Poster [LE] Laboratory Experiments

Transcription

1 Poster [LE] Laboratory Experiments

2 P-LE-01 DI-B EXPERIMENT : PLANNING, DESIGN AND PERFORMANCE OF AN IN SITU DIFFUSION EXPERIMENT IN THE OPALINUS CLAY FORMATION A. Yllera 1, A. Hernández 1, M. Mingarro 1, A. Quejido 1, L.A. Sedano 1, J.Soler 2, J. Molinero 3, J.M. Barcala 1, P.L. Martín 1, P. Wersin 4, P. Rivas 1, P. Hernán 5 1. CIEMAT, Avda. Complutense 22, Madrid, Spain 2. CSIC-ICTJA. Martí i Franqués s/n, Barcelona, Spain 3. UDC-ETSICCP. Campus de Elviña s/n, La Coruña, Spain 4. NAGRA. Hardstrasse 73, CH-5430 Wettingen, Switzerland 5. ENRESA. Emilio Vargas 7, Madrid, Spain The DI-B experiment is a Spanish project led by ENRESA aimed to study the hydrogeochemistry and transport mechanisms in the Opalinus Clay formation at the Mont Terri Underground Research Laboratory (Switzerland). The Mont Terri URL is under the patronage of SNHGS, managed by the GI and financed through the Mont Terri Consortium (SNHGS, ANDRA, BGR, ENRESA, GRS, IPSN, JNC, NAGRA, OBAYASHI and SCK CEN). In relation to the geochemical behavior of the Opalinus Clay, one of the key aspects that has to be addressed for repository safety assessment purposes is to understand the transport mechanisms of the radionuclides contained in the radioactive waste. Consolidated clay formations display very low water hydraulic conductivities, so it is expected that the predominant transport process will be diffusion. With regard to the understanding of transport mechanisms the DI-B experiment comprises the following activities : - to design and perform an in situ diffusion test, employing non-radioactive tracers, - to perform a set of laboratory tests aimed to provide relevant data both for the preliminary modeling and for the in situ experiment, - to perform a modeling exercise with the data obtained from the in situ diffusion test. The DI-B diffusion experiment consists in a single-point dilution test by injecting stable tracers into a packed-off section at the bottom of a vertical 7.7m depth borehole. Surface instrumentation has been designed to circulate the anoxic synthetic water through the injection section and to allow for tracer injection and sampling. Hydraulic pressure is kept constant during all the experimental time to avoid transport processes other than diffusion. The disappearance of each tracer versus time in the water reservoir is monitored during the experiment by periodical sampling and chemical analysis. After one year of diffusion time, the experimental section is overcored, sampled (3-D), sliced and the tracers content is analyzed for the later 3-D modeling. The whole system has been designed for monitoring and recording several physicochemical parameters (ph, conductivity, oxidation-reduction potential), the pressure in the circuit and for the long distance monitoring of the data acquisition system. The tracer selection has been made based on previous investigations carried out at CIEMAT, including a literature survey, laboratory sorption experiments and hydrogeochemical modeling for determining their stability under the physicochemical conditions to be expected in the site. The final selection includes 6-Lithium, 87-Rubidium, Deuterium and Iodide. Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 267

3 P-LE-01 Diffusion and sorption experiments have been carried out at laboratory scale with Opalinus Clay samples to provide diffusive and sorption parameters for modeling purposes. Preliminary diffusion calculations have been carried out by using several transport codes: GIMRT (CSIC-ICTJA); CORE 2D (UDC-ETSICCP) and CODE-BRIGHT (CIEMAT). The three groups performed their predictions employing different mathematical tools (discretization by finite elements or by finite differences) and also considering several conceptual and geometrical approaches. The tracers considered for modeling were either conservative or non-conservative. The effective diffusion coefficients (D e ) obtained from the calculations showed slight variations, which were consistent with the different modeling approaches employed. The predictive modeling results have been used to determine the initial tracer concentration that must be added into the circuit in order to assure well-defined profiles at the end of the experiment. This long-term in situ diffusion experiment will also provide useful data for the interpretation of previous diffusion experiments performed at the Mont Terri URL. ENRESA and NAGRA have financed this work. Page 268 Clays In Natural And Engineered Barriers For Radioactive Waste Confinement

4 P-LE-02 THE RESEAL PROJECT A LARGE SCALE SHAFT SEALING DEMONSTRATION TEST Bernard Dereeper, Geert Volckaert SCK CEN, Boeretang 200, 2400 Mol, Belgium In September 1999, SCK CEN started a large scale shaft sealing test in the frame of the EC RESEAL project. The small shaft of the HADES URF (Mol, Belgium) was used for this experiment. This one was constructed in as a test case- to demonstrate that an excavation work is possible in unfrozen plastic clay at a depth of more than 225 m. About 15 years later, this shaft is used to demonstrate the feasibility of another important item of the underground radwaste repository building, the sealing of shaft. Most of the radwaste disposal scenarios consider that any opening created during the repository construction has to be sealed effectively afterwards. The objective of the test is to demonstrate that it is possible to seal this 2.2 m diameter opening in the Boom clay and the excavation disturbed zone around it with a granular material composed of bentonite powder mixed with highdensity bentonite pellets. This material has the advantage that it can be easily applied to backfill irregularly shaped volumes and that it is rather cheap to produce in comparison to compacted blocks. Figure 1 gives a general overview of the shaft sealing test. The shaft has been backfilled with concrete up to a depth of about 16 m. On top of this backfill zone the bentonite seal has been installed after removal of the shaft liner. It was essential to remove this liner, much more permeable than the Boom Clay to effectively seal the shaft. The clay seal has a height of 224 cm and a diameter of Figure 1 : General overview of the shaft about 220 cm and consists of FoCa clay pellets and powder mixed at a weight ratio of 50/50. An industrial compactor especially designed for the project by CEA has been used for the compaction of this mixture on the first 60 centimetres of the seal. This compacted layer has a density of about 1.55 g/cm³. On the upper part of the seal, the powder/pellets mixture has been applied without further compaction to avoid damage to the instrumentation installed in the seal. This uncompacted layer has a density of about 1.4 g/cm³. The top and the bottom of the clay seal have been made water and gas tight by a resin layer. The seal is instrumented with relative humidity sensor, porewater pressure sensors and also with total stress and displacement sensors. One year before the seal installation, several drillings have been made at different distances from the shaft and instrumented in order to get a three dimensional picture of the stress Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 269

5 P-LE-02 distribution around the seal. The in situ hydraulic and mechanical perturbations and the displacements caused by the installation of the seal and its subsequent swelling are monitored. The observations made during the seal installation and the following period of natural and artificial hydration will be described and commented. The in situ hydraulic and mechanical perturbations caused by the installation of the seal and its subsequent swelling were monitored. In spite of the fast installation of the seal minimising the potential displacement of the host rock, the removal of the liner caused an important hydro-mechanical perturbation of the surrounding host rock. This one is larger than expected especially the fissuration up to at least 1 m distance radially from the shaft wall. The combined effect of the self-healing properties of the plastic Boom Clay and the current hydration of the bentonite seal should help to restore the perturbation. The hydration of the seal was started early May 2000 and is still running. The water inflow rate, the pore water pressure and the total pressure evolution in the seal are currently monitored. Once the seal is saturated, various tests will be performed to check its performances, i.e. water permeability tests, gas breakthrough experiment, tracer diffusion test inside and around the seal and a hydraulic shock to simulate accidental pressurisation conditions. In order to assist in the interpretation of the measurements and to validate our understanding of the hydro-mechanical and transport behaviour of the seal, numerical predictive modelling are being performed by two partners, UPC and CEA. Besides, at the end of the test all the results -the experimental and calculated ones- will be reviewed with regard to the sealing performance assessment and confidence building by ANDRA. This should lead to an increased confidence on performance of geological disposal in clay. Acknowledgements The shaft sealing test is performed in the frame of the EC RESEAL project (4 th and 5 th EURATOM framework programme) and financially supported by NIRAS/ONDRAF and EC (contract nr FIKW-CT ). Page 270 Clays In Natural And Engineered Barriers For Radioactive Waste Confinement

6 P-LE-03 PRODUCTION & EMPLACEMENT OF GRANULAR BENTONITE MATERIAL ENGINEERED BACKFILL (EB) EXPERIMENT IN OPALINUS CLAY MONT TERRI URL, CH Keith Kennedy 1, Franz. Verfuss 2, Michael Plötze 3 1. NAGRA, Hardstr. 73, Wettingen, CH, kk@nagra.ch - Corresponding author - 2. DMT, Essen, DE 3. IGT-ETH Zurich, CH For radioactive waste repository settings, a variety of engineered barrier configurations are being evaluated for the buffer materials which would extend from the canister to the walls of the tunnel s geologic media. The role played by this engineered barrier is an important one that frequently involves clay minerals. The role of this buffer is also related to the expected canister design and performance which varies among international radioactive waste programs. The EB experiment is a demonstration project funded by three project partners (BGR, ENRESA and NAGRA) and the EU and the Swiss Government. An integrated approach was used to develop the team s overall objective of evaluating performance of an engineered barrier in a tunnel/canister setting similar to a repository setting. The new aspect of the barrier being investigated in EB is combined use of blocks and a granular mixture (GBM) both made from bentonite that extends from the canister to the tunnel walls. Three of NAGRA s four specific roles were to 1) evaluate options and methodology for producing granular bentonite material at a near-commercial scale, 2) design and build equipment to remotely emplace GBM in tunnels and 3) emplace and determine effective density of GBM in the EB tunnel setting at Mont Terri. The approach to the EB experiment bentonite processing and emplacement of the granular backfill mixture was based on results from NAGRA s prior work undertaken at a smaller scale in the mid-1990s when boreholes in granite were sealed with MX80 materials injected pneumatically. This earlier work showed that production of a mixed grain size materials at a laboratory scale was possible with density (dry) in the coarse fraction about 2.2 gm/cm 3 and in the boreholes to 1.5 gm/cm 3. New material-related aspects of the project included addressing options in dryness, grain size and rounding variability to achieve increased emplaced density. New production-related activities addressed scaling 250-fold from backfill material volumes of 200 L to 50 m 3 reflecting the requirement to eventually fill the ca. 6 m long 2.5 m high and 3 m wide horseshoe shaped experimental EB tunnel New equipmentrelated project features undertook a feasibility assessment approach to optimizing remote emplacement by expanding the options to include conveyor and auger mechanical methods as well as the pneumatic technique. Production and emplacement trials using about 45 T of calcigel bentonite from Süd-Chemie (DE) were done first. The calcigel was able to be ground to up to about 5 mm size and then dried using a relatively routine industrial approach to about 6 to 7 percent water content but above our desired target of 4 percent. The production of the granular mixture involved first making pellets in a roller press with the objective being to achieve 2.0 or greater dry density in the pellets produced in a commercially available roller pressing process. Following this, grinding and breaking of these pellets was done to meet two different grain size specifications. One mixture represented sizing similar to the Fuller/Simonis curve, one which Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 271

7 P-LE-03 is typically referred to for obtaining optimized density without compaction requirements. The second mixture evaluated a bimodal distribution with grain sizes of both 0.4 mm to 2 mm and 5 mm to 15 mm. Additional mixing was done with both grain size fractions in a subsequent post production pilot scale step using two mechanical methods to identify which distribution achieved the higher density. Emplacement trials were done in a wooden model scaled to represent the upper half of the EB tunnel. The preferred alternative identified from the model filling with all three methods was the auger technique. Density results for the auger were marginally better than for the pneumatic method but with greater homogeneity and dramatically reduced dust generation. Actual EB tunnel emplacement involved filling about 28 m3 of remaining space with FEBEX-type (Serrata) bentonite. This material was chosen to closely correspond to that of the blocks underlying the canister. Specialty drying by IKO Minerals (DE) reached 3.3 % water content. Pellets had a dry density of 2.1 gm/cm 3. The bimodal grain size material water content was 4.2 % after secondary mixing. Single auger remote delivery rates were about 3 m 3 /h. Our results suggest that in real repository conditions an average emplaced granular dry density of from 1.3 to 1.4 gm/cm 3 can be readily achieved. With optimization in both the material production process and emplacement equipment the density range should increase to from 1.4 to 1.5 gm/cm 3. Page 272 Clays In Natural And Engineered Barriers For Radioactive Waste Confinement

8 P-LE-04 DEVELOPMENT OF EQUIPMENT, MATERIAL AND TECHNIQUE FOR BACKFILLING TUNNELS IN A NUCLEAR WASTE DISPOSAL David Gunnarsson, Lennart Börgesson Clay Technology AB, IDEON, Lund, Sweden In the main concept for disposal of the Swedish Nuclear Waste (KBS-3V) it is vital that the drifts can be backfilled with sufficiently good material at high density to fulfil the following requirements : - to obstruct upwards swelling of bentonite from the deposition holes, - to prevent or restrict the water flow in the tunnel and around the canister, - to resist chemical conversion for a long period of time, - not to cause any significant chemical conversion of the buffer surrounding the canister. Investigations and tests of backfill material and techniques have been running in the Swedish hard rock laboratory, Äspö HRL, since1996. At first the objectives were to test the manufacturing of backfill material, to develop and test a suitable backfilling technique and to investigate what densities could be achieved with different backfill materials in the field. Horizontal layers were applied and compacted by a roller in 0.2 m thick layers to 1.5 m from the floor. The rest of the tunnel was backfilled with inclined layers using a modified standard vibrating plate compactor carried by a tractor with a telescopic arm. Five different backfill materials were tested; TBM-muck, TBM-muck crushed to a maximal grain size of 20 mm and crushed TBM-muck mixed with 10, 20 and 30 % MX-80 bentonite. The main conclusions from these tests were that the technique for manufacturing backfill material and for backfilling the tunnel were suitable but that the horizontal backfill layers were sensitive to wet conditions, that the backfilling equipment needed to be improved to better reach the areas close to the rock walls and roof and that the durability of the equipment needed to be improved. For the continued testing for the Backfill and Plug Test it was decided that the backfilling should be made with inclined layers in the entire cross section of the tunnel in order to make the technique less sensitive to water. The backfilling equipment was improved; two new compactors, the so-called slope compactor and the so-called roof compactor, were developed and manufactured and a new carrier was chosen. Two different backfill concepts were tested in the Backfill and Plug Test : 1. the entire cross section was backfilled with 0-20 mm crushed rock mixed with 30 % MX-80 bentonite (referred to as 30/70). The material close to the roof was compacted with the roof compactor, 2. the tunnel was backfilled with 0-20 mm crushed rock (referred to as 0/100). The roof compactor was not used. Instead a gap of about 10 cm was left at the roof and filled with bentonite blocks and pellets. Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 273

9 P-LE-04 The compaction sequence for the 30/70 material is shown in Figure 1. a) d) b) e) c) f) Figure 1. : Compaction sequence: a) bringing material into the tunnel, b) pushing it in place, c) compacting the material at the roof, d-f) compacting the rest of the layer The conclusions were that the backfilling equipment worked well both in terms of function and in achieving the intended densities. To achieve optimal density in the entire cross section of the tunnel the operator of the backfilling equipment has to be skilled. Factors such as irregularities in the roof, instruments and rock reinforcement also affected the backfill density close to the roof. The dry density of the backfill a few dm from the roof, were it was most difficult to reach high densities, was above 1.5 ton/m 3 in the areas were the backfilling was not disturbed by instruments. The average measured dry density in the 30/70 was 1.70 ton/m 3. Based on this the average dry density is estimated to be between 1,65 and 1.70 ton/m 3. The average measured dry density of the 0/100 was 2.17 ton/m 3 Page 274 Clays In Natural And Engineered Barriers For Radioactive Waste Confinement

10 P-LE-05 UNDERGROUND TESTING AND INSTRUMENTATION IN ENDURATED CLAY FORMATIONS J.L. García-Siñeriz 1, J.L. Fuentes-Cantillana 1, J.C. Mayor 2, F. Huertas 2 1. AITEMIN. Alenza, Madrid, Spain 2. ENRESA. Emilio Vargas, Madrid, Spain Clay formations are one of the candidate geological structures considered in the Spanish AGP concept for the definitive storage of highly radioactive nuclear waste. Clay presents a high diversity of conditions both from the geological and the geomechanical points of view, but in general the main advantages of this type of formations, compared with other potential structures such as crystalline rocks, are their low permeability and their relative homogeneity. On the other hand, the very important coupling existing in clay between the hydrogeological and geomechanical aspects, makes that some processes, such as ventilation and heating, require a special attention in the design and the safety assessment of the repositories. Also the effect of the repository excavation itself is much higher than in other more competent rocks. ENRESA has been conducting a number of research activities on these topics during the last years, specially in connection with different experiments taking place at the Mont Terri underground laboratory in Switzerland, that are carried out through an international collaboration scheme. So, the Heating Experiment (HE) aims to the improved understanding of the effect of the residual heat of the waste in the hydrogeological and mechanical conditions of the rock, and the interaction between the rock and the engineered barrier; The Ventilation Experiment (VE) tries to identify the effect of the ventilation in the rock around the repository galleries, and the Engineered Barrier Experiment (EB) is focused to analyse the feasibility of constructing a bentonite barrier in an in-drift disposition, using a pellet-based backfill. Some of these projects have been running since some yeas ago, and also in some of them there have been a number of unexpected difficulties in terms of the understanding of the behaviour of the clay formation, specially from the hydrogeological point of view. The paper describes the objectives of these tests, their configuration, and the experiences gained so far. Special emphasis is put on the instrumentation aspects, which in some cases has required a novel approach. Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 275

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12 P-LE-06 OVERVIEW OF HORONOBE URL PROJECT : PRELIMINARY RESULTS OF HYDROGEOLOGICAL INVESTIGATIONS Nobuhisa Ogata, Toyo Ogawa Japan Nuclear Cycle Development Institute, 4-33, Muramatsu, Tokai, Ibaraki, , Japan As part of feasibility study on the geological disposal of high-level radioactive wastes, Japan Nuclear Cycle Development Institute (JNC) has been performing research into soft sedimentary rocks at depth. The town of Horonobe is located at the northernmost part of Japan, and the construction of an underground research laboratory is scheduled there in a tertiary sedimentary rock at a depth of about 500 m. This is one of the main research facilities in which researches into reliability of waste disposal technology will be examined, along with those related to the establishment of safety evaluation techniques. It is also an important test site, where necessity of the research and development must be fully understood by the Japanese people. In the next score, geological science will be studied at the Horonobe URL, together with the study of geological waste disposal techniques. The research period is divided into three stages: surface investigation (1st stage); investigation during construction of research tunnels (2nd stage); and experiments in the URL facilities (3rd stage). One of the main research objectives is to construct geological environment models that can be used for designs and performance assessment; they consist of geological, hydrological, mechanical, and geochemical models. During a period between late 2001 and early 2002, the 2nd year in the 1st research stage, two-700 m boreholes have been drilled, and the rock cores have been retrieved along the length of the holes. Carried out so far have been the tests on mechanical and physical properties, thin-section analyses, X-ray diffraction analyses, water analyses, fossil analyses, and so on (The results of the tests are reported in an accompanying paper in the conference). The rock cores have been eye inspected for the geological description of the diatomaceous mudstone. Geophysical explorations, such as density, caliper, temperature, spinner, and EMI logs have also been performed in the boreholes, with measurements of in situ horizontal stresses by hydrofracturing, and hydrological tests by the pulse and the slug methods at selected depths. This paper introduces the overall research schemes of the Horonobe URL project, and the current situation of the investigation is described. Of all the field investigations performed so far, geological descriptions obtained from the core logging, the results of the in situ initial stress measurements, and the hydrological test results are discussed in detail. Based upon the test results obtained, research themes for the future study are summarized. Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 277

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14 P-LE-07 EXPERIMENTAL EVALUATION OF THE TERMO HYDRO - MECHANICAL BEHAVIOUR OF THE FRACTURES IN TOURNEMIRE SITE (FRANCE) Amel Rejeb Institut de Radioprotection et de Sûreté Nucléaire, avenue du Général Leclerc, B.P. 6, Fontenay-aux-Roses Cedex, France, amel.rejeb@irsn.fr The Institute of Radioprotection and Nuclear Safety (IRSN) fulfils a mission of research and expertise in safety assessment for deep underground storage of nuclear waste for French governmental authorities. It has selected the Tournemire site in order to study the confining properties of argillaceous media. The Tournemire site is characterised by a sub-horizontal indurated argillaceous layer, 250 m thick of Jurassic argilites and marls. These geological series are located between two limestone aquifers. A 2 km long old railway tunnel gives access to the argillaceous layer. Recently, in 1996, two 30 m long drifts were excavated perpendicularly to the old tunnel. This geotechnical context allows us to compare the mechanical evolution of a 100 years old tunnel with 6 years old drifts. In addition, one of these two new drifts (western drift) crosses a fractured zone, which provides the opportunity to analyse the stability of these underground constructions in two different structural configurations. Three types of fractures were identified on the Tournemire site. The first type includes preexisting tectonic fractures and faults filled by calcite. The second type of fractures resulted from the mechanical decompression of the rock mass surrounding the tunnel and the drifts following their excavation. These fractures are subvertical or oriented at 45 (shearing angle) with an extent around 2 m in the tunnel and 40 cm in the drifts. The third type of fractures appeared on the front faces and the walls of new drifts shortly after the end of their excavation. They result from the desaturation of the rock being in contact with an unsaturated atmosphere. Their orientation differs from what expected for classical mechanical fractures. They are nearly horizontal and follow the stratification of the rock material, with rather regular 20 cm spacing. They are closed during the summer and they are opened during the winter. The same phenomenon is observed in the tectonic and the mechanical fractures. The aim of this paper is to describe the instrumentation of these fractures and to present the evolution of their deformations with the seasonal variations in the site. In each drift, six fractures, covering the three types presented above, are selected and instrumented using electric extensometers installed perpendicularly to each fracture. These extensometers record ten times per day the opening and the closing of the fractures. Around each extensometer, two sensors are installed to record respectively the evolution of the temperature and the humidity. The analysis of the hole measurements recorded between 1999 and 2002, has provided the following major results : - a clear correlation between the fractures deformation and the variation of the temperature and the humidity is established. The fractures close in summer at wet and hot atmosphere and open in winter at dry and cold atmosphere as it is shown on the examples of figures 1 and 2, - the closing-opening fracture mechanism varies between 0.1 and 3 mm for a temperature range of [6, 16 C] and a humidity range of [40, 100%], Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 279

15 P-LE-07 - the deformation of fractures located in the western drift is more important than the one of the fractures in the eastern drift. The maximal closing measured in the fractured drift is 3 mm against 1 mm recorded in the unfractured drift. A more important difference is obtained between the convergence measurements in the two drifts. As expected, the fracture system makes the rock mass less stiff in the western drift, - the amplitude of the measured deformation depends on the nature of the fractures. In fact, the tectonic fractures exhibit the maximum closing-opening, followed by the mechanical and the desaturation ones. A data processing, by using statistical correlation methods, allowed the determination of a set of correlation functions linking the deformation of each fracture first to the temperature, second to the humidity and finally to the time. The analysis of the two first derived functions provides respectively the amplitude of the thermal dilatation coefficient and the hydric transfer coefficient. In addition, the last correlation function provides a quantitative evaluation of the reversibility of the opening-closing mechanisms. Figure 1 : Example of correlation between fracture deformation and temperature IRSN - Tunnel de Tournemire - Galerie Ouest Evolution de l'écartement de la fissure et de la température en fonction du temps GOFS29TA fissure GOTR300A température 2,0 20,0 1,5 18,0 1,0 16,0 Variations d'écartement (mm) 0,5 0,0-0,5-1,0-1,5 14,0 12,0 10,0 8,0 6,0 Température ( C) -2,0 4,0-2,5 2,0-3,0 0,0 01/04/ /07/ /09/ /12/ /03/ /06/ /09/ /12/ /03/ /06/ /09/ /12/ /03/2002 Ouverture de la fissure si écartement croissant Figure 2 : Example of correlation between fracture deformation and humidity Date IRSN - Tunnel de Tournemire - Galerie Ouest Evolution de l'écartement de la fissure et de l'humidité relative en fonction du temps GOFS29TA fissure GOHR300A humidité relative 2,0 100,0 1,5 90,0 1,0 80,0 0,5 0,0-0,5-1,0-1,5-2,0-2,5-3,0 01/04/ /07/ /09/ /12/ /03/ /06/ /09/ /12/ /03/ /06/ /09/ /12/ /03/2002 Variations d'écartement (mm) 70,0 60,0 50,0 40,0 30,0 Humidité relative (%) 20,0 10,0 0,0 Ouverture de la fissure si écartement croissant Date Page 280 Clays In Natural And Engineered Barriers For Radioactive Waste Confinement

16 P-LE-08 USING EVIDENCE - BASED LOGIC TO DESIGN INVESTIGATIONS FOR CLAY BARRIER SYSTEMS R. Metcalfe 1, H. Takase 1, M. Toida 2, Y. Suyama 2, K. Kawano 1, A. Bowden 1, D. Savage 1 1. Quintessa Limited Queen s Tower A 7-707, Minatomirai, Nishi-ku, Yokohama, , Japan 2. Kajima Coroporation, 19-1, Tobitakyu, 2-Chome, Chofu-shi, Tokyo, , Japan Modelling the performance of the clay component within an engineered barrier system is particularly challenging because account must be taken of many imperfectly understood physical and chemical processes and complex interactions between them. Thus, for any given barrier system, and any given purpose many decisions must be taken when designing the most appropriate model and investigations to supply the information required to support the model. For example, it is necessary to decide, among other things: the most appropriate numerical algorithms; the most reasonable minerals to incorporate; the most appropriate thermodynamic data; and the most appropriate geometry. To make such decisions requires that uncertainties are properly taken into account, notably uncertainties in: the nature of the processes themselves (e.g. pore-fluid mineral interactions under high swelling pressures); the data used to parameterize the model (e.g. kinetic rate constants); and uncertainties caused by the need to simplify the actual model (e.g. the need to represent complex solid solutions by end-member mineral compositions). Particularly, in the context of investigations related to radioactive waste management, it is important that these decisions are made in a well-structured, thoroughly documented fashion while considering the underlying uncertainties adequately. In recent years the hydrocarbons and minerals industries have made successful use of evidence-based logic to develop structured process models for guiding and documenting exploration decisions, while evaluating relevant uncertainties. Here, we suggest how this approach can also be applied for guiding the many decisions that must be made when developing modelling and investigation strategies for engineered clay barrier systems. A hierarchy of processes is constructed, from the process of interest, to the sub-processes that influence this process (Figure 1). The evidence for the top-level process, that is the degree to which it is dependable or not, is judged by propagating evidence for the sub-processes upwards in the hierarchy, by considering three parameters: 1.) sufficiency, the weighted contribution of the evidence for a sub-process to a higher process; 2) dependency, the degree of overlap in the sources of the evidence for the process; 3) necessity, a Boolean operator describing the evidence without which the top process cannot be achieved. Alternative models are compared using three-parameters comprising evidence for, evidence against and remaining uncertainty (Figure 1). This evidence-based method can be used to : I. integrate data and expert judgement in developing models and investigations, II. identify explicitly the uncertainties within the clay barrier being modelled, III. explore the significance of features or processes through sensitivity analysis, IV. provide comparative analysis between alternative models to allow ranking, Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 281

17 P-LE-08 V. identify the most cost effective areas for targeting data acquisition to build confidence/reduce uncertainties, by identifying those sub-processes that have the greatest influence on the residual uncertainty of the highest level process (i.e. ways to reduce the un-shaded box in the top-level process in Figure 1 by the greatest amount). Assessing the longterm integrity of a clay barrier Success: Predicted integrity consistent with insitu validation experiment 0.20 [0.70,0.10] Assessing observations from analogues [0.1,0.1] To other sub-processes, e.g. assessing observations from man-made analogues (e.g. archaeological evidence), assessing observations from natural analogues etc Assessing output from numerical models [0.77,0.05] Assessing output from generic numerical models Assessing output from purposedesigned numerical models Residual uncertainty [0.85,0.05] [0.20,0.10] [0.85,0.05] Figure 1 : Evidence for To other sub-processes, e.g. assessing kinetic data, Evidence against assessing thermodynamic data, etc Schematic illustration of the application of evidence-based reasoning to developing a simple model for one aspect of clay barrier performance. Numbers are illustrative only. Those next to nodes indicate dependency, those next to lines indicate the sufficiency of the sub-processes. In this process model, no sub-process is a necessity. Evidential support is indicated by the bars. A key feature is that uncertainty due to lack of evidence is distinguished. Page 282 Clays In Natural And Engineered Barriers For Radioactive Waste Confinement

18 P-LE-09 PHYSICAL PROPERTIES OF CALLOVO - OXFORDIAN ARGILLITES AND OXFORDIAN LIMESTONES FROM A BOREHOLE OF THE M / H - M UNDERGROUND LABORATORY SITE Maria Zamora 1, Béatrice Yven 2, Rachel Jorand 1, Alexandre Amiral 1 1. Institut de Physique du Globe (GdR ForPro), 4 place Jussieu, Paris, France 2. Andra, Parc de la Croix Blanche, 1-7 rue Jean Monnet, Châtenay-Malabry Cedex, France Thermal conductivity and velocities of elastic waves were measured on twenty-three samples of Callovo-Oxfordian argillites and Oxfordian limestones from the Est205 borehole of the M/HM underground laboratory. The samples were distributed between the surface and 500 meters depth and are representative of the Callovo-Oxfordian argillites and Oxfordian limestones lithologies. V P and V S were measured with a standard ultrasonic technique in cylindrical samples with a length of 30 cm and a diameter of 10 cm. The thermal conductivity was measured at room temperature, with the divided bar technique, by measuring the temperature gradient for five cylinders (3 cm of length) with variable thickness (2-10 mm). To minimize the effect of contact resistance, thermal conductivity tests were run under uniaxial stress of 10 MPa. All these measurement were made in natural saturation conditions. In the Callovo-Oxfordian argillites P- and S-wave velocities range from 3010 to 4360 m s -1 and from 1570 to 1840 m s -1 respectively. These values are similar to those obtained by sonic log (figure 1) in spite of the fact that the laboratory frequency was three orders of magnitude superior to the sonic log frequency. These rocks display transverse anisotropy, ranging from 2 to 20 %. The V P /V S ratio increases with depth, going from 1.77, at 400 m depth, to 1.95 at 500 m. Thermal conductivity in the vertical direction ranges from 1.1 to 1.5 W m -1 K -1. Thermal conductivity in horizontal direction is 1.8 times higher than vertical direction. In Oxfordian limestones P- and S-wave velocities range respectively from 2290 to 5560 m s -1 and from 1300 to 2940 m s -1. This large range of variation is a consequence of an important variation of the porosity (5 to 20 %) and of the mineralogical composition. Vertical thermal conductivity ranges from 1 to 2.6 W m -1 K -1. As well as in the carbonates that in the argillites, P- and S-wave velocities are linearly correlated with thermal conductivity (figure 2). As a consequence, these laboratory measurements, combined with the sonic velocity profiles, issued from downhole recordings, furnished depth profiles of thermal conductivity in the well Est205 (figure 3). Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 283

19 P-LE Figure 2 : Thermal conductivity as a function of P-wave velocity in carbonates and in argillites Depth (m) Depth (m) V PZ (km/s) Figure 1 : Elastic P-wave velocities obtained in laboratory (squares) and by sonic log (solid line) as a function of depth Thermal conductivty (W m -1 K -1 ) λ = V P R= V P (m/s) λ (W m -1 K -1 ) Figure 3 : Calculated thermal conductivity profile (solid line) compared with the laboratory measurements. The squares and circles represent respectively the vertical and horizontal conductivities Page 284 Clays In Natural And Engineered Barriers For Radioactive Waste Confinement

20 P-LE-10 THE IN-SITU GAS MIGRATION TEST (GMT) AT THE GRIMSEL TEST SITE : RESATURATION PHASE OF SILO TYPE REPOSITORY K. Ando 1, T. Adachi 1, A. Fujiwara 1, S. Vomvoris 2, P. Marshall 2, B. Lanyon 3, S. Yamamoto 4, A. Shimmura 4 1. Radioactive Waste Management Funding and Research Center, No.15 Mori Building , Toranomon, Minato-ku, Tokyo, , Japan 2. NAGRA, Hardstrasse Wettingen, Switzerland 3. Fracture Systems Ltd, Tregurrian Ayr, St. Ives, Cornwall, TR26 1EQ, UK 4. Obayashi Corporation, , Konan, Minato-ku, Tokyo , Japan Focusing on an advanced disposal system for relatively long-lived radionuclides wastes, an assessment should be made of the influence of hydrogen gas generated from the waste corrosion and migrated through the Engineered Barrier System (EBS as a composite system of sad/bentonite-concrete), to the system's behavior. More confident evaluation of gas behavior in and around the facility is considered to be essential for design and construction of the disposal system and its performance assessment. In order to expand its experience in this area with field tests under in-situ conditions, RWMC proposed the GMT as a part of the Grimsel Phase V project (Fig. 1) in 1997 with following objectives, i) assess the function of the EBS and adjacent geosphere as a whole with respect to repository-generated gas migration; ii) evaluate models (conceptual and numerical) applicable to gas migration through barriers under realistic in-situ conditions; iii) provide data for further improvement of the EBS design with respect to gas migration; iv) demonstrate the construction and the emplacement of a EBS under realistic in-situ conditions. The saturation phase of system represents the first stage of field test of the composite system. The aim of the saturation phase is to saturate both the EBS and the immediate geosphere around the GMT cavern, prior to gas injection. After the completion of saturation a short water test is planned to determine effective properties before gas is injected. The saturation of the EBS was initiated in August Parameters monitored are the pore pressure, total pressures, temperature and volumetric water changes with Time Domain Reflectometries (TDRs). The saturation started with an injection period from the bottom layer (which is a sand layer) followed by injection in the top - backfill shown in Figure 1. The injection target pressures are about 5 to 6 bars. The interpreted water content throughout the sand/bentonite in February 2002 is shown in Figure 2. The available data all support a picture where the layers around the top of the concrete silo are close to saturation. The middle layers are moving towards saturation. The bottom layers are now reacting to the higher injection pressures but this is partly due to the influence of higher effective stresses with changes in volumetric water content and pressure that are due to compression or compaction of the material and the consequent reduction in porosity. Pressures have stabilised in the upper cavern backfill at approximately 550 kpa with the injection of approximately 1400 l/day. For the most part this water is out-flowing through the excavation disturbed zone and a shear zone intersecting the cavern, access drift and tunnel in the vicinity of GMT. Nevertheless, the higher head gradients acting are expected to force water into the less saturated layers. Until now re-saturation phenomena is experimentally performed and modelled. Further modelling of the latest data (now in progress) will allow better forecasts of the future progress of the saturation. Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 285

21 P-LE-10 Fig. 1 : Test image Fig. 2 : Volumetric water content of sand/bentonite Page 286 Clays In Natural And Engineered Barriers For Radioactive Waste Confinement

22 P-LE-11 INTEGRATED PROGRAMME OF RESEARCH INTO THE BEHAVIOUR OF THE CLAY ENGINEERED BARRIER : AN EXAMPLE FROM NAGRA'S GRIMSEL TEST SITE I.G. McKinley, W.R. Alexander, W. Kickmaier, C. Biggin Nagra (National Co-operative for the Disposal of Radioactive Waste), Hardstrasse 73, 5430 Wettingen, Switzerland Most designs for the disposal of radioactive wastes include bentonite clay as part of the engineered barrier system (EBS). Generally, the EBS is characterised by the use of large quantities of rather simple, well-understood materials, leading to increased confidence in the predicted long-term behaviour of the EBS (see, for example, Alexander and McKinley, 1999). Despite this, several open questions remain and some of these are being examined at Nagra's Grimsel Test Site (GTS) in the central Swiss Alps as part of an integrated, international study programme (GTS Phase V: see for details). Three specific projects within GTS Phase V are currently investigating the performance assessment (PA) implications of the behaviour of bentonite in the EBS. In the first, demonstration of the overall practicability of the Spanish reference disposal concept (where canisters are placed horizontally in bentonite backfilled tunnels) for high level waste (HLW) is amongst the goals of ENRESA's 1 full-scale EBS experiment (FEBEX). In the second, RWMC 2 are examining the potential effects of gas migration through a bentonitesand mixture surrounding a concrete silo in the Japanese concept for intermediate level waste (ILW) in a large-scale EBS experiment (GMT). Finally, Nagra 3 is investigating the effects of bentonite colloid mitigated migration of radionuclides at the EBS/geosphere boundary where the assumption is that bentonite colloids could be produced by erosion of the bentonite backfill (CRR). Although all three projects have produced significant advances in the understanding of the behaviour of the clay EBS under in situ conditions, they are based on first generation conceptual designs and so, in the planned Phase VI of the GTS, it is proposed to move on and consider more optimised EBS designs, emplacement techniques and even potential alternatives to clay-based EBS. Particularly novel aspects of Phase VI will be : - the integration of a wide range of individual experimental projects in a single theme, - the greater emphasis on the requirements of implementers and regulators during the operational and pre-closure monitoring phases, - consideration of operational phase perturbations, 1 Along with the EU and Nagra 2 With Nagra and Obayashi Corp. of Japan 3 In partnership with ANDRA, JNC, Sandia, ENRESA and FZK-INE Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 287

23 P-LE-11 - planned work with a wide range of safety-relevant radionuclides (an unique feature of the GTS), - increased weighting on full-scale demonstration of operational procedures. In terms of the second aspect, this is a response to the all too frequent occurence of project teams in specific experiments losing sight of the final aims of the work and tending towards more academically interesting, but less PA relevant, areas. During the early stages of concept demonstration and generic feasibility studies, it was obviously necessary to build-up a base of system understanding but this is now fairly well established. The challenge is to integrate such understanding to provide the basis for implementation of practicable, safe and costeffective repository projects which receive wide acceptance from all key stakeholders. To facilitate integration, focus will be narrowed to concentrate in particular on the operational and post-closure monitoring phases of repository implementation. Nevertheless, to ensure that optimisation preserves the critical long-term safety margins required, key aspects of long-term performance of the clay (and non-clay) EBS and immediately surrounding host rock will also be examined. Within the paper, these aspects will be discussed at length and the proposed long-term EBS experiments examined and the advance on current experiments noted. Page 288 Clays In Natural And Engineered Barriers For Radioactive Waste Confinement

24 P-LE-12 CONFINEMENT OF RADIONUCLIDES BY CLAY LAYERS AT THE RUSSIAN DEEP WELL INJECTION SITE AT KRASNOYARSK-26 Stephen M. Wickham 1, Matthew J. White 1, J. Leslie Knight 2, Andrei I. Rybal chenko 3, Evgene N. Kamnev 3, Gennady A. Okunkov 3 1. Galson Sciences Ltd., 5 Grosvenor House, Melton Road, Oakham, Rutland LE15 6AX, UK 2. United Kingdom Nirex Limited, Curie Avenue, Harwell, Didcot, Oxfordshire, OX11 ORH, UK 3. VNIPIPT, 33 Kashirskoje Shosse, Moscow , Russia The European Commission Fifth Framework BORIS project ran from November 2000 to July The overall goal of BORIS was to use data and samples from the Russian borehole injection sites for liquid radioactive waste at Krasnoyarsk-26 and Tomsk-7 to further understanding of the chemical behaviour and migration of radionuclides in the geological environment. A subsidiary goal has been to archive historical data from the sites, thereby ensuring its preservation. At the Russian sites, the migration behaviour of many radionuclides, and the effectiveness of clay layers in isolating radionuclides, can be studied in a natural groundwater system at repository depths. The project has sought to use this information to build scientific and societal confidence in radioactive waste disposal safety assessments and the deep disposal concept. In this presentation, we focus on information from the Krasnoyarsk-26 site on the eastern side of the Yenisey River, about 50 km northeast of the city of Krasnoyarsk. The geological structure comprises an erosional syncline filled with an interbedded mixed sequence of weakly-cemented, permeable Jurassic sandstones and relatively impermeable clays. The syncline has a maximum depth of 550 m below the surface and is bounded on the west by a north-south striking fault called the Rightbank Fault. The principal aquifer horizons in the Jurassic sediments comprise sandstones with multiple clay interbeds, and are named Horizon I and Horizon II, located at depths of m and m respectively. These horizons were selected as reservoir formations for waste disposal. Since the mid-1960s, liquid HLW and ILW have been injected into Horizon I, and liquid LLW into Horizon II. At Krasnoyarsk- 26, the total waste injected comprises 38 million m 3 having a 1998 activity of 450 million Curies. The injected inventory mostly comprises short-lived beta- and gamma-emitting radionuclides, and the waste is expected to remain isolated from the surface environment for at least 1,000 years. The movement of waste solutions within Horizon I and Horizon II has been monitored in detail using an array of approximately 150 monitoring wells. Suites of geophysical well logs from these monitoring wells document the performance of the clay horizons in confining radionuclides, over the time since waste injection started in the mid-1960s. The logs include resistivity and gamma measurements taken before waste injection that may be used to define fine-scale lithological structure, including the presence and thickness of clay interbeds. A series of gamma logs for various monitoring boreholes, recorded at successive times since waste was first injected, documents the development of radioactive plumes and their lateral and vertical migration with time. The gamma logs provide a quantitative measure of the degree to which vertical migration of radionuclides has been prevented by clay layers. An Clays In Natural And Engineered Barriers For Radioactive Waste Confinement Page 289