Development of the NUMO pre-selection, site-specific safety case

Transcription

1 P.0 Development of the NUMO pre-selection, site-specific safety case 24 th November 2016, Vienna, Austria International Conference on the Safety of Radioactive Waste Management, IAEA Nuclear Waste Management Organization of Japan (NUMO) Tetsuo Fujiyama, Satoru Suzuki, Akira Deguchi, Hiroyuki Umeki

2 Evolution of geological disposal programme in Japan P.1 In 1999, the H12 Report was published by JNC (now JAEA), which demonstrated the feasibility of safe geological disposal of HLW based on a generic study. On the basis of the H12 Report, the Final Disposal Act for implementing geological disposal of HLW came into force and NUMO was established in NUMO initiated the siting process by open solicitation of volunteer municipalities in ILW (termed TRU waste in Japan) was also included in NUMO s remit by amendment of the Act in The Great East Japan Earthquake and the Fukushima Dai-ichi NPP accident in 2011 increased nationwide concerns about the feasibility and reliability of geological disposal in Japan No volunteer municipality has appeared and no candidate host rock type has been specified as yet.

3 Why make the NUMO Safety Case? P.2 The Basic Policy, based on the Final Disposal Act, was amended in 2015, which involves that the Government will nominate scientifically suitable areas to initiate discussions and cooperation with local municipalities, finally leading to acceptance of a site investigation, which will be carried out by NUMO. It is important at this time to present technical evidence to support the feasibility and safety of geological disposal, which will encourage stakeholder support of implementation NUMO has developed the NUMO pre-selection, site-specific safety case Development of site descriptive models (SDMs) on the basis of field data obtained at URLs, provides a more advanced site-specific basis than the H12 Report.

4 Staged site investigation process Literature Investigation Stage Literature survey Preliminary Investigation Stage Surface based investigations Detailed Investigation stage Surface based investigations Investigations in the UIF Investigation and evaluation of the geological environment Exclusion of unsuitable sites Estimation of geological environment characteristics Development of SDM Exclusion of unsuitable sites Understanding geological environment characteristics Update of SDM Confirmation that site is suitable Detailed understanding of geological environment characteristics Update of SDM Repository design Outline of initial repository concept Preliminary design of disposal facility Basic design of disposal facility Safety Assessment Outline of safety assessment Preliminary safety assessment Basic safety assessment Selection of PI areas Planning of PI stage Selection of DI areas Planning of DI stage Selection of the repository site Development and review of the safety case P.3

5 Providing the basic safety case structure At this stage Nationwide literature Literature Investigation Stage Literature survey Preliminary Investigation Stage Surface based investigations Detailed Investigation stage Surface based investigations Investigations in the UIF Setting of candidate host rock type Exclusion of unsuitable sites Exclusion of unsuitable sites Confirmation that site is suitable Development of SDM Estimation of geological environment characteristics Understanding geological environment characteristics Detailed understanding of geological environment characteristics Trial design of repository Development of SDM Outline of initial repository concept Update of SDM Preliminary design of disposal facility Update of SDM Basic design of disposal facility Trial safety assessment Outline of safety assessment Preliminary safety assessment Basic safety assessment Next technical development plan Selection of PI areas Planning of PI stage Selection of DI areas Planning of DI stage Selection of the repository site The basic safety case structure Development and review of the safety case P.4

6 Documents and target audience P.5 For geological disposal experts For others The geological disposal community Engineers & Technologists Scientific communicators General public Executive summary 30 pages NUMO Safety Case Report Main Report 350 pages Supporting Reports Detailed background to support the main report 178 documents, Total 4800 pages Reference R&D reports NUMO-TR, JAEA-Research, CRIEPI-Reports, Scientific papers etc. Abridged report (Describing mainly key messages of SC with simple text, 50 pages) Why geological disposal? Basic concept of geological disposal Basic Safety strategy Stepwise approach Reversibility Transparency PR materials (brochures) Principles and safety of geological disposal Existence of suitable geological environments Safety in case of natural hazards Pre-closure safety Retrievability of waste Presented using a web-based communication platform

7 Contents of NUMO Safety Case report P.6 1. Background and purpose 2. Safety strategy 3. Geological characterisation and synthesis...developing geo/hydro models of potential host rock environments on the basis of the state-of-the-art geoscientific knowledge 4. Repository design and engineering technology...being performed on the basis of the models, providing underpinning evidence to demonstrate the technical feasibility of geological disposal 5. Assessment of pre-closure safety 6. Assessment of post-closure long-term safety...being performed on the basis of the models, providing underpinning evidence to demonstrate the long-term safety of geological disposal 8. Confidence in the technical feasibility of geological disposal in Japan 9. Conclusions

8 Five rock types 7

9 Nested models for plutonic rocks Highly fractured (weathered) domain Sedimentary overburden Granite GW flow Fractured media Hard rock Active fault 1 km Illustrative geological setting 100~200 m 100~200 m Active fault L 1 km Regional scale (50 km x 50 km) L 1 km Repository scale (5 km x 5 km) L 10 m Panel scale (800 m x 800 m x 800 m) P.8

10 Nested models for Neogene sedimentary rocks P.9 Granite Quaternary sediments (several tens of m) Porous media with low density of fractures Soft rock GW flow Active fault Basement 500 m Freshwater saline water transition Illustrative geological setting Active fault Sea L 25 m Regional scale (30 km x 30 km) Repository scale (5 km x 5 km) Panel scale (800 m x 800 m x 800 m)

11 Nested models for Pre-Neogene sedimentary rocks P.10 Quaternary sediments (several tens of m) GW flow Thrust Fractured media with high density of fractures Hard rock 1000m Freshwater saline water transition Sea Illustrative geological setting Regional scale (40 km x 40 km) Repository scale (5 km x 5 km) Panel scale (800 m x 800 m x 800 m)

12 Repository concepts to be considered in design study P.11 Concrete support 支保工 HLW repository Vertical emplacement Vitrified waste ガラス固化体 Overpack オーバーパック TRU waste repository Vault waste emplacement Concrete support Pit Backfill Waste packages Backfill 埋め戻し材 Disposal hole 処分孔 (EBS) ( 処分坑道 ) ( 人工バリア ) Prefabricated EBS module (PEM) Buffer 緩衝材 Disposal drift Overpack Vitrified waste PEM Buffer (Bentonite) Backfill Buffer (Bentonite) Metal shell

13 An example of underground panel layout 5 km Plutonic rocks model Unpreferable area Short travel time Faults (Length > 1 km) 予備区画 (TRU) 区画 4 予備区画 2 Required scale of the facility: Total HLW: more than 40,000 canisters of vitrified waste 予備区画 4 区画 6 区画 1 区画 2 予備区画 1 Total TRU waste: more than 19,000 m m 予備区画 3 区画 5 区画 3 Relative migration time + Direction of ground water flow P.12

14 Assessment of long-term post-closure safety P.13 Since safety standards for geological disposal in Japan have not, as yet, been defined, the results of the safety assessment are compared to international standards. A risk-informed approach is introduced, based on international guidelines as well as recent national discussions on safety regulations. Referring to the guidelines of international organisations on assessment timescales, dose calculations are carried out for up to one million years after closure. The advanced approach and methodology for radionuclide transport modelling can be used to compare different sites and disposal concepts.

15 Scenario classification and target dose P.14 Scenario classification Likely Scenario Less-likely scenario Very unlikely scenario Human intrusion scenario Definition This scenario is used to assess the performance of the geological disposal system based on the best understanding of the probable evolution, as a reference for the optimisation of protection. This scenario is used to assess the safety of the geological disposal system in view of uncertainties in scientific knowledge supporting likely scenarios. Possible scenarios with extremely low likelihood. This scenario is used to check whether the geological disposal system is robust with assumption of human intrusion after loss of institutional control. Target dose Target value: 10 μsv/y Safety reference value: 0.3m Sv/y Reference value: 1~20 msv/y Reference value; Residents: 1~20 msv/y Intruder: 20~100 msv/event

16 3D modeling of RN transportation 100m Rock EBS 100m Buffer k= m/s Backfill (Bentonitesand mixture) k= m/s Deposition hole Cross section of drift Shotcrete t=50 mm k= m/s (degraded) EDZ t=1000mm Fracture transmissivity:100 times to the original value Drain k= m/s EDZ t=500mm Faults and fractures are represented by stochastic modelling approaches, on the basis of the site-specific dataset obtained URLs. A 3D model is used to represent the geometry of the EBS components and geosphere to realistically evaluate transportation of RN at the near-field scale. P.15

17 Examples of safety assessment of HLW P.16 Plutonic rock model Maximum dose rate (μsv/y) 1E-4 1E-3 1E-2 1E-1 1E+0 1E+1 1E+2 1E+3 1E+4 1E+5 H12 Report - reference case Likely scenario case / Plutonic rock Uncertainties in glass dissolution rate Likely scenario (10 μsv/y) Bentonite alteration due to Fe-silicate minerals Uncertainties in fracture distribution Less-likely scenarios (300 μsv/y) Change of magnitude of hydraulic gradient Uncertainties in radionuclide migration parameters (Kd, De) of rock Concealed active fault intersects the repository Human intrusion (exploration) Very unlikely scenarios (1~20 msv/y) Human intrusion scenarios

18 Progress since H12 report P.17 Development of realistic SDMs on the basis of key characteristics, e.g. distribution of faults, fractures and their hydraulic conductivities, in particular from studies in Japanese URLs since A practical methodology for tailoring repository design to geological environments Engineering feasibility of technology for retrieving waste Pre-closure safety assessment of radiological protection during waste handling in surface facilities The advanced approach and methodology for radionuclide transport modelling can be applied to compare different site and disposal concepts Development of management strategy for project implementation (Quality Management, Knowledge Management, R&D, Strategy on human resources )

19 Key conclusions P.18 The NUMO pre-selection, site-specific safety case provides the basic structure for subsequent safety cases that will be applied to any selected site, emphasising practical approaches and methodology which will be applicable for the conditions/constraints during an actual siting process. The preliminary results of the design and safety assessment would underpin the feasibility and safety of geological disposal in Japan.

20 Schedule for the NUMO SC report P.19 January 2017 Finalisation of NUMO Safety Case report (for review, in Japanese) Open to the public on a web-based communication platform Start of domestic review by the Atomic Energy Society of Japan Around July 2017 Finalisation of the NUMO Safety Case report (for review, in English) reflecting comments from domestic and international experts Application for international review (by OECD/NEA?)

21 Thank you for listening P.20