpreted into a number for deposition holes interest for regional fracture parts),anor site can be avoided. furr studies. zones that y should be chosen. accommodate a repository. 42

40 An example a quantified criterion might be a range values or a median value with variation measure. An example a function analysis might be calculation groundwater flow or retention capacity. An example consequences a criterion s not being satisfied might be that site is directly judged to be unsuitable, but might also be that re is a need for a performance assessment, an integrated safety assessment, an integrated construction analysis, or a better body data to judge suitability site. A modified repository layout might also be considered to achieve desired safety functions. For certain already identified suitability indicators, for example those that pertain to indications dissolved oxygen in groundwater at repository level, it is simple to specify clear criteria. For or indicators, such as those that have to do with retention capacity rock, criteria are more complex, since y affect different functions in different ways; y exhibit considerable spatial variability, analysis field data refore ten entails extensive modelling work. The work defining criteria will refore not lead to defined value intervals for all suitability indicators. However, for each indicator it shall be clearly evident how information is dealt with in safety assessment or construction analysis. In cases where defined criteria cannot be specified at parameter level, reason for this shall be given. The term criteria is furr elucidated in Table 3-5, where possible criteria in different stages process leading to a deep repository are specified. Note that criteria at certain stages can also be based on suitability indicators that have not been subject to requirements. This is case, for example, for preferences regarding rmal conductivity rock. Good rmal conductivity is advantageous, this suitability indicator can refore be a basis for a criterion at early siting stages. Satisfaction this preference leads to lower costs, since repository can be made smaller. If preference is not satisfied, however, this can be compensated for by modifying repository layout so that overall safety requirement is neverless met (low rmal conductivity is compensated for by greater spacing between canisters in deep repository) Comparison between sites? It is only in certain cases that criteria can be used directly to compare sites. If requirements are not satisfied on one site, but are on anor, it is obvious that only latter site can be considered for furr studies. To compare sites where both all requirements a large number preferences are satisfied, integrated comparison becomes more complex. The environmental impact assessment, an integrated safety assessment an integrated construction analysis comprise essential background material in integrated assessment wher a site is suitable, see Chapter 2. Replacing integrated assessment with simpler methods, such as weighting points for different parameters, could lead to oversimplification safety assessment construction analysis, re is a great risk that point methods could lead to a misleading result. The criteria presented in report should, however, provide good guidance on outcome integrated assessments. 43

41 Certain criteria, linked to requirements, are so strict that site must be aboned or repository concept substantially modified if criteria are not satisfied. If a site has many properties that lie within favourable value ranges according to criteria, this is a great advantage since it is n very likely that safety assessment will show that safety can be achieved with a wide margin to safety goals. There is no reason to rank sites from a safety viewpoint if safety assessment shows that safety goals can be achieved with a reasonably wide margin on se sites. A furr comparison how sites satisfy safety-related criteria is reby not meaningful. It deserves to be emphasized that it is virtually impossible to formulate criteria that lead to best site. Naturally, all conceivable requirements must be satisfied, a site that has many advantageous properties is probably better than a site with few advantageous properties. What is best in an absolute sense is, however, not self-evident, since many different sets parameter values can lead to same function. When comparing different sites it is also necessary to bear in mind that most rock s properties vary sharply in space that y can only be determined with a given precision. After a selection, as described above, suitable sites in Swedish crystalline bedrock, it will most likely turn out that any differences between suitable sites do not appreciably affect function. Furrmore, difference in many properties will scarcely be statistically significant. 44

42 4 Geology 4.1 Geological conditions that influence function deep repository The description geology an area can be divided into a description soils, rocks deformation zones in rock. Geology determines area s mechanical, rmal, hydraulic chemical properties. The geological information on a site is used primarily as a basis for determining se properties, but re is some geological information that directly influences function deep repository. It is se latter conditions that are discussed in this chapter. The influence on function associated requirements preferences are summarized in Table A.1 in Appendix A Influence on canister integrity Stable geological conditions are needed to ensure mechanical stability canister. The chosen deep repository concept with location in crystalline basement generally satisfies this preference. More specific requirements preferences are mainly derived from discussions rock s mechanical, rmal, hydraulic chemical properties are refore discussed in following chapters (Chapters 5 9). To make sure deep repository is sited in particularly stable areas in rock, repository should be positioned so that disposal tunnels avoid major deformation zones in rock as much as possible. The deformation zones indicate that alterations or movements have taken place at some time in area s geological evolutionary history. The zones usually have reduced strength increased permeability. To obtain a consistent terminology that can be unambiguously understood by representatives all disciplines, SKB uses terms plastic shear zones fracture zones to designate zones where deformation has been plastic brittle, respectively. Sections provide stricter definitions se terms, as well as an analysis what requirements preferences can be made regarding positioning deep repository in relation to different types deformation zones Influence on isolating capacity buffer Stable geological conditions are also desirable so that buffer can retain its isolating sealing capacity. Requirements preferences regarding geological conditions are similar to those that can be derived from requirements preferences regarding how canister function can be ensured (see above). There are no furr requirements preferences, except for more specific requirements preferences regarding mechanical, rmal, hydraulic chemical properties rock (see Chapters 5 9) Influence on isolating retarding capacity rock The deep repository s isolation could be breached if or underground activities are conducted at great depths in repository area in future. The meaning intrusion is dealt with in SR 97. The least acceptable distance depends on scope activities. The likelihood future underground activities is judged to be linked 45

43 to ore potential, occurrence valuable minerals, occurrence unusual rock types assessment or competing interests. Requirements preferences can reby be linked to area s rock type distribution (see section 4.4). In order for rock to have good predictable retention capacity, stable homogeneous geological conditions are desirable. Requirements preferences regarding geological conditions are similar to those that can be derived from requirements preferences regarding how canister function can be ensured (see above). There are no furr requirements preferences, except for more specific requirements preferences regarding mechanical, rmal, hydraulic chemical properties rock (see Chapters 5 9) Biosphere-related matters Biosphere-related matters are dealt with in section Construction-related matters The following principles apply to rock engineering construction facility: working environment shall be safe, environmental impact investigations construction shall be limited kept within acceptable limits, construction shall only have a limited transient impact on safety functions deep repository, construction deposition shall be able to be conducted simultaneously, it is preferable that construction work can be carried out with as few interruptions as possible with limited use extraordinary reinforcement (rock support) sealing measures (good constructability), to facilitate investigations, construction operation, it is preferable that deposition area does not have to be split into a large number subareas that it is possible to position deposition tunnels in a flexible manner. The layout repository is governed to a large extent by geological information. The methodology chosen by SKB configuring repository so that deposition tunnels avoid major deformation zones in rock as far as possible (see sections ) also facilitates achieving above requirements preferences. More specific construction-related matters are discussed in coming chapters, mainly in Chapter 5 (rock mechanics) in Chapter 7 (hydrogeology). 4.2 Topography Description parameter its influence on functions Topography, including or geodetic information, constitutes essential basic information on a site. Detailed topographical information is utilized to identify fracture zones on different scales. The information is refore indirectly essential importance for judging isolating properties rock groundwater flow in rock. 46

44 On a regional scale, topography is ten assumed to provide boundary conditions for groundwater flow in repository area (see furr section 7.6). The bottom topography sea lakes is also importance in assessing influence sea level changes. The topography influences near-surface water flux is refore great importance for conditions in biosphere. The bottom topography lakes watercourses is needed in determination volumes in biosphere models in determination future changes Requirements preferences A small regional topographical gradient is desirable from a hydrogeological point view, since it limits size hydraulic gradient. This preference is discussed furr in chapter Hydrogeology, section Generic knowledge knowledge obtained at different stages According to RD&D-Programme 95 /SKB, 1995a/, topographical gradient normally lies within range 0.1 1% on a regional scale. Higher values occur mainly in Caledonides (mountain range in norrn Sweden). Topographical information can be requisitioned from National L Survey. In conjunction with a site investigation, however, additional data are needed for greater detail. This also applies to bottom topography lakes, watercourses any concerned marine areas Suitability indicators criteria The topography primarily comprises basic information for general geoscientific description can refore not in itself comprise a useful suitability indicator. 4.3 Soils Description parameters ir influence on functions By soils is meant loose deposits that form soil layer on top bedrock. Loose deposits on lake sea beds are also counted as soil cover in this context. The topsoil is uppermost layer soil cover that has been altered by influence wear, vegetation, fauna man. In general, soil cover is limited importance for isolating retarding functions deep repository. The most important functions are that soil cover contributes to oxygen-free conditions in superficial bedrock (by bacterial reduction) that peat mosses, as well as sediments on lake sea beds (mainly clays), can absorb radionuclides. The thickness soil cover, as well as occurrence bottom sediments, also influences boundary conditions for groundwater flow in rock, but this influence is limited indirect importance. Studies soil cover can give indications postglacial movements (neotectonics). The indications may be shoreline displacements or indications occurrence seismites (soils that show clear signs having lost ir bearing capacity on some previous occasion). It is 47

45 essential to determine wher postglacial movements may have occurred in an area. If re are indications such movements, this influences assessment area s long-term mechanical stability. The properties soil cover are included in safety assessment s description transport radionuclides in biosphere (see e.g. SR 97, Main Report, section 9.9 /SKB, 1999a/). The soil cover influences near-surface transport radionuclides, particularly via its capacity to absorb accumulate radionuclides. The aggregate dose consequence depends on many different factors, however, is above all determined by wher release to biosphere occurs at all. It is necessary to be familiar with properties soil cover in order to be able to carry out analysis, but biosphere has no safety function (see Chapter 2) re are reby no grounds for making requirements or preferences regarding properties soil cover from this point view. During a site investigation, soil cover is an obstacle to ascertaining conditions in underlying bedrock from ground surface. The thickness soil cover distribution soil types are also importance for repository layout. Tunnel portals can, for example, be more complicated to execute with thick soil layers. This can influence costs, but is no importance from a safety viewpoint Requirements preferences There are no requirements associated with soil types or thickness soil cover. There are, on or h, several preferences regarding conditions that simplify site investigations. These are that re should be a high proportion exposed rock orwise moderate soil depth (preferably less than about 10 m), since this makes it easier to ascertain conditions in underlying bedrock from ground surface. It is furr an advantage to avoid bouldery waterlogged terrain, clay areas agricultural ls Generic knowledge knowledge obtained at different stages Soil conditions vary widely in Sweden. The dominant soil type in Sweden is glacial till (approx. 75%). There is also a great deal glaciluvial alluvial sediments. Fine sediments have differing origins may be glacial, postglacial or marine. The soil cover frequently shows signs that swelling processes have taken place. Neverless, preferences expressed above are satisfied at a very large number places. Experience from study site investigations shows that extensive thick soil covers present difficulties in continued interpretation work. A feasibility study usually provides a good overall picture occurring soil types ir thicknesses. A detailed picture is obtained from site investigations Suitability indicators criteria Soil type information can be some importance for choosing between sites in stage prior to a site investigation. Special criteria during site investigation are not needed. 48

46 4.4 Rock types Description parameters ir influence on functions In earth s crust, combinations elements form different minerals. Relatively few se minerals constitute main constituents in our most common rock types. Most bedrock in Sweden consists ancient crystalline rock types such as granite, gabbro gneiss. The principles for classifying rock types are complex. For example, designation granite refers to a rock a given mineral composition, while gneiss is a structural term. A gneiss can thus very well have a granitic composition. Requirements preferences regarding rock types are made based on ir properties composition. In each specific case a site investigation, designations used for rocks are defined, along with mineral compositions se rocks. The importance rock types for a deep repository lies mainly in fact that y have different rmal mechanical properties (rmal conductivity, strength, stiffness, etc.). These properties in turn influence constructability rmomechanical influence heated repository, including how heat spreads. Indirect information on strength rock is ten provided by parameters that have to do with rocks grain size, mineral composition mineralogical alteration/wearing. Requirements preferences regarding rock types from this perspective are discussed in Chapter 5 (rock mechanics) Chapter 6 (rmal properties). Differences in strength, structure geological history rocks have led to different fracture systems in different rock types. For example, granites ten exhibit a regular fracture system, while fractures in gneisses are ten controlled by structure rock. In general, rock type boundaries, such as for example boundary between dykes (e.g. diorite) country rock, constitute potential zones weakness in rock. This is because different physical properties rock types also influence ir capacity for deformation to differing degrees. It is refore easier to describe rock if bedrock is homogeneous with few rock types. The fracture system in turn influences or parameters that have to do with strength rock mass groundwater flow through rock mass. Besides variation between rock types, fracture pattern also varies within same rock type between different parts rock mass. Requirements preferences regarding mechanical hydraulic properties fractures are discussed in Chapter 5 (rock mechanics) Chapter 7 (hydrogeology). The rock types also influence composition groundwater. The oxygen in percolating groundwater is consumed by oxidation minerals (see Chapter 8). The minerals can also control ph, Eh or chemical parameters, such as carbonate content, by means different buffering reactions. The difference in rock type composition in crystalline Swedish basement does not, however, give any reason to make special requirements or preferences regarding rock type composition from this aspect. Sorption on fracture-filling minerals can limit mobility radionuclides in rock mass, but influence is limited. In SR 97, it is pessimistically assumed that transport radionuclides is not retarded by sorption in fracture-filling minerals. There are refore no grounds for making requirements or preferences regarding fracture-filling minerals. However, knowledge fracture-filling minerals is essential for building up a geoscientific understing site. 49

47 Figure 4-1. The rock types in repository s deposition area must not have ore potential, i.e. consist such valuable minerals that this could justify mining at a depth hundreds metres. Anor factor to consider is that inhomogeneous bedrock requires greater investigation efforts with more boreholes than a homogeneous one. Certain rock types are interest as natural resources. There may, for example, be acid volcanites, which in many regions are ore-bearing reby unsuitable for a deep repository. Or rock types may be interest for extraction industrial minerals or as utility stone. Since it can be difficult to predict possible uses different rock types in future, it is an advantage if deep repository is sited in commonly occurring rock types, above all granite gneiss. Very high concentrations uranium-bearing minerals may make particularly great requirements on ventilation in repository to keep radon concentration at a sufficiently low level. 50

48 4.4.2 Requirements preferences It is a requirement that rocks in deposition area not have ore potential, see Figure 4-1, i.e. consist such valuable minerals that this could justify mining at a depth hundreds metres. Since it can be difficult to predict possible uses different rock types in future, it is an advantage if deep repository is sited in commonly occurring rock types. Furrmore, it is desirable that bedrock be homogeneous with few rock types, since this simplifies calculations forecasts rmal, mechanical, chemical hydraulic conditions in repository area. For more specific requirements from se perspectives, see Chapters 5 6. It is an advantage if rock contains few minerals that emit radon, but a satisfactory working environment can always be achieved by means various ventilation measures Generic knowledge knowledge obtained at different stages Information on rock type distribution in Sweden is compiled on geological maps published by Geological Survey Sweden (SGU). The information is supplemented in conjunction with regional general siting studies /e.g. Stephens Johansson, 1999ab/. Knowledge principal rock types in superficial bedrock is usually already good at feasibility study stage. Detailed knowledge rock type distribution at greater depth is obtained during site investigations Suitability indicators criteria Rock type distribution is an important suitability indicator, among or things for judging wher repository area meets requirement not having potential for occurrence ore or industrial minerals. Rock type distribution is also used to assess certain mechanical rmal suitability indicators (see Chapters 5 6). The above requirements preferences may be satisfied on a large number sites in Sweden. In regional general siting studies /e.g. Stephens Johansson, 1999ab/, areas are indicated which can be regarded as potentially suitable/unsuitable on a regional scale from this viewpoint, among ors. More detailed knowledge exists in feasibility study municipalities. After completion feasibility study, continued studies investigations are only performed on areas not judged to have potential for occurrence ore or valuable industrial minerals judged to be homogeneous consist commonly occurring rock types. The same criteria are used during site investigation, except that forecast rock type distribution now contains fewer uncertainties. This permits a more local adaptation repository. If extensive occurrence ore-bearing minerals or valuable industrial minerals is encountered, site should be aboned. 51

49 4.5 Structural geology plastic shear zones Description parameters ir influence on functions Over course millennia, bedrock has been subjected to forces temperatures that have partially melted deformed it. Deformation alteration have taken place during certain periods, which have been separated by much longer periods with much calmer geological conditions. The evolutionary process has been fairly complex exhibits regional differences /Larsson Tullborg, 1993/. This deformation has created deformation zones in rock. A deformation zone is a zone weakness in bedrock in which re is considerably greater deformation than in surrounding rock mass. The deformation may have been plastic (see below) or brittle (see 4.6). For a more thorough discussion, see /Bergman et al., 1999/. If temperature pressure have been high enough, deformation has taken place plastically, i.e. without brittle fractures. A large fraction older bedrock in Sweden was deformed plastically between to million years ago. It lay at great depth in earth s crust, up to several tens km, with temperatures up to ºC or more. As a result se deformations, bedrock was folded different linear planar structure (fold axes, schistosity, veining) were formed. The deformations have also resulted in persistent plastic shear zones, which may contain rock type mylonite. If an area is classified as a regional plastic shear zone, this indicates that area has been subjected to heavy deformation, which may in turn have given rise to heterogeneous bedrock. This deformation may have created zones weakness in bedrock in which reactivation under brittle conditions has given rise to water-bearing fracture zones, which may be associated with reduced mechanical strength Requirements preferences In selection areas for site investigations, re is a requirement that regional plastic shear zones be avoided, unless it can be shown that properties zone do not deviate from those rest rock. There may, however, be tectonic lenses in vicinity regional plastic shear zones /SKB, 1997/ where bedrock is homogeneous relatively unaffected. There is no obstacle to siting repository within such lenses, provided y are large enough rock re orwise has suitable properties. See also requirements preferences for fracture zones Generic knowledge knowledge obtained at different stages Knowledge regarding occurrence plastic shear zones is obtained in regional general siting studies (e.g. /Stephens Johansson, 1999ab/) in feasibility studies (e.g. Östhammar /SKB, 1997/). Plastic shear zones are as a rule identified by remote analysis (e.g. aeromagnetic surveys, satellite pictures, etc.) combined with data on planar structures (gneissosity, schistosity) in bedrock. Interpreted zones are verified by geological field mapping. Above all in areas with a high proportion exposed rock, knowledge vertical plastic shear zones is already good at feasibility study stage, while means are not available to find subhorizontal zones. Knowledge is poorer in soilcovered areas, but satisfactory information can ten be obtained from aeromagnetic surveys from regional geological picture. It should be possible to obtain good knowledge plastic shear zones during site investigations. 52

50 4.5.4 Suitability indicators criteria The above discussion shows that information on plastic shear zones is a useful geoscientific suitability indicator. During feasibility study, study site is adjusted so that regional plastic shear zones are avoided. If sufficient repository volume cannot be obtained on remaining area, site is unsuitable. The increased knowledge obtained in site investigation regarding location plastic shear zones properties shear zones is used to devise a site-adapted rock cavern layout. If repository cannot be configured in a reasonable manner, i.e. if it has to be split up into a large number parts, anor site must be chosen. 4.6 Structural geology Fracture zones fractures Description parameters ir influence on functions By fracture zones is meant deformation zones where deformation has been a brittle character, i.e. a mechanical fracturing rocks. Such deformations have occurred higher up in earth s crust where temperatures pressures are lower than in case plastic deformation. Fracture zones generally have a lower mechanical strength a higher permeability than rest rock. The occurrence fracture zones is refore direct importance for rock-mechanical (Chapter 5) hydrogeological (Chapter 7) description a site. Strict classification into brittle plastic deformation zones is not possible, since re are intermediate forms. Furrmore, different names are used for different types deformation zones. A fault is a fracture zone along which movements have taken place. The term lineament is used for an unspecified, topographically /or geophysically distinguishable linear structure in lscape. Nor is terminology consistent in different engineering fields. Words such as structure, zone weakness or discontinuity are ten used to designate fracture zones. To obtain a consistent terminology that can be unambiguously understood by representatives all disciplines, SKB uses term fracture zones to designate all different types deformation zones where deformation has been a brittle character. If only indirect information exists on occurrence a fracture zone, for example a valley or a geophysical anomaly, SKB uses terms lineament or interpreted fracture zone. SKB has furr chosen to classify fracture zones according to length (size) use designations regional fracture zones, local major fracture zones, local minor fracture zones fractures (see Table 4-1). Due to ten complex structure geometry fracture zones, borderlines are somewhat fluid depending on scale purpose investigations. Regional fracture zones major local fracture zones can ten be determined deterministically. By this is meant that locations fracture zones can be established during site investigations. For minor local fracture zones fractures, this is not possible in entire rock mass surrounding a repository. Instead, statistical descriptions ir locations properties are used. Interpreted fracture zones ten have to suffice for regional groundwater models. 53

51 Table 4-1. Classification naming bedrock s brittle structures, ambition level for geometric description during site investigation (length width measurements are approximate). Name Length Width Ambition for geometric description Regional fracture zones > 10 km > 100 m Deterministic Local major fracture zones 1 10 km m Deterministic (with uncertainties) Local minor fracture zones 10 m 1 km m Statistical (some deterministic) Fractures < 10 m < 0.1 m Statistical The length classification does not in itself constitute a ground for fracture zones different sizes having different properties. To characterize a fracture zone, information is needed on its location, orientation, length width, but also on its properties. The mechanical hydraulic properties fracture zones fractures is furr discussed in sections The regional local major fracture zones have ten been formed in connection with primary plastic zones. They are usually characterized by heavy schistosity with a high fracture frequency or by locally crushed, sometimes clayaltered sections. From a mechanical viewpoint, larger future deformations can generally be expected in large (long) fracture zones than in small (short) ones (SR 97, Process Report /SKB, 1999b/). Large fracture zones are furrmore usually more permeable than surrounding rock, although re are individual fractures that are at least as water-bearing as major fracture zones. Information on fracture zones fractures is used directly to configure a layout for deep repository. The work is done in steps. Corridors for access transport tunnels volumes for deposition area are determined during site investigation. The direction deposition tunnels is determined. However, a detailed layout in terms e.g. exact coordinates for each deposition hole does not have to exist until exact locations deposition tunnels have been determined. This is not done until during detailed characterization stage or during repository construction. In future studies, SKB will take into account whatever detailed information on individual fractures minor fracture zones is obtained from investigations for development investigation, transport disposal tunnels in order to progressively refine layout repository position individual deposition holes. In safety assessments performed to date (e.g. SR 97), no credit is taken for this potential for improving repository layout by detailed adaptation layout to actual conditions Requirements preferences To avoid placing deposition holes in areas where re is a high risk future deformations high permeability, it is a requirement that deposition tunnels deposition holes may not pass through or be located near regional local major fracture zones, see Figure 4-2. This requirement does not apply to fracture zones that have been found to be mechanically hydraulically similar to surrounding rock. The requirement does not apply to access tunnels transport tunnels. It is a requirement that deposition holes should not intersect identified local minor fracture zones. It is refore preferable to have a moderate density (fracture surface area per volume) fractures local minor fracture zones. 54

52 It is not possible to stipulate general requirements on smallest acceptable distance between deposition tunnels regional or local major fracture zones. The groundwater flow through repository mechanical stability repository are dependent on properties fracture zone surrounding rock, which means that mechanical hydrogeological function always need to be evaluated for a particular layout. When devising repository layouts, however, SKB will use respect distances between deposition tunnels identified regional local major fracture zones. The respect distances are composed a distance judged to comprise a suitable minimum distance between tunnel fracture zone, plus a safety margin that compensates for fact that location fracture zones is not completely known. The judgement what a suitable distance between tunnel fracture zone is, as well as size safety margin needed to manage uncertainty in location fracture zones, are dependent on level knowledge rock reby have more character criteria than strict requirements preferences. The size respect distances is refore discussed under heading criteria below. Assumed respect distances will be used in conjunction with stepwise site investigation design process (see below). But real distances that are needed are determined by means a site-specific function analysis. Figure 4-2. Deformation over course millennia has created deformation zones in rock. A deformation zone is a zone weakness in bedrock in which deformation is much greater than in surrounding rock mass. The deformation may have been plastic or brittle (fracture zones). It is a requirement that deposition tunnels deposition holes may not pass through or be positioned too close to regional local major fracture zones. 55

53 4.6.3 Generic knowledge knowledge obtained at different stages The occurrence regional local major fracture zones has been mapped with varying accuracy in different parts country. More targeted studies are conducted in conjunction with regional general siting studies /e.g. Stephens Johansson, 1999ab/. Fracture zones for sites analyzed in SR 97 are described by Rhén et al. (1997), Andersson et al. (1991) Hermanson et al. (1997). Saksa Nummela (1998) discuss uncertainties in se descriptions. The material that is available in a feasibility study permits a preliminary identification regional fracture zones. The forecast is improved if degree exposure is high (see section 4.3.4). Interpreted zones are verified by geological field mapping. Above all in areas with a high proportion exposed rock, knowledge vertical plastic shear zones is already good at feasibility study stage, while means are not available to find subhorizontal zones. Knowledge is poorer in soil-covered areas, but satisfactory information can ten be obtained from aeromagnetic surveys from regional geological picture. The ambition level in site investigations is to describe all regional local fracture zones deterministically, while local minor fracture zones individual fractures can normally only be described statistically. The probability that re are undiscovered major fracture zones in area also needs to be estimated Suitability indicators criteria Information on fracture zones discrete fractures constitutes an important suitability indicator. Cidate areas for furr investigations are chosen in a feasibility study so that a deep repository can be positioned with good margin to fracture zones identified in feasibility study. Even though this can (almost) always be achieved by splitting repository up into different parts, it is obviously desirable that repository not have to be split up into too many parts. Available data must not indicate that fracture zones are so dense that repository would have to be split up into an unreasonably large number parts. Possible investigation areas may only be intersected by a few regional fracture zones. During site investigation, hypotical repository is adapted to nidentified zones. Suitable respect distances to identified regional local major fracture zones can only be determined site-specifically, but are assumed to comprise at least several tens metres to local major zones at least 100 metres to regional zones. Information on mechanical hydraulic (permeability) properties zones adjacent rock mass is utilized. Depending on properties fracture zones rock mass, this may necessitate increasing distance to certain zones, while distance to or zones may be decreased. The above guidelines for respect distance will, however, be used in initial layout work. If repository has to be split up into a very large number parts, site is not suitable for a deep repository. It should furr be noted that information on fracture zones individual fractures is essential for analysis site s rock-mechanical (see 5.4) hydrogeological (7.2) conditions. 56

54 4.7 Summary suitability indicators geology The preceding sections have provided an account which geological suitability indicators may be relevant in different stages siting work. The complete account work is found in Tables A-1 in Appendix A B-1 in Appendix B is summarized in Table 4-2. Table 4-2. Suitability indicators for geology ( complete account is found in Appendices A B) Parameters Requirements or preferences Criteria during feasibility study (FS) groupwise during site investigation (SI) Topography Important basic information, but not primary indicator. See hydrogeology. Soils Preference: small thickness FS: high proportion exposed rock. SI: Not relevant during site investigation. Rock types Requirement: no ore potential. FS: Avoid areas with known ore potential Preferences: no valuable utility stone or heterogeneous or unusual bedrock. industrial minerals, common rock type. (Indirect requirements/preferences from SI: Local adaptation repository with referrock mechanics hydrogeology). ence to indicator. If extensive occurrence ore-bearing minerals is encountered, site should be aboned. Plastic Regional plastic shear zones are avoided, FS: Avoid known regional plastic shear shear zones if it cannot be shown that properties zones. If sufficient repository volume cannot zone do not deviate from those be obtained, anor area must be chosen. rest rock. There may, however, be tectonic lenses near regional plastic shear SI: Revise layout according to new knowzone that can be suitable for a deep ledge. If repository cannot be positioned repository. in a reasonable manner (if it would have to split up into a very large number parts), anor area must be chosen. Fracture zones Deposition tunnels holes may not FS: Choose area for continued studies so pass through or be located near regional that a deep repository can be positioned local major fracture zones. Assumed with good margin in relation to fracture respect distances will be used in conjunction zones identified in feasibility study. The with stepwise site investigation area is unsuitable if known fracture zones design process. But distances that are so dense that a repository would have are really needed are determined via a to be split up into an unreasonably large site-specific function analysis. number parts. Deposition holes may not intersect identified local minor fracture zones. Moderate densities (fracture surface area per volume) fractures local minor fracture zones are also preferable. SI: Suitable respect distances to identified regional local major fracture zones can only be determined site-specifically but are assumed to comprise at least several tens metres to local major zones at least 100 metres to regional zones. If repository cannot be positioned in a reasonable manner (would have to be split up into a very large number parts) in relation to plastic shear zones, regional fracture zones or local major fracture zones, site is not suitable for a deep repository. 57

55 5 Rock mechanics 5.1 Influence on function deep repository The mechanical properties rock influence both isolating retarding functions deep repository. The rock-mechanical properties are also great importance for how repository is configured constructed. Generally speaking, technical conditions for constructing rock caverns in Swedish crystalline basement are good. Table A-2 in Appendix A summarizes how mechanical properties rock influence functions deep repository, what requirements preferences can be derived from this Overview The rock is a mechanical system that is normally in static equilibrium under prevailing loads. Disturbances this equilibrium may be caused by load changes, e.g. due to excavation rock caverns, or by changes in mechanical properties rock. Instability leads to deformation rock mass, failure can occur if strength rock is exceeded. The failure state as such does not have to entail serious instability, however: small deformations, without consequences for performance safety, can be sufficient for system to regain equilibrium if failure should occur. The mechanical disturbances take place during different epochs in different parts rock. The disturbances also take place on different scales: firstly, re are different problem scales such as deposition holes, tunnels, entire tunnel system, rock volume around repository; secondly, disturbances can cause both small-scale large-scale changes. The geometric distribution fracture zones rock types ir mechanical properties determine where deformation possible failures will occur. Movements take place preferably along fractures fracture zones. Furrmore, different rock types have different strengths different deformation properties. The rock extraction that takes place during repository construction leads to an extensive change in mechanical equilibrium, which leads to stress redistribution deformations around tunnels. If stress levels are high relative to strength rock mass, local failure can occur. This can occur rapidly in brittle rock types is called spalling (stress induced failure). Furrmore, structurally induced failure occur when loose rock blocks fall out due to fracture geometry, stress situation mechanical properties fractures rock. The conditions for construction in rock are refore associated with a number construction-related requirements preferences. The safety assessment is based on initial state where repository s tunnels are built. The disturbances associated with rock extraction civil engineering activities refore have only an indirect influence on repository safety. Deposition will only take place in tunnels that have been excavated in a satisfactory manner. Changes in geometry deposition holes could damage buffer or canister. Extensive movements along fractures fracture zones, or extensive formation new fractures, could degrade retention properties rock. The load cases that need to be taken into account are mainly changes in pore pressure on resaturation, swelling 59

56 pressure from bentonite, rmal expansion rock, effects earthquakes effects extensive climate change (such as glaciations). Furrmore, it is necessary to take account fact that mechanical properties rock can change with time. Such changes in near-field rock may be reduced friction or cohesion in fractures, loosening due to increased loading, or fact that rock supports installed to stabilize tunnel during construction operation deteriorate with time (e.g. corrosion in rock bolts). For a more thorough analysis how rock-mechanical processes influence repository safety, see SR 97 Main Report Process Report /SKB, 1999ab/ Influence on canister integrity If deposition holes are deformed too much, canister could be damaged. Calculations with a previous, less deformation-resistant design canister /Börgesson, 1992/ showed that rock movements on order 0.1 m do not lead to immediate canister failure. The canister design analyzed in SR 97 can take greater loads, so this canister should withst greater deformations deposition hole. On or h, it is concluded in SR 97 Main Report /SKB, 1999a/ that due to various uncertainties in assessment (creep deformation copper canister, velocity rock movement, etc.) pessimistic criterion should be used that rock movements on order 0.1 m or more could lead to canister damage. This criterion could naturally be changed with furr changes in canister design or design deposition hole. The fundamental conditions that are advantageous or less advantageous for mechanical stability repository are, however, not altered by minor changes in repository design. It is course desirable that re be as little deformation as possible. In practice, this stability requirement is hled by not locating deposition holes too close to large fracture zones. There is also a discussion in SR 97 Main Report /SKB, 1999a/ wher deposition holes could in long term be deformed by creep movements in bedrock. Such movements could occur if mechanical properties host rock change with time so that movements take place due to already active stresses. The changes may be directly dependent on state stress, i.e. unstable growth micrractures in intact rock. Uneven distribution shear stresses along fracture planes on all scales can lead to initiation growth micrractures eventually to local plasticization in connection with stress concentrations at irregularities in fracture surfaces. Knowledge is poor, but attempts that have been made to analyze process have indicated slow processes small deformations Influence on isolating retarding capacity buffer To preserve isolating retarding capacity buffer, deformation deposition holes may not cause damage to buffer. Such damage could only be caused by large deformations /Pusch Börgesson, 1992/. Fracturing that gives rise to cavities around deposition hole could also cause erosion bentonite. Deformations may not create such large cavities around deposition hole that buffer could swell without confinement thus loose its swelling pressure. Nor may deformations deposition hole (instantaneous or cumulative) be so large that diffusion distance through buffer becomes too small. The mechanisms that could lead to deformations deposition hole have already been discussed in previous sections. 60

57 The fractures that intersect deposition hole can, toger with hole wall, form loose blocks called wedges. If an overbreak occur, special measures are required to fill spaces where blocks were with bentonite. Block breakout is refore not desirable, extensive block breakout will make deposition hole unusable. Similar problems can arise if induced stresses on boundary deposition hole exceed compressive strength rock Influence on retarding capacity rock If fractures ( fracture zones) are deformed, ir permeability changes because fracture aperture changes. Formation new fractures also affects permeability. Except in immediate vicinity repository, however, se changes can be expected to be relatively small compared to initially already very large spatial variation in permeability fractures. There are no mechanical requirements on isolating retarding functions rock. It is, however, desirable that deformation rock mass fracture zones should lead to negligible changes in permeability in relation to or uncertainties. This preference applies both on a local scale, around deposition hole, on larger scale that represents rock between deposition hole major fracture zones. Disturbances that influence permeability on a deposition hole scale can, in principle, occur for all conceivable load cases (see above), while disturbances that affect rock on a larger scale could be caused by temperature changes external loads caused by e.g. earthquakes or glaciations Construction-related matters The repository is configured so that probability damage to repository due to large deformations faults is minimized. There are furrmore several rockmechanical questions that must be taken into account in conjunction with construction operation: All requirements on personal safety must be satisfied. Extensive rock burst, or major overbreak collapse must generally be avoided. Extensive stability problems cannot be accepted in deposition tunnels or deposition holes, since this would prevent ir being configured as planned. It is preferable that civil engineering works can be carried out with as few complications as possible. (Potential reinforcement needs, downtimes etc. are investigated in conjunction with design process.) If repository area has to be split up into many subareas, separate investigations may be required regarding possibilities passing through fracture zones that separate areas. The above requirements preferences can as a rule be satisfied by means a suitable repository layout, choice siting depth choice execution methods. Due to increasing rock stress levels with increasing depth, constructability is much poorer at great depths /Winberg, 1996/. The repository layout is adapted to regional local major fracture zones (see sections ) to assessments how tunnels should be oriented in relation to rock properties states stress (see e.g. /Munier et al., 1997/). 61

58 For design process, information is needed on a variety parameters to choose suitable execution methods to be able to plan work. If full-face tunnel boring is chosen, properties such as penetration index, drilling rate index (DRI) wear properties should be determined. Furrmore, stress-induced failures in tunnel contour can influence feasibility carrying out tunnel boring. Blastability should be assessed when choosing blasting method explosive. None se parameters are important for choice site, but can affect construction costs. 5.2 Initial rock stresses Description parameters ir influence on functions The state stress in rock is a variable for all mechanical processes. The state stress is a tensor is characterized by three mutually perpendicular principal directions, each which corresponds to a principal stress. If all three principal stresses are equal, state stress is isotropic principal directions are indefinite. If principal stresses are unequal, state stress is anisotropic (deviatoric). The stability rock-mechanical system is dependent on stress conditions. Besides providing boundary conditions support for rock-mechanical analysis, knowledge initial in-situ stress distribution indirectly furnishes information on stability rock. High deviatoric stresses complicate above all execution rock works, since it is in this stage that great changes take place in stress field around tunnels deposition holes. Moderate rock stresses in tunnel periphery have a stabilizing effect. Excessively high or deviatoric tangential stresses in tunnel periphery in relation to strength intact rock can, however, cause spalling phenomena or contribute to or types overbreak. The magnitude direction initial stress field reby directly influences what are suitable tunnel directions choice rock excavation methods Requirements preferences It is a requirement that extensive spalling phenomena or or extensive rock breakout not occur within deposition area, since this can make it impossible to construct durable deposition holes (Figure 5-1). This requirement is mitigated outside deposition area, here it is also possible to reinforce rock, which can scarcely be done directly in deposition holes. Function is verified by a site-specific rock-mechanical analysis, where resultant stress situation around tunnels is forecast. The initial stress distribution is included in such an analysis, but it is not possible to directly stipulate requirements on initial stress distribution. It is generally an advantage if initial stresses do not deviate from what is normal in Swedish bedrock (i.e. well below 70 MPa) are as isotropic as possible at planned repository depth Generic knowledge knowledge obtained at different stages There is some generic knowledge initial rock stress distribution. The vertical stress is as a rule approximately equal to weight overlying rock mass reby increases with depth. At a depth 500 m, vertical stress is normally about 14 MPa. The greatest horizontal stress at this depth lies in range MPa /Stille Nord, 1990/. 62

59 Less scaling damages. Microseismic events with magnitude 2 to 1. Elastic response Less scaling. Microseismic events with magnitude 6 to 2. Uniaxial compressive strength Data from Hoek Brown Äspö level 420 level 420 Maximum initial rock stress Serious scaling damages. Seismic events with magnitude 1 to 2. Serious damage. Seismic events with magnitude 2 to 4. Figure 5-1. Empirical stability classification developed for mine drifts rectangular cross-section in South Africa. Modified by /Martin et al., 1999/ from /Hoek Brown, 1980/. The figure is supplemented with data from Äspö Hard Rock Laboratory (HRL) Underground Research Laboratory (URL) in Canada. It is a requirement that extensive spalling phenomena or or extensive rock breakout do not occur within deposition area. Previous experience from underground projects in area is collected in feasibility studies. Experience from underground construction (see e.g. feasibility study in Östhammar /SKB, 1997/) shows, however, that large local variations ten occur that investigations on a specific site with boreholes to intended depth are necessary so that any local problems will be revealed reliable construction-related assessments can be made. In site investigation, initial stresses can be measured in boreholes by e.g. overcoring hydraulic fracturing. However, uncertainties spatial variation are relatively great /Ljunggren et al., 1998/. Additional stress measurements can be made from boreholes at repository level during detailed characterization repository construction Suitability indicators criteria Initial rock stresses are obviously useful as suitability indicators, partly for ir importance in choice facility layout partly because y are included in an analysis stability conditions during construction operation. 63

60 There are no grounds for issuing criteria based on knowledge from feasibility studies or than general evaluations that are made within framework feasibility studies. A qualified site-specific rock-mechanical analysis shall be carried out during site investigation where future stress situation in rock surrounding tunnels resulting rock stability during after construction phase are forecast. The input values in analysis are tunnel geometry estimated (during site investigation) values geometric distribution strength deformation properties intact rock, geometry deformation properties fracture system, initial rock stresses. Since function is dependent on many interacting factors, a specific criterion for acceptable initial stresses cannot be set up. Furrmore, uncertainties in rock stress measurements have to be taken into account. If drill core cracks up into discs ( core discing ) it is a strong indication high stress levels. Extensive problems with core discing should refore give rise to suspicion that problems may be encountered with spalling during tunnelling. The analysis is used mainly to adapt siting depth layout (reinforcements, tunnel geometry, alignements) to prevailing conditions. If repository cannot be reasonably configured in such a way that extensive general spalling problems are avoided, site is unsuitable should be aboned. 5.3 Mechanical properties intact rock Description parameters ir influence on functions By intact rock is meant in rock-mechanical contexts rock without visible fractures. As a rule, deformation properties intact rock are described with a linear portion, in form modulus elasticity (E) Poisson s ratio (n), a plastic portion which is dependent on strength material. Furr parameters occur in some material models. The stability rock-mechanical systems is dependent on stress conditions. Idealized relationships, failure criteria, give dependence as a function principal stresses. However, fracturing process in fact starts at lower loads than actual failure load. Rock in a state stress equivalent to approximately 80% failure load may, without furr load increase, be fragmented after some time if stress level is retained /Martin, 1994/. The phenomenon can be observed at great depth where primary stresses are high where rock extraction to create tunnels or types cavities gives rise to large stress concentrations. Next to cavity walls, tangential stresses are large radial constraint small, which can lead to rock breakout due to fracturing parallel to cavity wall ( splitting failure ). If splitting failure is violent, a type rock burst has occurred. The mechanisms that control growth micrractures in principle also control propagation existing fractures. In constrained rock, an individual fracture can propagate by spreading in its own plane by means shear failure, by fracturing at an angle to its own plane by tensile failure at periphery fracture, so-called splay cracks /Scholz 1990/. 64

61 For choice tunnelling methods in conjunction with rock engineering, properties such as penetration index, DRI (drilling rate index), wear properties blastability need to be determined. These parameters are no importance from viewpoints safety or siting. They are used in design work for rock excavation Requirements preferences See section for formulation requirements. It is a preference that intact rock should have strength deformation properties that are normal for Swedish bedrock, since experience has shown that it is possible to carry out rock excavation works with good results in such bedrock. Furrmore, it is a preference that strength rock should have margin to cope with stress redistribution that takes place with chosen tunnel design due to rmal expansion rock due to heat in deposited canisters Generic knowledge knowledge obtained at different stages There is good generic knowledge mechanical properties intact rock /Stille Nord, 1990/. As a rule, intact rock in Swedish crystalline basement has a modulus elasticity between GPa, a Poisson s ratio between , a compressive strength between MPa a tensile strength between 2 10 MPa. The feasibility study s assessment which rock types occur furnishes additional information, since strength varies with different rock types. Site-specific information can be obtained from mapping, classification tests on drill cores retrieved in conjunction with site investigation. The detailed characterization furnishes more direct knowledge on intact rock located close to tunnels deposition holes. The parameters blastability, penetration index, DRI wear properties are used generally in construction analysis to estimate construction costs, as well as in detailed engineering stage. None se parameters influence choice site Suitability indicators criteria The compressive strength intact rock is a useful suitability indicator, but cannot be used in isolation to judge risk extensive spalling or or extensive overbreaks. The rock type assessment that can be made during a feasibility study furnishes a general basis for determining strength deformation properties intact rock. The difference in properties between rock types that are suitable for hosting a deep repository is, however, relatively limited. For criteria during site investigation, see section

62 5.4 Fractures fracture zones Description parameters ir influence on functions The occurrence fractures fracture zones is great importance for mechanical properties rock. Compared with rock without visible fractures, strength stiffness fractures is small in plane fractures zones. Moreover, fractures fracture zones have negligible tensile strength perpendicular to fracture plan. Stiffness against displacements in plane fracture/zone limits its persistence. Large (persistent) fracture zones have greater prospects being displaced than small ones. Fractures can be deformed perpendicularly to plane fracture (normal deformation) or in plane fracture (shear deformation). If stress varies perpendicularly to plane fracture, fracture may open or close. The relationship between normal stress normal deformation is usually described by normal stiffness /see e.g. Barton et al., 1985/. Fractures can also be deformed in plane fracture shear movements. Shear failure occurs when load is too high. The shear strength fracture is dependent on, among or things, size normal stress across fracture (friction). If ratio between shear load normal stress exceeds a given value ( friction angle ), friction is not sufficient to prevent a movement. The size movement is, however, also determined by size fracture /Turcotte, 1992/. Deformation is small for short fractures, even if friction is neglected. Normal deformations lead to a change in fracture aperture. This also changes permeability fracture. Shearing along non-planar fractures can cause aperture variations due to roughness waviness fracture. This also leads in turn to changes in permeability fracture. This hydromechanical coupling is, however, relatively limited importance for long-term safety, although it may need to be taken into account in evaluation hydraulic tests (e.g. /Rutqvist et al., 1996/). The deformation properties individual fracture are some importance for assessing mechanical stability in a rock cavern. It is generally an advantage if fractures have a high friction angle, since this furr increases rock stability. Stability is determined essentially by arch formation, risk overbreak wedges, occurrence rock bridges intact rock. For mechanical assessment it is chiefly geometry (direction) tunnel geometry (direction) fractures in relation to directions stress fields future changes in m that are importance, but high friction in fractures contributes to increased stability Requirements preferences In order to ensure that deposition holes are not deformed in a manner that could damage canister, it is a requirement that deposition holes not be allowed in or near regional or local major fracture zones (see furr discussion in section 4.6). The geometry local minor fracture zones individual fractures is also great importance for wher deposition holes can be deformed. Individual deposition holes are not to be positioned so that y intersect minor fracture zones. The individual fractures are also importance, but function analyses with a mechanical model that have been done within framework SKI project SITE-94 /Hanson et al., 1995/ could not find any case where deformation deposition hole exceeded 0.1 m. The adaptation repository layout to geometry fracture network is direct importance for impact seismic events, see /LaPointe et al., 1999/. However, 66

63 it is not possible to stipulate requirements or preferences regarding geometry fractures or fracture zones; instead, resulting function needs to be analyzed. There are no grounds for stipulating exact requirements or preferences regarding how deformation properties fractures influence permeability. From a rock excavation point view, a suitable positioning, layout reinforcement tunnels is chosen on basis prevailing fracture frequency, fracture geometry rock stresses. Fracture geometry fracture angles should also be such that quantity overbreak in deposition holes (see section 5.1.3) is not too great. However, it is not possible to stipulate more exact preferences regarding geometry here eir; instead, an assessment must be made from case to case. From viewpoint stability during construction, it is also desirable that friction angle fractures not be too small. A high friction angle is also advantageous for long-term safety, but friction angle is not decisive for mechanical stability repository Generic knowledge knowledge obtained at different stages See section 4.6 regarding geometry fractures fracture zones. There is good generic knowledge mechanical properties fractures /Stille Nord, 1990/. A feasibility study does not in itself furnish any new information. Site-specific information can be obtained by performing laboratory tests on fractures in drill cores retrieved in conjunction with site investigation. In view limited importance information, however, a large number measurements are not needed. Detailed characterization provides more direct knowledge on individual fractures located close to tunnels deposition holes Suitability indicators criteria The occurrence geometry fracture zones are obviously useful as suitability indicators from a rock-mechanical viewpoint as well. In order to be able to judge wher requirements or preferences are satisfied for a given fracture geometry, however, it is as a rule necessary to carry out a specific mechanical analysis to assess risk block breakout. However, such an analysis can, in simple cases, be carried out with geometric information alone. Criteria for adaptation repository to known fracture zones are discussed in section It is not meaningful to carry out a quantitative rock-mechanical analysis with information that is available after a feasibility study. After a site investigation, location most regional local major fracture zones should be known. If ir frequency is so high that repository cannot be positioned without being split up into a very large number parts, site is unsuitable. Mechanical properties fractures particularly need to be assessed for detailed characterization repository construction. The mechanical properties fractures are refore less useful as suitability indicators, even though it is preferable that fractures with extremely low friction not occur within repository area. The laboratory tests on drill cores that can be done during a site investigation reveal properties on a centimetre scale. These values are needed to build up geoscientific understing site can furrmore be used in construction analysis (e.g. for assessment reinforcing needs). Conservative assumptions (frictionless 67

64 cohesionless fractures) are as a rule made in safety assessment. Owing to small importance preferences large measurement problems, re is no reason to stipulate criteria, not even during site investigation. 5.5 Mechanical properties rock mass as a whole Description parameters ir influence on functions In connection with practical rock-mechanical modelling stability on a repository scale, only major fracture zones are modelled explicitly, n as a rule as zones with deviant strength properties. The rock, both in fracture zones in between, is denoted by term rock mass, which represents strength properties for non-explicitlydescribed fractures intact rock toger. The concept rock mass must be related to scale on which rock is described. In rock-mechanical analysis normally carried out by SKB, regional local major fracture zones are described explicitly are refore not included in rock mass. In more detailed discrete analyses, local minor individual fractures can also be described explicitly, albeit stochastically. The intervening rock corresponds to intact rock in this latter case. It is not customary to stipulate values strength rock mass. If failure occurs in rock mass, it occurs in most cases due to a complex combination failure in intact rock deformation/failure in fractures. An exact description failure process is seldom possible; instead, empirical failure criteria classifications rock mass, such as Q system /Barton, 1974/ or RMR system (see e.g. /Brady Brown, 1993/), are normally used to determine if re is a risk problems. The empirical classification methods can be used as a basis for designing rock support /National Road Administration (1999)/, but are open to criticism for providing a oversimplified picture complex processes relationships. Empirical classifications can be used as tools in ongoing design work, but constructability is verified by means rock-mechanical analyses Requirements preferences It is not meaningful to stipulate requirements on rock mass. From constructability viewpoint in particular, re are preferences that rock mass which includes local minor fracture zones, individual fractures intact rock should have a strength that is at least on a par with normal conditions in Swedish bedrock Generic knowledge knowledge obtained at different stages There is good generic knowledge mechanical properties rock mass. Previous experience from underground projects in area is collected in feasibility studies. Experience from underground construction (see e.g. feasibility study in Östhammar /SKB, 1997/) shows, however, that large local variations ten occur that borehole investigations on a specific site to intended depth are necessary so that any local problems will be revealed reliable construction-related assessments can be made. 68

65 Site-specific information on properties rock mass can be obtained by logging classification drill cores retrieved in conjunction with site investigation. The detailed characterization furnishes more knowledge, above all direct experience gained from building in rock in question Suitability indicators criteria In view above preferences, strength rock mass is a useful suitability indicator. The requirement on precision in determination is, however, limited, in analyses based on site investigation data, sensitivity analyses for known extreme values will primarily be carried out. There are no grounds for issuing criteria based on knowledge from feasibility studies or than general evaluations that are already made within framework feasibility studies. The forecast properties rock mass that is made in conjunction with site investigation is utilized for repository layout for constructability forecast. The constructability forecast is included in total comparison material between sites, but has no direct safety-related importance. Good constructability is course advantageous. 5.6 Coefficient rmal expansion Description parameter its influence on functions The coefficient rmal expansion is a measure change in volume rock due to a change in temperature. The coefficient rmal expansion, toger with heat transport data (rmal conductivity specific heat), comprises model data in calculation stress changes deformations that occur due to rmal load. Since rock in repository is constrained, expansion is completely or partially suppressed, rmal stresses are generated in rock mass surrounding deposition holes repository. The size volume expansion rmal stresses is dependent on coefficient rmal expansion deformation properties rock. Due to heat production in repository, special attention must be given to threat that tensile stresses might arise at great depth. Around individual deposition holes, it is important that rmal expansion be sufficiently even. The coefficient rmal expansion is dependent on mineral composition rock, although variations between different rock types are not great. Initial analyses have been made by Hökmark (1996). The rmal displacements as such have no direct bearing on safety. However, rmal load contribution can, toger with loads that already exist in initial state, cause strength intact rock fractures to be exceeded. This needs to be checked in a site-specific function analysis, but does not entail direct requirements or preferences regarding coefficient rmal expansion. 69

66 5.6.2 Requirements preferences There is no reason to make requirements on coefficient rmal expansion within range variation that is possible in a crystalline bedrock. It is preferable that parameters have normal values for Swedish bedrock (within range 10 6 to 10 5 K 1 ) that y do not differ much between rock types that exist in repository area Generic knowledge knowledge obtained at different stages The probable value range for coefficient rmal expansion in Swedish crystalline bedrock is between K K 1. There is good generic knowledge value coefficient rmal expansion. A feasibility study can provide some idea which types rock occur at depth. But it is not until site investigations that samples drill cores obtained during site investigations can provide a more accurate picture rock type distribution within repository area. The detailed characterization provides more direct knowledge in areas located close to tunnels deposition holes Suitability indicators criteria The coefficient rmal expansion is not a primary suitability indicator, but needs to be determined during a site investigation. The coefficient is necessary to know for a rmomechanical analysis, but values within above value ranges can be used. Any preferences on a deposition hole scale can be hled during repository construction in connection with selection deposition holes. A rough mineralogical description is obtained during feasibility study, but rock type inhomogeneities can only be judged in general terms from surface characterization. Highly inhomogeneous conditions on surface do, however, warrant more thorough characterization during site investigation. The more detailed knowledge obtained from drill cores during a site investigation does not provide grounds for quantitative criteria eir. If rock is very heterogeneous, more extensive investigations are required. A rmomechanical analysis needs to be done in any case, but its results are dependent more on fracture geometry initial stress conditions. 5.7 Future loads Description parameters ir influence on functions Future external events could affect mechanical stability rock. The effects earthquakes future ice ages in particular were studied in SR 97 /1999a/. Seismic activity during next 100,000 years was estimated in seismic analysis carried out within framework SR 97 /La Pointe et al., 1999/ by extrapolating from present-day seismic activity. This estimate (frequency magnitude) is included directly in analysis. According to analysis, only earthquakes with a magnitude 70

67 greater than about 7 that occur in fracture zones in immediate vicinity repository can cause deformations large enough to damage canister. Such large earthquakes can, on or h, only occur in regional fracture zones, which will be avoided in locating repository. Furrmore, analysis exaggerates consequences, since it is assumed that shear deformation fractures is not hindered by friction in plane fracture. In or words, analysis is based on several pessimistic assumptions. In analysis a glaciation scenario, mechanical effects ice sheet are studied. No fracture movements large enough to damage canisters have been obtained for load cases analyzed so far in numerical models /e.g. Hansson et al., 1995/. For or reasonable static load cases as well, judgement can be made that no shear movements in fractures intersecting canister hole positions will be large enough to damage canister (see SR 97, Main Report, Chapter 10 /SKB, 1999a/) Requirements preferences It is obviously advantageous if future seismic activity is low magnitude occurs at low frequency. The regional differences that exist in different forecasts are, however, too small in relation to uncertainties. Both ice age earthquakes belong to scenarios that are analyzed within framework a safety assessment, but analyses have little coupling to choice site. Because layout repository is adapted by not allowing deposition holes to intersect local minor fracture zones (see 5.4), risk earthquake-induced damage is also minimized Usefulness as suitability indicators The forecasts future earthquakes ice ages analysis consequences if y occur must be done within framework a safety assessment. The safety assessment SR 97 /SKB, 1999a/ is based on pessimistic assessments scope se events. In view uncertainties, however, it is not reasonable to use forecasts future seismic activity or forecasts future ice ages as suitability indicators. 5.8 Summary suitability indicators rock mechanics The preceding sections have provided an account which rock-mechanical suitability indicators may be relevant in different stages siting work. A complete account this work can be found in Table A-2 in Appendix A Table B-2 in Appendix B. As is evident above, suitability indicators are mainly used to assess wher requirements preferences are satisfied. Table 5-1 provides a compilation suitability indicators that have been preliminarily identified for rock mechanics. 71

68 Table 5-1. Suitability indicators for rock mechanics ( complete account is found in Appendices A B). Parameters Requirements or preferences Criteria during feasibility study (FS) groupwise during site investigation (SI) Initial Extensive spalling or or extensive FS: No criteria rock stresses overbreak may not occur within a large portion deposition area. SI: Calculated stress situation in rock nearest Function is verified by means a tunnels resultant rock stability during site-specific analysis. after construction phase is used mainly to adapt repository depth layout. If repository Preference for normal (considerably cannot be reasonably configured in such a way lower than 70 MPa) initial stresses that extensive general spalling problems can be at repository depth. avoided, site is unsuitable should be aboned. Extensive problems with core discing should directly give rise to suspicion that problems may be encountered with spalling during tunnelling. Intact rock Extensive spalling or or extensive FS: Assessment based on preliminary rock type (E, ν, rock breakout may not occur within forecast may not indicate unfavourable conditions. compressive a large portion deposition area. strength etc.) SI: Special attention if strength rocks It is preferable that intact rock deviates strongly from normal values in Swedish have strength deformation bedrock. See also initial rock stresses. properties that are normal for Swedish bedrock. Fractures For adaptation to geometry FS: For adaptation to geometry fracture zones fracture zones fracture zones fractures fractures see geology. see geology. SI: For adaptation to geometry fracture zones Tunnel layout/location is chosen based on stresses fracture directions. Large friction angle suitable. fractures see geology. Rock-mechanical analysis function (see intact rock above.) Rock mass No requirements FS: No criteria as a whole Properties at least on a par with SI: The forecast properties rock mass normal conditions in Swedish that is made in conjunction with site investigation bedrock. is used for repository layout constructability forecast. The constructability forecast is included in total comparison material between sites, but is no direct safety-related importance. Good constructability is course advantageous. Coefficient No requirements No criteria during FS SI, but attention to rmal heterogeneous conditions. expansion Normal homogeneous properties preferable. Any problems with rock type boundaries are hled during detailed characterization repository construction. Future No requirements No grounds for comparisons or criteria in view loads uncertainties in forecasts. 72

69 6 Temperature 6.1 Thermal properties that influence function deep repository The rmal properties rock can above all influence isolating function deep repository. However, safety requirements can always be met by means a suitable layout repository. From construction viewpoint, but also indirectly from safety viewpoint, re is refore a preference that repository should not be too spread out. The necessary size repository area is influenced by rmal properties rock. Appendix A-3 summarizes how rmal properties influence functions what requirements preferences can be derived from this. The rmal evolution deep repository, as well as consequences this evolution for functions deep repository, are analyzed thoroughly in SR 97, Main Report, section 8.6 /SKB, 1999a/ Influence on canister integrity It is a requirement that maximum temperature on canister surface shall be lower than 100ºC /Werme, 1998/. It is not good if water boils so that salt deposits form which could later dissolve make groundwater more aggressive. (After closure, however, pressure, reby also boiling point, groundwater will increase considerably.) The temperature is determined by decay heat spent fuel, repository layout, rmal conductivity, heat capacity initial temperature rock, water saturation bentonite. The repository layout is determined so that temperature requirement is satisfied (see also Base Scenario in SR 97, Main Report /SKB, 1999a/). No requirements can refore be made on rmal properties rock. However, it is preferable that repository not be too spread out, since this leads to a more expensive repository could make site investigation more difficult increase risk that or undesirable properties in rock are not detected Influence on isolating retarding capacity buffer For same reasons as for canister, it is a requirement that highest temperature in buffer is lower than 100ºC. Higher temperatures in combination with unsuitable water chemistry could influence stability bentonite. However, this requirement is automatically satisfied if canister requirement is met. The possibility cannot be ruled out that an insulating air gap arises between canister bentonite /Bjurström, 1997/. The influence this gap was hled in /SKB, 1999a/ by assuming a temperature drop 10ºC between buffer canister, in addition a safety margin 10 degrees was assumed to manage uncertainties in various data /Ageskog Jansson, 1999/. The maximum permissible temperature at buffer s inner boundary was reby 80ºC. This requirement can always be met by means a suitable repository layout (see also 6.1.1). 73

70 6.1.3 Influence on isolating retarding capacity rock Thermomechanical requirements preferences regarding rock are discussed in chapter on rock mechanics, section 5.1. To guarantee isolating capacity rock, it is preferable that site should not have particularly suitable prospects for extraction storage geormal energy (competing interests). This question is discussed in General Siting Study 95, a preliminary conclusion is that this preference is satisfied by means suitability indicators already applied in feasibility studies. To simplify hydrogeological analysis, it is desirable that rmal convection not be a considerable driving force for groundwater flow, relative to or driving forces. As a rule, rmal driving force is negligible compared with topographical one (see e.g. Thunvik Braester, 1980). From a hydrogeological viewpoint, re are refore no reasons for requirement or preferences regarding rmal properties rock Biosphere-related matters The decay heat from repository must not cause a noticeable temperature increase at ground surface. Such an increase could affect ecosystems. However, analysis base scenario in SR 97 (Main Report, section /SKB, 1999a/) shows that heat from repository will only have an extremely marginal influence (equivalent to approximately 0.1% influence solar radiation) on rmal conditions on ground surface, so that this preference will always be satisfied Construction-related matters The layout deep repository is subject to an economic preference that each canister should hold as much fuel as possible. The layout must also satisfy above temperature requirements preferences. This is in principle always possible to do, but resultant temperature distribution for a given layout must be analyzed by rmal analysis in order to check temperature functions. Since re are also or factors (mainly occurrence regional local major fracture zones) that govern configuration repository, it is not certain that temperature requirements will ultimately determine extent repository. 6.2 Parameters that describe heat transport Description parameters ir influence on functions Heat transport through rock takes place primarily by heat conduction, which is determined by heat capacity rmal conductivity rock. (Heat transport by radiation convection can be neglected.) The heat transport through rock influences temperature in different barriers. Temperature changes also influence volume rock, which is determined by coefficient rmal expansion. This parameter has already been discussed in chapter on rock mechanics, section

71 It is a requirement that temperature on surface canister be less than 100ºC. If this requirement is met, temperature will not exceed 100ºC in any barriers eir. This requirement can always be satisfied by adjusting quantity fuel in canister or by adapting repository layout, for example by adjusting distance between deposition holes, provided rmal properties rock ambient temperatures (see below) are known. Good heat conduction high heat capacity are prerequisites for a more densely packed repository Requirements preferences There are no requirements regarding rmal properties rock, since applicable functional requirements can always be satisfied by a suitable repository layout. There is a preference for high rmal conductivity, i.e. λ>2.5 W(mK) 1 (Figure 6-1). At lower rmal conductivity, spacing between deposition holes in KBS-3 design must increase or amount fuel in each canister must decrease. It is also good if rock has homogeneous rmal properties. These preferences are mainly economical, since a more spread-out repository is more costly. Indirectly, however, preferences have some bearing on safety since it can be more difficult to characterize a very extensive complex repository area in a good way. The size repository area will, however, more probably be determined by existing fracture zones. As a rule, Swedish crystalline rock satisfies expressed preferences Generic knowledge knowledge obtained at different stages Typical value ranges for rmal properties crystalline bedrock in Fennoscian Shield have been compiled on basis a modified rock type grouping in accordance with Swedish National Atlas a statistical processing rmal properties based on mineral compositions according to Geological Survey Sweden /Sundberg, 1995 Sundberg, 1998/. Good correlations between values based on modal analysis (mineral composition) heat conduction measurement in field have been obtained in earlier studies /Ericsson, 1985 Sundberg, 1988/. Difference in mineral composition leads to different rmal conductivities in different rock types. Quartz has a rmal conductivity 7.7 W(mK) 1, which is 3 4 times higher than for or minerals. The quartz content a rock is refore crucial for its heat conduction. A simplified grouping mean values ranges for different rock types gives following results: Basic rock types (porphyrites, basic volcanites, dolerite, gabbro, diorite, amphibolite, etc.) have a mean value 2.5 W(mK) 1, values usually fall in interval W(mK) 1. Rock types intermediate composition (granodiorites, certain gneisses, certain volcanites) have a mean value 3.2 W(mK) 1 values usually fall in interval W(mK) 1. Quartz-rich rocks (granites, acid gneisses, quartzites, acid volcanites, etc.) have a mean value 3.6 W(mK) 1, with a typical value range W(mK) 1. The rmal properties are determined primarily on basis knowledge rock type composition. As mentioned previously (see section 4.4), knowledge main rock types in superficial bedrock is usually good during a feasibility study. Detailed knowledge rock type distribution is obtained during site investigations. 75

72 Figure 6-1. It is good if rock has a rmal conductivity higher than 2.5 W/(mK) Suitability indicators criteria Parameters for heat transport should be included as suitability indicators, since layout repository is in part determined by se parameters. The functional requirements can however always be met with ample safety by means a suitable repository layout. The parameters could be some importance for comparison between sites, since having a small repository area ( reby a small area that needs to be thoroughly investigated) can be economically advantageous. On or h, re are or factors (e.g. frequency fracture zones) that also influence size area that needs to be studied used. Moreover, deposition holes cannot be spaced too closely, for strength reasons among ors. It is refore no furr advantage if rmal conductivity is much higher than stated preference 2.5 W(mK) 1. During a feasibility study, knowledge exists which rock types exist in areas interest, an estimate can be made expected temperature at repository depth. This enables size repository as determined by heat considerations to be calculated. 76

73 In practice, however, heat parameters vary little within rock types such as granite gneiss, so that differences in se parameters will presumably be little importance for what areas are chosen for site investigation. It is only if rmal conductivity is judged to be less than preferred that size area that must be studied is affected. During site investigation, good knowledge exists rock composition heat conduction properties, which is used to adapt repository layout. However, rmal conductivity only influences size repository if re is a risk that it will be less than preferred. 6.3 Ambient temperatures Description parameters ir influence on functions The temperature distribution in rock is determined by transport parameters discussed in preceding sections by initial temperature rock groundwater (initial condition), which is chiefly determined by annual mean temperature on surface geormal gradient. Functional requirements preferences for temperature distribution can always be satisfied by adapting repository design layout (e.g. quantity fuel in canister, spacing between deposition holes or siting depth), provided rmal properties rock ambient temperatures are known. It is, however, an advantage if initial temperature at repository depth is not so great that it significantly affects spacing between deposition holes tunnels. Areas with large potential for geormal energy extraction (very high geormal gradient) should be avoided from a natural resource point view. However, such areas do not exist in Swedish bedrock Requirements preferences There are no requirements on ambient temperatures, except that areas with a large potential for geormal energy extraction (very high geormal gradient) should be avoided. In order to keep repository to a reasonable size, a preference is that initial temperature at repository depth should be less than 25ºC. However, this preference is only formulated from an economic perspective Generic knowledge knowledge obtained at different stages The initial temperature at 500 m depth lies between 7ºC (norrn Sweden) 18ºC (sourn Sweden). The rmal gradient lies between 10ºC/km 15ºC/km /Sundberg, 1995/. The initial temperature distribution in rock is determined primarily by geographic situation site, which means that good knowledge this can be obtained already during feasibility studies. Any anomalies can be revealed from boreholes in conjunction with site investigations. 77

74 6.3.4 Suitability indicators criteria The initial temperature at repository depth should be included as a suitability indicator, since design layout repository is partially determined by this parameter. The functional requirements can however always be met with ample safety by means a suitable repository layout. The initial temperature could be some importance for comparison between sites, however, since having a small repository area ( reby a small area that needs to be thoroughly investigated) can be economically advantageous. However, temperature is little importance for comparison between sites if it is judged to lie below preferred level (25ºC). There are or factors (e.g. strength, frequency fracture zones, etc.) that have a greater influence on how large an area needs to be studied used. Data for a more detailed repository layout are available during site investigation. 6.4 Summary suitability indicators temperature The preceding sections have provided an account which suitability indicators may be relevant in different stages siting work. The complete account work is found in Tables A-3 in Appendix A B-3 in Appendix B. As is evident from above, suitability indicators are mainly used to determine wher requirements preferences are satisfied. Table 6-1 provides a compilation suitability indicators that have been preliminarily identified for rmal properties. Table 6-1. Suitability indicators for rmal properties ( complete account is found in Appendices A B). Parameters Requirements or preferences Criteria during feasibility study (FS) groupwise during site investigation (SI) Heat transport No requirements FS: If an assessment is made (from rock conductivity (rmal types) that rmal conductivity is heat capacity) Preference regarding below preferred value, size area good rmal conductivity that must be studied is affected. (influences repository layout, repository size) i.e. SI: Detailed knowledge rock types λ>2.5 Wm 1 K 1. rmal conductivity is used to adapt repository layout. However, Thermal conductivity only has to be taken into account if re is a risk that it is below preferred level (2.5 Wm 1 K 1 ). Ambient temperature Areas with potential for FS: Avoid areas with assessed large (initial, external temper- geormal energy extrac- potential for geormal energy extraction. ature rmal tion (very high geormal If initial temperature is judged to exceed gradient). gradient) should be avoided. maximum preferred, it must be taken into Preference that initial temper- account in choice how large an area ature at repository level needs to be investigated. <25 C. SI: Like FS. The repository layout must take into consideration initial temperature if it is above or near maximum preferred. 78

75 7 Hydrogeology 7.1 Influence on function deep repository The groundwater flow through rock influences both isolating retarding functions deep repository. A review functions that are influenced by groundwater flow reveals that it is mainly permeability rock that influences functions, see Appendix A-4. Requirements preferences regarding parameters associated with hydrogeology are discussed in detail in following sections Influence on canister integrity To guarantee a suitable chemical environment for canister, groundwater unsuitable composition should not be able to flow to repository area for any extended period time. There is in principle a preference for low groundwater flow on a deposition hole scale in order to limit influx substances that could corrode copper canister, but calculations show (e.g. SR 97 base scenario /SKB 1999/) that flow does not play any significant role if sulphide content water lies within values that have been measured in deep groundwaters in Sweden Finl (see section 8.2.3). The canister s ability to withst hydrostatic pressures is site-independent. The canister is designed to withst, with a good margin safety, an external load composed hydrostatic pressure bentonite s swelling pressure /Werme, 1998/. The analysis in SR 97 furrmore shows that canisters can withst higher pressures that arise during a glaciation (SR 97, Main Report /SKB, 1999a/) Influence on isolating capacity buffer The groundwater flow in near zone influences wetting swelling buffer. Very uneven wetting can influence swelling pressure around canister during wetting process. The water content buffer also influences its rmal conductivity. After water saturation, an even swelling pressure arises. Maintenance water saturation swelling pressure are a prerequisite for buffer to act as a diffusion barrier. It is a requirement that swelling bentonite take place so that canister is not damaged. An uneven influx water to deposition hole may cause bentonite to swell unevenly, question has been raised wher this could pose a threat to canister. In previously performed simple hbook calculations /Werme, 1998/, a number hypotical cases uneven swelling were analyzed. The calculations did not take into account bentonite s inherent capacity to absorb deformations reby exaggerated importance uneven swelling. As a rule, however, se simple calculations show that resultant stresses are lower than strength canister. In some cases, though, more advanced calculations are needed to check wher re is a risk canister damage. FEM calculations were carried out within SR 97 where material properties bentonite were also taken into account to arrive at a more realistic load on canister /Börgesson Hernelind, 1998/. The largest tensile 79

76 stresses in canister insert were n found to lie below 55 MPa, which is far below yield strength cast iron insert. This means that re are no grounds for making requirements on even flows in deposition hole. There is a preference for a sufficient influx water from rock so that buffer is saturated quickly enough so that its rmal conductivity is sufficiently high. Function analyses swelling interaction with groundwater flow in rock were carried out in SR 97 (SR 97 Main Report, Chapter 8 /SKB, 1999a/ /Börgesson Hernelind, 1998/). The preference for low flows to achieve high retardation radionuclide transport (see section 7.1.3) is somewhat in conflict with preference for a sufficient influx water for swelling bentonite. The question is being studied in ongoing prototype repository project at Äspö HRL (see e.g. /Hermanson et al., 1999/). In unlikely event that problems should be encountered achieving sufficient water saturation in event excessively dry deposition holes, this can be solved by means various engineering measures. The preference for low flows to achieve good retardation is reby stronger than preference for a sufficient influx water for saturation bentonite Influence on retarding capacity geosphere It is preferable that transport radionuclides be retarded at buffer/rock tunnel/rock transition. Retardation is great at low groundwater flows few fractures with a small aperture where y intersect deposition holes /Moreno Gylling, 1998/. Calculations in SR 97 (Main Report, canister defect scenario /SKB, 1999a/) shows that if groundwater flow ( Darcy velocity ) for fractures that intersect deposition hole is greater than q max = 0.01 m/y, retardation at buffer/rock transition is virtually negligible (see section 9.2). Lower flows are course preferable, but re are no grounds for a requirement, since calculations also show that radionuclide release to biosphere can be kept below levels set in SSI s regulations /SSI, 1998/ even if retardation at buffer/rock transition is neglected. The groundwater flow between a damaged canister biosphere is an important factor for how much radionuclides are retarded in rock itself /Andersson et al., 1998b/. Calculations in SR 97 (Main Report, section 9.11 /SKB, 1999a/) show that retardation in geosphere is considerable for transport pathways that have a transport resistance (or F parameter) greater than 10 4 m/y (see section 9.3). Large transport resistances in geosphere are course preferable, but it is not possible to stipulate a more precise requirement than that overall barrier function should fer adequate safety. Radionuclide release to biosphere can be kept below levels set in SSI s regulations /SSI, 1998/ even if not all transport pathways from repository to biosphere have a high transport resistance Biosphere-related matters There are no requirements on near-surface conditions. From a natural resource viewpoint, it is preferable to avoid areas that are (or may be) important water sources, soil sources or farml. Thick, water-bearing soil strata complicate investigations from a constructional operational viewpoint. From a natural resource viewpoint, requirements/preferences exist to avoid areas where biological diversity or species worth protecting may be threatened directly or indirectly by construction access roads like in virgin areas. 80

77 Data on near-surface ecosystems are primarily valuable for building up a credible model description. In or words, good access to such data high quality increases credibility modelling reduces uncertainty results. Furrmore, impact on superficial groundwater (lowering groundwater table chemical changes) must be minimized. This entails preferences for limited seepage groundwater into repository during construction operation. This preference can be satisfied by means a suitable layout repository, choice grouting methods a suitable choice methods for building repository (see 7.1.5) Construction-related matters There are a number hydrogeological conditions that must be taken into account in configuration construction deep repository. A preference is that water seepage be moderate or that areas with too much seepage can be sealed with reasonable grouting measures (grouting need), since this affects costs building times. Grouting must be carried out so that re is no risk serious environmental impact or a negative impact on composition groundwater in deep repository. From an occupational safety viewpoint as well, probability heavy water seepage/cave-in must be low, but problems can always be managed with increased costs as a consequence. The repository is configured so that groundwater flow in repository area is low by avoiding regional local major fracture zones in deposition tunnels. 7.2 Permeability Description parameters ir influence on functions The magnitude groundwater flow its distribution in rock are primarily determined by permeability rock. The permeability a discrete fracture is oretically determined by its aperture. The aperture, reby permeability, fracture vary in its plane. The permeability a rock volume containing discrete fractures (e.g. a portion rock mass, a portion a fracture zone) is determined partly by permeability fractures in volume partly by how well y are connected with each or (connectivity). Rock without visible fractures has very low permeability. A larger rock volume contains thouss fractures, it is not possible to describe each fracture in detail. Instead, various macroscopic or statistical measures are used. The most common description is to represent permeability a rock volume a given size ( scale ) with its hydraulic conductivity (K). In small volumes (cubes a few tens metres or less on a side), hydraulic conductivity will vary widely in space. On a larger scale, spatial variation will decline (but mean value tends to increase slightly, see /Walker et al., 1997/). In groundwater model currently used by SKB, this spatial variation is described with a stochastic continuum model /Neuman, 1987; Norman, 1992/. 81

78 The permeability two-dimensional geometric objects (e.g. fractures fracture zones) can also be described by means a transmissivity distribution. The transmissivity (T) a fracture or a fracture zone is total hydraulic conductivity across entire aperture (width zone). Alternatively, permeability rock can be described with a stochastic discrete network model (Derschowitz et al., 1999/. The model is based on a statistical description orientation, size, frequency permeability discrete fractures. As a rule, permeability is described as a transmissivity distribution for discrete fractures. This model concept is studied as an alternative in SR 97. Compared with a continuum model, discrete model can provide more information on flow on a detailed scale on relationship between flow various conditions that influence radionuclide transport. It is complicated to discuss requirements preferences regarding permeability rock, since re are different models for describing permeability since properties are to some extent dependent on scale used for description. However, experience from extensive hydrogeological analyses carried out in SR 97 shows that it is meaningful to discuss preferences for permeability based on concept hydraulic conductivity on roughly a 30 m scale. The reasons are that radionuclide transport calculations have been based on results hydrogeological analyses on this scale that comparison between stochastic continuum model discrete network model show similar results. In future descriptions permeability rock, it is possible that SKB will choose or scales or or model concepts. The preferences given below can, however, be modified so that y could also be employed in se future descriptions Requirements preferences There are no direct requirements on transmissivity values for regional local major fracture zones. Such fracture zones are normally associated with large flows rapid transport pathways are refore not normally allowed to pass through individual deposition tunnels from a safety viewpoint (see section 4.6 Figure 7-1). Exceptions may be made from this requirement if it is possible to show that permeability fracture zone does not significantly deviate from that rest rock mass. If fracture zones are located outside repository area, ir permeability has a limited influence on safety. Theoretically speaking, it could even be an advantage if some se zones had high permeability, since this could shield f groundwater flow in repository area. For rock works it is preferable that fracture zones that have to be passed through during construction (i.e. normally local major local minor fracture zones) have such low permeability that seepage is moderate or that y can be sealed by normal grouting measures. Fracture zones with a low transmissivity (T<10 5 m 2 /s) do not constitute serious problems, but it is no serious obstacle if a few zones have higher transmissivity, provided y are not problematical from a construction viewpoint (e.g. high fracture density wearing, clay). A few more complex passages can be accepted. It is not possible to stipulate precise preferences for permeability individual local minor fracture zones from a safety point view. This is because it is geometric conditions properties in system fracture zones fractures that determine local groundwater flow capacity transport pathways through rock. However, it is generally speaking advantageous that frequency local minor fracture zones be low that y have low permeability. It is preferable that transmissivity does not exceed values used in SR 97 /Walker et al., 1997/. 82

79 Individual deposition holes may only be intersected by individual fractures. From a safety viewpoint it is preferable that aggregate permeability fractures that intersect deposition hole be small, since this causes retardation radionuclide transport in buffer/rock transition. However, radionuclide release from deep repository can be kept to very low values even if groundwater flow around deposition holes is very large. Calculations in SR 97 (/Walker Gylling, 1998/, /Walker Gylling, 1999/, /Gylling et al., 1999/, Data Report /Andersson, 1999/) show that Darcy velocity in near field will scarcely exceed q max = 0.01 m/y if hydraulic conductivity on 30 m scale is less than 10 8 m/s. In order to retain a contribution to retardation in buffer/rock transition, it is preferable to avoid areas where hydraulic conductivity on a deposition hole scale exceeds 10 8 m/s. The groundwater flow has a greater influence on how much radionuclide transport is retarded in rock between damaged canister biosphere. It is a clear advantage if groundwater flow is low, even though total release radionuclides ( resulting doses) is not mainly determined by retardation in rock. The Data Report s /Andersson, 1999/ compilation hydrogeological analyses (/Walker Gylling, 1998/, /Walker Gylling, 1999/, /Gylling et al., 1999/) shows that transport resistance rock is considerable (F greater than 10 4 m/y, see Chapter 9) if only a limited portion rock mass, on 30 m scale, has a hydraulic conductivity that exceeds 10 8 m/s 1) (Figure 7-1). Or factors (such as flow-wetted surface area, transport length hydraulic gradient) also exert an influence on size transport resistance (see Chapter 9), but if permeability lies within preferred range, transport resistance will be considerable when or factors have reasonable values. In or words, it turns out that relatively weak preference regarding hydraulic conductivity with a view towards influence on retardation in buffer/rock transition lies at same level as much stronger preference regarding influence on retardation in rock. In order for deposition to be practically possible, flow to individual deposition holes during deposition phase must not be too great. An upper limit has not yet been determined, but flow should in any case be less than 10 l/min. This preference can always be satisfied by means an active choice deposition holes ( possible sealing measures), but it is obvious that site will be less usable if rock contains few suitable canister positions. To keep inflow below 10 l/min, local conductivity around deposition holes (scale m) should preferably not exceed m/s. This means that construction-related safety-related preferences regarding permeability rock on a deposition hole scale are largely in agreement. In view complexity hydraulic information fact that groundwater flow is dependent on both permeability boundary conditions, it is always necessary to set up models for groundwater flow that can calculate function deep repository. This is true even if parameter values lie within preferable ranges. Finally, it should be pointed out that extensive research development efforts are still being conducted to be able to better describe groundwater flow transport in crystalline rock. This research development will probably show that above preferences can largely be satisfied by an active choice positions deposition holes in rock. 1) The value K<10 8 m/s can also be derived by means following simple approximations: F=a r L/q q=-kgrad(h) where a r is flow-wetted surface area per volume rock, L is transport pathway, q Darcy velocity, K hydraulic conductivity grad(h) gradient for groundwater head. If it is assumed that grad(h) is 1%, L is 30 m (may e.g. be distance to a major fracture zone) a r is approximately 1 m 2 /m 3, n F>10 4 y/m if K<10 8 m/s. 83

80 Figure 7-1. It is an advantage if a large portion rock mass in deposition area has a hydraulic conductivity (K) that is less than 10 8 m/s (on a scale 30 m). Fracture zones (regional local major ones) with large flows are normally not allowed to pass through individual deposition tunnels Generic knowledge knowledge obtained at different stages Value ranges for occurrence frequency fracture zones are discussed under heading Structural geology (see Chapter 4). On sites analyzed in SR 97 (data from Äspö, Finnsjön Gideå), hydraulic conductivity (30 m scale) fracture zones varied between m/s m/s. In a rock mass composed discrete fractures local minor fracture zones, hydraulic conductivity (30 m scale) varied between 10 6 m/s m/s. The values are based on an overall geostatistical analysis /Walker et al., 1997/. For municipalities investigated in feasibility study stage, well archive kept by SGU in compliance with Swedish law provides an approximate idea variation in permeability for uppermost 100 m in different rock types within municipality, see e.g. Folling et al. /1996/. A site investigation provides an opportunity to study variation in permeability at greater depth to determine (statistical) transmissivity distributions for individual fractures. The detailed characterization provides greater knowledge hydraulic properties fracture zones fractures that intersect or come close to investigation tunnels. 84

81 7.2.4 Suitability indicators criteria The permeabilities regional local major fracture zones are not essential suitability indicators, since se zones are avoided by adaptation repository layout. The geometric description se structures is, on or h, very important, see section 4.4. The permeability se zones is, however, still important to know in order to devise a good hydrogeological model site. The permeability portion rock that only contains local minor fracture zones discrete fractures should, however, be an important suitability indicator (see preferences regarding rock mass above). The uncertainties in estimate, as well as spatial distribution, must, however, be described hled, which complicates comparisons between sites. An overall hydrogeological modelling is necessary, even if simple approximate calculations can quickly provide a relatively good picture hydrogeological conditions that result from a given permeability. During feasibility study stage re is not enough information on hydraulic conductivity at depth to formulate useful criteria. A large fraction hydraulic conductivity values on a 30 m scale interpreted in site investigation for portion rock that is not located in interpreted fracture zones (rock mass) should be lower than 10 8 m/s. If this criterion is not satisfied, special requirements are made on careful adaptation repository to local conditions if safety margin is to be met. It is furr advantageous if repository is configured so that majority interpreted local major local minor fracture zones that need to be passed through by access tunnels have a transmissivity lower than 10 5 m 2 /s. If re are many zones with a higher transmissivity that are at same time wide clay-filled, this complicates configuration construction repository. Special attention must n also be given to possible environmental effects groundwater drawdowns grouting work. An assessment environmental impact construction work always needs to be done. 7.3 Porosity storage coefficients Description parameters ir influence on functions The flow porosity expresses relationship between volume permeable cavities fractures, total volume rock. The flow porosity influences transport rate non-sorbing substances, such as Cl, is refore an important parameter for transient modelling saltwater flow. However, flow porosity is less importance for retardation radionuclides that could occur in a release from a damaged canister (SR 97, Main Report, canister defect scenario /SKB, 1999a/). Most m have good sorption capacity, whereby retardation is completely dominated by matrix diffusion sorption, regardless very moderate retardation directly in permeable fractures. The few nuclides that do not have good sorption capacity have been able to leave canister buffer are so long-lived that ir residence time in rock is not enough to affect concentrations. 85

82 The storage coefficient is needed for transient evaluation pump tests. The storage coefficient is largely dependent on compressibility rock mass. It is little importance for function repository. For individual deposition holes, re is a requirement that porosity may not be so great that bentonite can be pressed out into large cavities n be eroded away. However, this requirement can easily be satisfied by active choice deposition holes does not lead to requirements on properties rock. For good near-field function (limited leakage radionuclides from buffer to surrounding rock) it is in principle favourable that porosity be as low as possible, but influence is weak re are no grounds for making requirements (see section 9.2) Requirements preferences There are no requirements on flow porosity or storage coefficient for any rock s structures or surrounding rock. Nor are re any special preferences for flow porosity. Values at repository depth should, however, not deviate greatly from normal conditions in Swedish bedrock (see next section), since experience is lacking from such (hypotical) conditions. However, if it should turn out that a site has very abnormal porosity conditions, this does not mean that site is unsuitable, just that furr research could be needed on importance porosity Generic knowledge knowledge obtained at different stages The flow porosity regional local fracture zones lies in range 10 3 < ε f < 10 2, while specific storage lies in range 10 6 m 1 < S s < 10 5 m 1. In rest rock, flow porosity lies in range 10 4 < ε f < 10 2, while specific storage is 10 7 m 1 < S s < 10 5 m 1. The values are based mainly on estimates made within Äspö project /Rhén (ed), 1992/, /Winberg (ed), 1996/, /Rhén (ed) 1997/. Flow porosity storage coefficient can be estimated in conjunction with site investigations Suitability indicators criteria The parameters are not useful as suitability indicators, since y are negligible importance for function deep repository, as explained above. No criteria need to be formulated. 7.4 Properties groundwater Description parameters ir influence on functions The density viscosity groundwater influence hydraulic conductivity. Furrmore, density variations (which may be due to both temperature concentration differences) give rise, via gravitation, to driving forces. The biggest temperature influence comes from repository, but this density influence is also relatively little 86

83 importance for groundwater flow /Thunvik Braester, 1980/. Density variations due to varying salinity can be more important need to be taken into account in groundwater calculations /Voss Andersson, 1993; Follin, 1995; Hartley et al., 1998/. In such calculations, however, it is necessary to take into account large-scale time-dependent changes, such as postglacial l uplift (crustal upwarping). High salinity at depth in bedrock may be an indication low groundwater flux, which in principle is favourable, but in case transient processes caused e.g. by l uplift, picture is not so simple saline water can also move. Saline groundwater also complicates hydrogeological characterization. Furrmore, a high salinity may be unsuitable for chemical reasons, since it may disturb various barrier functions (see Chapter 8). Saline groundwater, on or h, reduces risk that area will be used in future for abstraction groundwater for consumption Requirements preferences There are no requirements or preferences regarding density viscosity water from a hydrogeological viewpoint. However, it is important to be aware density conditions, y must be taken into account in groundwater modelling. From a hydrogeological viewpoint, it is not generally possible to say wher high salinities are an advantage or a disadvantage. From a chemical viewpoint, however, re is a clear requirement that total salinity at repository level may not be too high (see section 8.4) Generic knowledge knowledge obtained at different stages Groundwater density viscosity are influenced by prevailing temperature salinity. Salinity values are discussed in chemistry sections (section 8.4). Generic knowledge temperature distribution (see section 6.3) is sufficient to determine groundwater s temperature-dependent properties Suitability indicators criteria Groundwater density viscosity are not primary suitability indicators from a hydrogeological viewpoint. Salinity is an important indicator from a chemical viewpoint, however. However, high widely varying salinity conditions complicate analysis suitability a site. In any case, density variations must be taken into account in sitespecific hydrogeological modelling. This parameter is refore very important to know. The information available during feasibility studies does not permit meaningful sitespecific forecasts groundwater flow. If feasibility study indicates that re may be saline water at depth in investigated area (location in relation to coast, occurrence saline groundwater in rock-drilled wells, etc.), this probably means that hydrogeological situation needs to be described in part as transient density-dependent flow. This should influence which data are gared during site investigation. If site investigation shows that groundwater down to about m has higher salinities than about 1%, it is necessary to at least partially model groundwater flow as transient density-dependent /Freeze Cherry, 1979/. 87

84 7.5 Near-surface ecosystems Description parameters ir influence on functions The near-surface ecosystems can be described in terms identified ecosystems (forest, lake, meadow, etc.), ir activity (l use, uptake rates, etc.) transport water particles (meteorological/hydrological data) as well as hydrogeological description (permeability, thickness porosity) soil strata. The information is needed to be able to describe turnover, transport pathways consequences radionuclides that escape into environment. The near-surface conditions also influence groundwater recharge groundwater chemistry, even though groundwater flux at depth is very slow Requirements preferences There are no requirements on near-surface conditions. The repository s isolating retarding function should in any case be so good that adequate safety can be achieved regardless what ground recipient conditions prevail. Areas protected by law shall be avoided. From a natural resource viewpoint re is a preference to avoid areas that are (or may be) important water sources, soil sources or farml. Thick, water-bearing soil strata complicate investigations. From a natural resource viewpoint, it is preferable when building surface facility to avoid areas where biological diversity or species worth protecting may be threatened directly or indirectly by construction access roads like in virgin areas. Data on near-surface ecosystems are primarily valuable for building up a credible model description. In or words, good access to such data high quality increases credibility modelling Generic knowledge knowledge obtained at different stages Specific runf in Sweden varies in round figures between mm/y. The hydraulic conductivity soil strata lies in range 10 9 m/s to 1 m/s. Normal soil depths lie in range 0 30 m. Only in exceptional cases have depths up around 100 m been measured in Sweden. The site-specific near-surface information on recipient conditions hydrogeology can be obtained without conducting a drilling programme. Some information is obtained in conjunction with feasibility studies. But existing data may need to be compiled furr. Moreover, additional more detailed information needs to be collected during site investigations preparations for m Suitability indicators criteria Conditions in near-surface ecosystems do not constitute geoscientific suitability indicators, but are course taken into account in siting a repository. Areas with high values from a nature conservation or natural resource viewpoint are identified during feasibility studies. If a site investigation is planned in such an area, it is a requirement that special consideration be given to se values. 88

85 A preliminary adaptation surface portions deep repository to nearsurface ecosystems is first done based on information obtained from feasibility study. Areas protected by law are avoided. It is a preference that areas interest for site investigations have few competing interests that surface facility can be preliminarily adapted so that re is little impact on near-surface ecosystem. A more detailed analysis adaptation are performed at an early stage during site investigation in connection with choice area for continued site investigation, but same basic criteria are applied. 7.6 Boundary conditions supporting data Description parameters ir influence on functions There are several different hydrogeological data that pertain to aspects groundwater flow but are not included as independent model parameters in hydrogeological modelling. These include pore pressure, groundwater s hydraulic head ( sum pressure head elevation head groundwater table ), measured groundwater flow, characterization recharge discharge areas, results large-scale pumping tracer tests. Such data can be used to check reasonableness models (supporting data) or for setting boundary conditions. Specific factors to take into account are: i) hydraulic gradient, ii) distribution recharge discharge areas, iii) shoreline displacement due to l uplift etc. The pore pressure directly influences canister function (see 7.1.1). Stipulated requirements are met by not making repository too deep, since pore pressure is determined by depth (with very small variations). The gradient for groundwater s hydraulic head is most important driving force for groundwater flow. In principle, lower gradient, lower groundwater flow. On a large scale, gradient does not vary as much as permeability rock, but is determined to a high degree by topographical variation. Counted over large areas, hydraulic gradient cannot be greater than topographical gradient, but it can be lower than topographical gradient in areas with high permeability. This means that areas with a locally small hydraulic gradient do not always have to have a low groundwater flow. If permeability is very high, groundwater recharge will not suffice to keep groundwater s hydraulic head at ground surface gradient may be very low, even if groundwater flow is high. Outside Caledonian mountain range, regional topographical gradient in Sweden is limited generally lower than 1% (see section 4.2.3). Variations hydraulic gradient within such relatively flat areas are only partially linked to where groundwater flow is great. It is primarily permeability rock that determines size groundwater flow. At high salinities, where density differences can give rise to flow forces which also drive groundwater flow, situation is complicated by fact that driving force can no longer be described solely as a gradient a hydraulic head distribution. However, this does not appreciably influence above argument. The distribution recharge discharge areas provides important information for setting boundary conditions for hydrogeological models, even though groundwater flux at depth is mainly determined by permeability deep rock. In principle, it should be an advantage to locate repository beneath a recharge area, since this should maximize length flow paths from repository. However, groundwater that passes repository will eventually come up in a discharge area, 89

86 present-day groundwater models indicate that se discharge areas are ten situated not far from repository (/Walker Gylling, 1998/, /Walker Gylling, 1999/, /Gylling et al., 1999/), since circulation is controlled to a high degree by structures in rock local topography. The distribution recharge discharge areas is taken into account in part safety assessment that describes effects near-surface ecosystems. The near-surface ecosystems are also good indicators potential recharge discharge areas. Shoreline displacement alters boundary conditions for all sites situated in near-coast areas. A future glaciation will have a far-reaching impact on groundwater flow, regardless location site. The effects se two processes are discussed analyzed within framework climate scenario in SR 97 Main Report /SKB, 1999a/ Requirements preferences Generally, boundary conditions supporting data are primarily valuable in building up a credible system description. In or words, good access to such data high quality increases credibility modelling. There are no requirements regarding hydraulic gradients, distribution recharge discharge areas or shoreline displacement. There is a preference that natural local hydraulic gradients at repository level are not higher than is normal outside Caledonian mountain range (i.e. lower than about 1%). Very low hydraulic gradients are no furr advantage, however. It is in principle advantageous if repository area is located beneath a local recharge area, but in view fact that discharge areas are ten situated not far from repository (see above), it is doubtful wher this preference should be given particularly great weight. Adequate safety retention capacity must in any case be demonstrated in site-specific safety assessment. If shoreline displacement is considerable it is necessary to take this into account in hydrogeological modelling, since assumptions steady states can lead to a misconception regarding groundwater flow /Voss Andersson, 1993; Svensson, 1999/. Modelling is simplified if shoreline displacement is small, but rate l uplift in Sweden is so great that shoreline displacement must be taken into account everywhere along Swedish coast north Skåne (Scania). There are no grounds for making requirements or preferences regarding glaciation frequency. Glaciation is analyzed as a scenario in safety assessment Generic knowledge knowledge obtained at different stages Typical values in SR 97 for natural regional gradient at repository depth are % for Äspö, % for Finnsjön % for Gideå /Walker et al., 1997/. Regarding forecasts shoreline displacement future glaciations, reference is made to climate scenario in SR 97 Main Report, Chapters 6 10 /SKB, 1999a/. Information on recharge discharge areas, as well as notions gradients (based on topography), are probably known already from feasibility studies. Additional, more detailed information can be gared during site investigations. Measurements pore pressures hydraulic heads can only be obtained in site investigations. Forecasts shoreline displacement glaciations are not influenced by different phases in a site investigation. 90

87 7.6.4 Suitability indicators criteria Supporting data are not primarily useful as suitability indicators, but rar are needed to build up credible system descriptions. Difficult-to-interpret data, or difficulty in achieving agreement between models supporting data, should however be negative from a siting viewpoint. Only Caledonian mountain range is clearly unsuitable due to high gradients, but it has already been excluded for or reasons (see General Siting Study 95 /SKB, 1995b/). Particulars on hydraulic gradient, as well as distribution discharge recharge areas, are essential for hydrogeological understing site, but vary too little to be primary suitability indicators. Forecasts glaciation frequency are not useful suitability indicators. Firstly, re are no special grounds for making requirements or preferences. Secondly, such forecasts must be regarded as far too uncertain to serve as a basis for site selection. The glaciation scenario is analyzed in safety assessment, regardless which site will be chosen. Particulars on topographical gradient shoreline displacement are obtained during feasibility study. Areas with unsuitably high topographic gradients (much greater than 1%) are screened out already during feasibility studies. During site investigation associated hydrogeological modelling, it should be possible to assess situation for recharge discharge areas that are linked to groundwater flow that passes through repository. The information is used in site-specific safety assessment. Good safety isolating capacity can, however, also be obtained if repository is located near a recharge area. It is refore not warranted to formulate criteria in advance based on distribution recharge discharge areas. All supporting data are taken into account in hydrogeological modelling that is carried out during site investigation. 7.7 Summary suitability indicators hydrogeology The preceding sections have provided an account which hydrogeological suitability indicators may be relevant in different stages siting work. The complete account work is found in Table A-4 in Appendix A Table B-4 in Appendix B. As is evident above, suitability indicators are mainly used to assess wher requirements preferences are satisfied. Table 7-1 provides a compilation suitability indicators that have been preliminarily identified for hydrogeology. 91

88 Table 7-1. Suitability indicators for hydrogeology ( complete account is found in Appendices A B). Parameters Requirements or preferences Criteria during feasibility study (FS) groupwise during site investigation (SI) Permeability for Deposition holes are not allowed For adaptation to geometry fracture fracture zones to be positioned near regional or zones fractures see geology. fractures local major fracture zones. (Exceptions may be made from this requirement FS: No criteria. if it can be shown that permeability does not deviate from rest SI: A large fraction interpreted K values rock mass.) See furr fracture in rock mass are K<10 8 m/s. (Orzones geology. wise need for local detailed adaptation if safety margin is to be met.) It is an advantage if a large portion rock mass in deposition Fracture zones that need to be passed area has K<10 8 m/s (on deposition during construction should have an interhole scale). Integrated function preted transmissivity T< 10 5 m 2 /s analysis is needed. lack clay filling (orwise increased attention to grouting or construction- Zones that need to be passed during related risks). construction should have such low permeability that passage can take place without problems. (Zones with T<10 5 m 2 /s or zones that are not difficult from a construction point view.) Flow porosity No, since parameters do not storage coefficient influence retardation sorbing substances or long-lived non-sorbing substances (see transport). Density viscosity Density differences influence hydrogeological modelling, but are not grounds for requirements/ preferences (see however chemistry). Near-surface Areas protected by law are avoided. FS: Areas protected by law shall be ecosystems avoided. It is a preference that areas Avoid areas for deep repository s interest for site investigations have surface facilities where biological few competing interests that diversity organisms worth protec- surface facilities can be preliminarily ting may be threatened areas that adapted so that re is little impact are or may be important water sour- on near-surface ecosystem. ces, soil sources or farml. Data on near-surface ecosystems are SI: Criteria as above. primarily valuable for building up a credible model description. Supporting data Data are primarily needed to FS: Areas with an unsuitably high gradient (hydraulic heads, build up credible groundwater (much greater than 1%) are screened out. recharge dis- models. charge areas, etc.) SI: Information on supporting data are Advantage if local gradient <1% primarily used to build up credible at repository level (but no furr models. advantage if even lower). 92

89 8 Chemistry groundwater composition 8.1 Influence on function deep repository The composition groundwater influences both isolating retarding functions deep repository. A review functions that are influenced by composition groundwater reveals that functions are influenced by a few essential hydrogeochemical parameters, see Appendix A-5. Requirements preferences regarding se hydrogeochemical parameters are discussed in detail in following sections in this chapter Influence on canister integrity It is a requirement that composition groundwater at canister be such that general corrosion copper cannot occur (that copper is rmodynamically stable). This means that no dissolved oxygen may be present in groundwater around canister for any extended period time. It is furr preferable to have a low total salinity low concentrations substances that influence corrosion such as sulphide, ammonium, nitrite nitrate. Copper corrosion is discussed in Base Scenario for SR 97 /SKB, 1999a/ based on studies by /Werme et al., 1992; Wersin et al., 1994/ as well as different reports produced by Posiva in Finl /Ahonen, 1999; Saario et al., 1999/ Influence on release to groundwater A groundwater composition that retards fuel dissolution leads to low solubility released nuclides is preferable. The model for fuel dissolution that is used in canister defect scenario in SR 97 (Main Report /SKB, 1999a/) assumes that surrounding groundwater is free from dissolved oxygen. To simplify analysis, requirement oxygen-free conditions also ensures slow fuel dissolution. But process fuel dissolution is controlled in model by oxidants that are formed by radiolysis water that comes into contact with fuel. Even if fuel is dissolved, constituent substances can be re-precipitated, whereby resulting leaching-out process is controlled by solubility substances. The uncertainties in calculated solubilities are discussed with regard to input data in Bruno et al. /1997/. Solubility is above all influenced by redox conditions, ph, carbonate concentration temperature. Preferences regarding composition are set based on fact that solubilities shall not be appreciably higher than what is used in SR 97 safety assessment /SKB, 1999a/. 93

90 8.1.3 Influence on stability buffer Groundwater composition influences bentonite stability, which in turn influences buffer s isolating retarding capacity. It is a requirement that buffer s swelling pressure be preserved (Main Report SR 97 /SKB, 1999a/). If pore water in bentonite contains salt, which may be a consequence eir fact that bentonite has been saturated with saline groundwater or that salt has diffused into pore water after saturation, swelling pressure swelling capacity are influenced /Karnl, 1997/. Swelling pressure decreases with increasing salinity. The decrease is greatest in relative terms at a low degree bentonite compaction. In order for clay gel to be chemically stable not be dispersed to a colloidal suspension, it is furr necessary that water contain a sufficient concentration positive ions (SR 97, Main Report, section /SKB, 1999a/). The clay gel is stable if concentration divalent ions (calcium magnesium) exceeds 4 mg/l /Laaksoharju et al., 1995/ Influence on retardation in geosphere The composition groundwater influences several rock s retention properties particularly sorption (see e.g. /Carbol Engkvist, 1997/) diffusion into rock matrix. There is a risk that retention will be degraded if water contains colloids. There is a general preference for good sorption properties in rock, little organic complexation negligible colloid transport. There are no absolute requirements, but overall geosphere function shall be sufficient to provide adequate safety in an integrated safety assessment. It is above all groundwater s total salinity, ph, Eh carbonate that influence retention properties Biosphere-related matters Knowledge composition near-surface groundwater is needed to describe near-surface ecosystems. This knowledge is also important to show wher more recently discovered changes are caused by repository or are a consequence natural evolution conditions Construction-related matters There are a number chemical conditions that must be taken into account in connection with configuration construction deep repository. Concentrations substances that are dangerous from an occupational health viewpoint (e.g. radon) must be kept below limit values. (This can as a rule always be achieved by e.g. good ventilation.) The composition water (Cl, SO 4 2, CO 2 ) can influence choice suitable grouting agents. But re are no grounds for requirements or preferences. Limited environmental impact investigations (e.g. necessitating diversion saline groundwater) construction operation (e.g. influence blasting gases or grouting) is a requirement. 94

91 8.2 Indications occurrence dissolved oxygen Description parameters ir influence on functions There is overwhelming evidence from analyses groundwater in crystalline rock that groundwater does not contain dissolved oxygen at repository level. Investigations have been conducted in Sweden, Finl Canada, see e.g. /Laaksoharju et al., 1993, Laaksoharju et al., 1998/. If re were dissolved oxygen in groundwater, this could lead to corrosion copper canister. Sulphide in groundwater can also attack copper canister, see section However, oxygen is much more problematical than sulphide, since oxygen can cause pitting. Indication that dissolved oxygen does not occur is refor essential in fulfilling fundamental safety function an intact canister. Occurrence oxygen also influences fuel dissolution, solubilities sorption properties in buffer rock (see 8.1). For se functions as well, absence dissolved oxygen is advantageous. There are several different chemical parameters that can be used as indicators to see if re is any dissolved oxygen in groundwater. Presence dissolved oxygen in groundwater is indicated by measurements redox potential (Eh). If dissolved oxygen is present, measured values are positive. If no dissolved oxygen is present, which is case in deep groundwaters, redox potential is determined by iron II/III ratio, or by sulphide or sulphur compounds in water. Then values are normally negative. The Eh is measured continuously during hydrogeochemical borehole investigations provides a good idea conditions already during actual investigation campaign. In some cases it can be difficult to obtain reliable Eh values, such as under difficult sampling conditions /or if concentrations iron sulphide are low. Then occurrence Fe 2+, Mn 2+ or HS is in itself pro absence dissolved oxygen. These substances are analyzed on samples taken during investigation campaign Requirements preferences It is a requirement for canister isolation that, under undisturbed conditions shortly after repository has been closed, no dissolved oxygen should occur at repository depth (see Figure 8-1). In order for this requirement to be satisfied, at least one indicators negative Eh, occurrence Fe 2+ or occurrence HS must be satisfied, or it must orwise be possible to prove that dissolved oxygen does not occur Generic knowledge knowledge obtained at different stages Measurement data from deep groundwaters in Sweden Finl /Laaksoharju et al., 1993, Laaksoharju et al., 1998/ show that above requirement is always met. At repository depth, Eh values are negative, concentrations F 2+ lie in range 5 µg/l 10 mg/l, sulphide concentrations lie in range mg/l. General siting studies or feasibility studies do not contribute any new knowledge about aforementioned oxygen indicators compared with general knowledge that already exists. The essential site-specific information on parameters is obtained in water samples from deep boreholes that are drilled in conjunction with site investigations. Detailed characterization (investigations from tunnels) may contribute new knowledge in portion rock that has very low permeability. 95

92 Figure 8-1. Dissolved oxygen must not occur at repository depth. Oxygen dissolved in surface water is normally consumed in soil zone, but may reach greater depth in fracture zones Suitability indicators criteria It is obvious that parameters that can indicate presence dissolved oxygen are very important suitability indicators, since y are linked to requirements. Furrmore, parameters can be successfully determined in a site investigation. No meaningful criteria can be set up before site investigations are completed. However, experience shows that above requirement can be expected to be satisfied. During site investigation, at least one indicators negative EH values, occurrence Fe 2+ or occurrence HS must be satisfied. If none indicators can clearly demonstrate absence dissolved oxygen, a deeper chemical assessment is required. Studies Fe(II) sulphide minerals, such as pyrite biotite, can be used to furr clarify redox conditions. If not even se furr studies are able to demonstrate oxygen-free conditions, site must be aboned. 96

93 8.3 ph Description parameter its influence on functions Extensive experience data are available on ph conditions in crystalline rock. ph is controlled for most part by calcite/carbonate system. The ph groundwater primarily influences canister corrosion, sorption (/Carbol Engkvist, 1997/, /Yu Neretnieks, 1997/) solubilities radionuclides /Bruno et al., 1997/ (see also SR 97 SR 97 Main Report Chapter 8 /SKB, 1999a/) Requirements preferences It is a preference that ph groundwater below 100 m lie between All ph values within this range are in principle equally suitable. There are no preferences for groundwater above a depth 100 m. The preference is based above all on fact that knowledge base for sorption parameters ( K d values ) used in safety assessment derives from measurements within preferred ph range. If values lie outside range, database needs to be augmented Generic knowledge knowledge obtained at different stages Measurement data from deep groundwaters in Sweden Finl show that ph below a depth 100 m is between 6 10 as a rule, but deviations (higher values) occur, for example at Stripa /Laaksoharju et al., 1993 Laaksoharju et al., 1998/. Lower ph values occur above 100 m. Different general siting studies or feasibility studies do not contribute any new knowledge about ph compared with general knowledge that already exists. The essential site-specific information on parameters is obtained in water samples from deep boreholes that are drilled in conjunction with site investigations. Detailed characterization (investigations from tunnels) may contribute new knowledge about ph in low-permeable rock Suitability indicators criteria ph is a useful suitability indicator since it is linked to preferences. The parameter can also be successfully determined in a site investigation. No meaningful criteria can be set up during feasibility studies. However, experience shows that above preferences can be expected to be satisfied. In site investigations, quality-approved measured ph values should lie within stipulated preference interval (6<pH<10) below 100 m level. If this criterion is not satisfied, a deeper analysis, augmentation database for sorption parameters possibly extended sampling are needed. If analysis shows that ph deviates significantly from stipulated ranges, suitability site may be questioned. 97

94 8.4 Total Dissolved Solids (TDS) Description parameters ir influence on functions Total salinity (TDS = Total Dissolved Solids ) mainly influences bentonite s stability sorption radionuclides. If TDS is very high, bentonite s swelling capacity decreases (Karnl /1997/), at concentrations higher than 100 g/l buffer s swelling capacity may have declined by more than half for a bentonite with a density 2,000 kg/m 3. High salinities also reduce sorption capacity in rock many radionuclides (Carbol Engkvist /1997/). Very high salinities (TDS>200 g/l) in combination with very low ph (ph<3) also influence stability copper (SR 97 Main Report section 8.9 /SKB, 1999a/). However, such low phs cannot occur at repository depth due to reaction between minerals water /Stumm Morgan, 1996/ Requirements preferences It is a requirement that TDS <100 g/l in deposition area (Figure 8-2). Thorough investigations are required to clarify wher bentonite can withst higher concentrations with undiminished swelling capacity. Figure 8-2. Total salinity must be less than 100 g/l in deposition area. 98

95 8.4.3 Generic knowledge knowledge obtained at different stages Measurement data from deep groundwaters in Sweden show that down to a depth 1,000 m, TDS lies within interval 0 35 g/l. Even higher concentrations occur at greater depths. Concentrations up to 100 g/l have been measured at a depth 1,700 m /Laaksoharju et al., 1993, Laaksoharju et al., 1998/. The depth to groundwater with high salinities is as a rule greater inl than on coast. In Finl, a TDS 70 g/l has been measured at depths below 800 m /Pitkänen et al., 1998/. Different general siting studies or feasibility studies do not contribute any new knowledge on TDS or content essential ions compared with general knowledge that already exists. The essential site-specific information on parameters is obtained in samples/measurements from deep boreholes that are drilled in conjunction with site investigations. Detailed characterization may contribute new knowledge on TDS in portion rock that has very low permeability Suitability indicators criteria TDS at repository level is a useful suitability indicator. No meaningful criteria can be set up before site investigations are completed. However, experience shows that elevated TDS can be expected in locations relatively near coast in relatively flat terrain. In site investigations, all quality-approved TDS values measured at planned repository depth shall meet above requirement. Occasional higher values can be accepted if it can be shown that water is located in areas that can be avoided that water will not flow to repository area. 8.5 Organic substances or components in groundwater Description parameters ir influence on functions DOC sts for Dissolved Organic Carbon designates quantity dissolved organic carbon measured in groundwater. DOC is reby a measure quantity organic matter measured as total organic carbon in solution. The amount organic matter in water influences e.g. bacterial transformation sulphate to sulphide (SR 97 Process Report section /SKB, 1999b/, /Pedersen Karlsson, 1995/). The sulphide concentrations in Swedish groundwaters are generally limited by fact that sulphide precipitates as solid minerals when sulphide concentrations become sufficiently high. The solid minerals are formed above all by reaction with iron. Furrmore, buffer limits transport sulphide up to canister. Calculations show that it would take longer than 10 million years to corrode a copper canister 1 cm, even if concentration sulphide were around 1 mg/l /SKB, 1999b/. High concentrations nitrogen phosphorus compounds are undesirable since y stimulate bacterial growth. High concentrations nitrogen compounds can cause stress corrosion cracking in copper /Benjamin et al., 1988; SR 97 Process Report 3.7.6, SKB, 1999b; Saario et al., 1999/. 99

96 It is necessary to know quantities types nutrients that remain in rock when repository is closed. If se quantities are acceptable at closure, re are no processes in rock which can in long run lead to an increase to an unacceptable level. The stability bentonite is influenced by concentrations Na +, Ca + Mg +. Low concentrations can reduce stability bentonite gel, from which colloidal particles can n be carried away by groundwater /Laaksoharju et al., 1995/. The occurrence colloids, humic fulvic acids, free gas (as H 2, N 2, CH 4, CO 2, He Ar) bacteria influence conditions for radionuclide transport. For example, sorbing radionuclides can be transported with water if y adhere to colloidal particles in groundwater. However, transport process is completely negligible at colloid concentrations that normally occur in deep groundwaters /SKB, 1999a; Allard et al., 1991/. In a similar manner, gas bubbles bacteria can be carriers radionuclides. Complexation with humic fulvic acids can reduce sorption some radionuclides. The concentrations Ra Rn influence what occupational safety measures are needed during repository construction. These concentrations are linked to concentration U Th in bedrock can thus be estimated based on knowledge rock type (see 4.4). A large number or components in water are also measured during analysis groundwater composition. This is needed for a proper chemical understing, but no or components are directly linked to requirements or preferences Requirements preferences There are no grounds for requirements regarding organic substances or or components in groundwater. Near-surface waters (0 100 m) should contain more than 10 mg/l DOC to ensure reduction dissolved oxygen in infiltrating groundwater /Banwart (ed) 1995/. Lower concentrations are desirable at repository depth, lower better. Low values ammonium (NH 4+ ) are preferable, but how low values are desirable is still subject investigation. It is an advantage if concentrations [Ca 2+ ]+[Mg 2+ ] > 4 mg/l at repository depth (SR 97 Main Report, section /SKB, 1999a/, /Laaksoharju et al., 1995/). Higher values are no furr advantage, however. Low concentrations colloids (<0.5 mg/l) absence free gas (bubbles) at repository level are preferable, since se parameters can influence transport radionuclides in geosphere. The occurrence dissolved H 2 or CH 4, on or h, indicates reducing conditions is advantageous from viewpoint deep repository. Low concentrations Ra Rn are preferable for working environment, but suitable protective measures (ventilation) can always be adopted if levels are too high. 100

97 8.5.3 Generic knowledge knowledge obtained at different stages Measurement data from deep groundwaters in Sweden Finl show that at planned repository depth, DOC is as a rule less than 10 mg/l. Considerably higher concentrations can occur during just after construction phase, but y will quickly come down to lower levels as organic matter reacts with entrapped oxygen /Puigdomenech et al., 1999/. The highest sulphide concentrations that have been measured in Swedish groundwaters lie around 1 mg/l. Sulphide concentrations 5 10 mg/l have been measured in rock volumes beneath sea sediment, where extensive sulphate reduction occurs. Measurement data from deep groundwaters in Sweden Finl show that at planned repository depth, concentrations [Ca 2+ ] [Mg 2+ ] lie within preferred ranges. [Ca] lies in interval 21 1,890 mg/l [Mg] in interval mg/l /Laaksoharju et al., 1993, Laaksoharju et al., 1998/. The median concentration colloids in groundwater at planned repository depth is less than 0.05 mg/l /Laaksoharju et al., 1995/. Considerably higher concentrations can occur during construction phase. Different general siting studies or feasibility studies do not contribute any new knowledge on DOC or or chemical parameters at repository depth. The essential site-specific information on parameters is obtained in water samples from deep boreholes that are drilled in conjunction with site investigations. Detailed characterization contributes new knowledge about conditions in low-permeable rock at repository level, but re is a risk temporary disturbances during construction period due to mixing processes Suitability indicators criteria None above preferences are sufficiently important to constitute grounds for suitability indicators. The concentrations are essential to know, since y comprise important information concerning chemical hydrogeological evolution site. Good knowledge se conditions leads to better understing, reby reducing non-quantifiable uncertainty regarding properties future evolution site. It is not possible to formulate criteria for or parameters solely on basis knowledge that exists during a feasibility study. Special attention investigations may, however, be necessary if concentrations measured during a site investigation deviate from preferred. 8.6 Summary suitability indicators chemistry Table 8-1 provides a compilation suitability indicators that have been preliminarily identified for hydrogeochemical composition. The complete account work is found in Tables A-5 in Appendix A B-5 in Appendix B. 101

98 Table 8-1. Suitability indicators for hydrogeochemical composition. (The complete account is found in Appendices A B). Parameters Requirements or preferences Criteria during feasibility study (FS) groupwise during site investigation (SI) Dissolved oxygen Requirement: Absence dis- FS: No criteria (no data available) but solved oxygen at repository re is no reason to believe that level (indicated by negative Eh, requirement cannot be met. occurrence Fe(II) or occurrence sulphide). SI: At least one indicators Eh, Fe 2+, HS must be satisfied. ph Preference: Undisturbed ground- FS: No criteria (no coupling to surface water at repository level should water). have a ph in range SI: below 100 m level, quality-approved values should lie in range Total dissolved Requirement: TDS<100 g/l FS: No criteria solids (TDS) SI: Quality-approved measured TDS at repository level must meet this requirement. Occasional higher values can be accepted if it can be shown that water is located in areas that can be avoided. Or chemical Preference: [DOC]<20 mg/l, FS: parameters colloid concentrations <0.5 mg/l, low ammonium concentrations SI: Attention to wher measured [Ca 2+ ]+[Mg 2+ ]>4 mg/l at repository concentrations deviate from preferences. depth, low concentrations Rn, Ra. 102

99 9 Transport properties rock 9.1 Influence on function deep repository The retarding function deep repository is dependent to a large extent on transport properties rock, but transport properties also have some influence on isolating function deep repository. Appendix A-6 summarizes how transport properties rock influence se functions. The transport processes in rock, primarily radionuclide transport, are thoroughly analyzed in SR 97 (Main Report, Chapter 9 /SKB, 1999a/) Influence on integrity canister buffer To guarantee a suitable chemical environment for canister buffer, groundwater unsuitable composition should not be able to flow to repository area for any extended period time. The stable chemical environment in rock (see Chapter 8) shows that no specific requirements need to be made on rock in this respect, however Influence on retarding capacity geosphere The importance some retardation is dependent to a high degree on how great retardation is in relation to half-lives various radionuclides. In general, retardation can reduce release relatively short-lived nuclides by giving m time to decay, while relatively long-lived nuclides may remain more or less unaffected. The magnitude retardation can vary greatly between different nuclides (different sorption properties) between different conditions in rock. The size groundwater flow is ten crucial importance. The transition between buffer rock can entail a considerable retardation released radionuclides. The retardation in transition is dependent on groundwater composition (or Darcy velocity) on a deposition hole scale geometry fractures that intersect deposition hole /Moreno Gylling, 1998/. Calculations in SR 97 (Main Report, section 9.11 /SKB, 1999a/) show that buffer/rock transition is importance in retarding several nuclides, conditions leading to high retardation are naturally preferable. There are, on or h, no grounds for requirements, since calculations also show that release to biosphere can be kept below levels set in SSI s regulations /SSI, 1998/, even if retardation in transition is neglected. The retardation in rock itself ( geosphere) is determined mainly by transport resistance ( F parameter ) in geosphere, which is dependent on groundwater flow, flow paths flow-wetted surface area (see e.g. /Andersson et al., 1998b/), by diffusivity porosity rock matrix by capacity radionuclides to sorb on rock matrix. The sorption capacity different substances is determined to a large extent by ir speciation, which is in turn dependent on composition groundwater. Consequence calculations in SR 97 (SKB, 1999, Main Report, section 9.11 /SKB, 1999a/) demonstrate that transport resistance has a very great influence on 103

100 retardation. The transport resistance also influences breakthrough time for nuclides with little sorption, but very long-lasting releases nuclides with a long half-life negligible sorption are not affected at all by retardation in rock. Large transport resistances in geosphere are course preferable, but it is not possible to stipulate a more precise requirement than that aggregate barrier function shall suffice to ensure adequate safety. The release to biosphere can be kept below levels set in SSI s regulations /SSI, 1998/, even if not all transport pathways from repository to biosphere have a large transport resistance. 9.2 Flow parameters on deposition hole scale Description parameters ir influence on functions In a repository KBS-3 type, groundwater flow fracture aperture influence retardation radionuclides between buffer rock /Moreno Gylling, 1998/. The influence is relatively limited, however, calculations carried out within framework SR 97 (Main Report, section 9.11 /SKB, 1999a/) show that at higher values groundwater s Darcy velocity than approximately 0.01 m/y, retardation is no longer dependent on groundwater flow. The importance retardation in buffer/rock transition is furr dependent on which nuclides are being considered (see 9.1.2) wher re are or obstacles to transport in near field. If release is limited by a small hole in canister, buffer/rock transition is little importance. Due to se different conditions, it is really not possible to stipulate any special preferable maximum value groundwater flow on a deposition hole scale (even if it is possible to specify an approximate upper limit where groundwater flow influences release from near field). Extremely large groundwater flows or fracture apertures could damage buffer by creating conditions for its mechanical erosion (SR 97 Process Report /SKB, 1999b/. However, such high flows can, if y occur at all, always be avoided by a suitable choice deposition holes Requirements preferences From a transport viewpoint, re is no reason to make requirements on groundwater flux or apertures on a deposition hole scale. As long as buffer is in place, this toger with solubility limits provides a considerable retardation release from a damaged canister. It is, however, a requirement that flow apertures not be so large that buffer is damaged. Apertures centimetre size are needed for buffer to be damaged. The requirement avoiding fractures with such apertures can always be met by a suitable choice deposition holes. From a transport viewpoint re is a preference for low water flux small apertures. It is refore not possible to specify an upper limit for preferable Darcy velocity (or hydraulic conductivity), but it is preferable that canister positions can be found in a large portion rock which, on a canister hole scale, have a lower Darcy velocity than 0.01 m/y, since lower fluxes entail increased retardation. In any case, however, a final assessment wher near-field properties are good enough needs to be made within framework an integrated safety assessment. 104

101 9.2.3 Generic knowledge knowledge obtained at different stages The Darcy velocity on a deposition hole scale is a calculated parameter. It exhibits considerable spatial variation. In SKB 91 /SKB, 1992/, Darcy velocity in Finnsjön was calculated to lie in range m/y. For various sites (Äspö, Finnsjön, Gideå) that have been analyzed within framework SR 97, calculated Darcy velocities lie within same range (/Walker Gylling, 1998/, /Walker Gylling, 1999/, /Gylling et al., 1999/). The spatial variation within each site is considerable, but values are typically 100 times lower for Gideå compared with or sites. Different regional studies or feasibility studies do not contribute any new knowledge about groundwater flux or fracture apertures at repository depth compared with general knowledge that already exists. In a site investigation, groundwater flow can be calculated by modelling based on permeability that can be estimated from hydraulic tests in boreholes. The modelling results provide statistical information that can be used to judge spatial variation Darcy velocity on a deposition hole scale. There are also methods for direct measurement groundwater flux in a part a borehole /e.g. Rouhianen, 1993/. The methods are useful but y also only provide information in a number points that can be used as a statistical sampling. It is only during detailed characterization or later that individual canister positions can be evaluated Suitability indicators criteria Groundwater flux (Darcy velocity) on a deposition hole scale should be a useful suitability indicator during a site investigation. But preference is not very great importance. In formulating criteria, it is also necessary to take into account uncertainties in estimate spatial variation groundwater flow. Excluding deposition holes with such great groundwater flux such large apertures that buffer function can be adversely affected may be necessary in selecting individual canister positions, but does not influence overall siting since se conditions can only apply to very local areas in rock. Such active choices can, however, not be made until during detailed characterization or a deposition stage. Fracture apertures on a deposition hole scale are only limited importance as suitability indicators, since y are as a rule limited importance for function. No information on groundwater flow on a deposition hole scale is available during feasibility studies. During site investigation, it is judged to be an obvious advantage if estimated Darcy velocity on a deposition hole scale is lower than 0.01 m/y for a large number (in a statistical sense) positions in rock. Neir safety nor retardation in rock need be threatened if criterion is not met, however. In any case, a final assessment near-field properties needs to be made within framework an integrated safety assessment. 105

102 9.3 Properties flow paths Description parameters ir influence on functions The models for transport in rock may undergo development over coming years, which means that parameters used here may change. The fundamental arguments presented here will probably not have to be changed, however, even though it may turn out that methods used today to describe transport underestimate retardation reby exaggerate preferences that should be made on rock from a transport viewpoint. The transport radionuclides through rock takes place chiefly by advection in open fractures. If substances dissolved in water do not interact with ir surroundings, transit time is determined by water s travel time (t w ), which can be expressed as length transport pathway (L) divided by quotient Darcy velocity (q) flow porosity (ε f ). If substances can furrmore diffuse into rock matrix sorb re, this will give rise to a considerable retardation, resultant transport velocity is n determined essentially by Darcy velocity geometry fractures, by diffusion sorption properties matrix. The flow porosity is subordinate importance in this case. If a simplified flow geometry is assumed, e.g. flow through rectangular channels, controlling groups parameters for matrix diffusion can be expressed as product transport resistance or F parameter a group parameters containing sorption coefficient (K d value), diffusion coefficient matrix porosity. The F parameter can be expressed in different ways, for example: F=a r L/q =(a w /ε f )L/q=a w t w where a r is flow-wetted surface area per volume rock a w is flow-wetted surface area per volume flowing water (see e.g. /Andersson et al., 1998b/). The latter formulation is used in model FARF31, which is used in SR 97. The greater transport resistance, greater retardation. It should be noted that a w t w are strongly inversely correlated via ir linear dependence on flow porosity, but that product F is not directly dependent on flow porosity. In addition to advective transport, mixing velocity differences occur in groundwater. This residual term is usually called hydrodynamic dispersion. In groundwater calculations that are performed as a basis for safety assessment, however, advective flow field is described in relatively great detail. Different deposition holes will be connected with different transport pathways. The different transport pathways can have drastically different groundwater flows. The explicit modelling se velocity variations enables somewhat problematical concept dispersion to be minimized to small-scale velocity variations. Dispersion will reby be subordinate importance for radionuclide transport. Dispersion is represented by a Peclet number, where large Peclet numbers mean that dispersion is small compared with advection. The importance some retardation is nuclide-specific. Sorption coefficients (K d values) matrix diffusivity are nuclide-specific (see section 9.4). Furrmore, if retardation is great in relation to nuclide s half-life, nuclide will decay before it has passed through geosphere, whereas if retardation is small in relation to half-life it will have a negligible influence. Due to se relationships it is really not possible to specify any particularly preferable minimum value transport resistance (F parameter). 106

103 From calculations in SR 97, where several different values F parameter were studied in different calculation cases (Main Report, section 9.11 /SKB, 1999a/), general conclusion can noneless be drawn that geosphere has a considerable capacity for retarding important radionuclides if F>10 4 y/m. The importance retardation in geosphere decreases rapidly for lower values. This semi-qualitative assessment also agrees with conclusions that can be drawn from SKI s safety assessment SITE-94 / SKI, 1996/ or different Finnish safety assessments (e.g. TILA-99 /Vieno Nordman, 1999/) Requirements preferences There are no grounds for requirements on F parameter or or flow-related transport parameters. The release to biosphere can be kept below levels set in SSI s regulations even if not all transport pathways from repository to biosphere have a large transport resistance. It is a preference that re be a considerable retardation important radionuclides in geosphere (Figure 9-1). A quantitative preference can be expressed in form transport resistance (F parameter), where Darcy velocity, flow distribution flow-wetted surface area per volume rock (or similar parameters) are such that a large fraction all flow paths have F>10 4 y/m. (At reasonable values a r (1.0 m 1 ) L (100 m), this leads to preference q<0.01 m/y, but account must be taken fact that q a r vary may be correlated, see also section ) In any case, a final assessment needs to be made within framework an integrated safety assessment. There is no reason to make special preferences regarding flow porosity or hydrodynamic dispersion Generic knowledge knowledge obtained at different stages The calculated values F parameter /Andersson, 1999/ used in SR 97 are based on results groundwater flow calculations (/Walker Gylling, 1998/, /Walker Gylling, 1999/, /Gylling et al., 1999/) combined with estimation flow-wetted surface area per volume rock /Andersson et al., 1998b/. The values are shown in Table 9-1. It is clear that all sites contain a large number canister positions connected with transport pathways with F parameter within desired value range. At Äspö Finnsjön re are also several pathways that lie outside value-preferred range. Neverless, SR 97 concludes that safe final repositories can be build on se sites. Furrmore, retardation could be considerably improved if it were possible to deposit canisters only in positions connected with transport pathways with high transport resistance. This option for a greatly improved repository layout has not been taken into account in SR 97 /SKB, 1999a/. Regarding values for or parameters, reference is made to Data Report for SR 97 /Andersson, 1999/. Feasibility studies contribute knowledge on topography an estimate largescale groundwater recharge, which provides some information on groundwater flow transport pathways. Since data on hydraulic parameters are orwise lacking at this stage, it is not possible to obtain a detailed picture groundwater conditions in a feasibility study. 107

104 Figure 9-1. High transport resistance is preferable (low groundwater flow high accessibility to rock matrix). Table 9-1. Calculated values F (y/m) for different flow paths in SR 97 (from Andersson, 1999). Proportion flow paths Äspö Finnsjön Gideå with higher F factor F > F > F > 50% %