Prospective Activities of Regulatory Safety Research and Development on Sub-Surface and Near-Surface Disposal Background of Safety Policies Based on the Risk-informed I. Approach Concerning Sub-Surface and Near-Surface Disposals Planned Concept of Sub-Surface Disposal Facility to be Assessed II. III.  Overview of “Guides for the Safety Assessment of Sub-Surface Disposal after the Termination of the Institutional Control Period (Draft) "' Procedure of  Regulation Support Research and Development on IV. Sub-Surface Disposal Major Current Regulatory Safety R&D on Sub-Surface Disposal V. and Key Technical Issues Prospective Activities of  Regulation Support R&D in the Future VI. February 23, 2010 Hiroto   Kawakami Japan Nuclear Energy Safety Organization (JNES) 1
Safety case and FEP analysis Compilation of results from the analysis of all factors that may affect the safety of disposal facilities and of the arguments that support safety IAEA safety requirement “Disposal of Radioactive Waste” (SSR-5) OECD/NEA international FEP list Optimization of radiation protection within dose constraint and risk constraint for potential exposure - Aggregated approach - Dose/probability disaggregated approach ICRP Pub81 Reactor safety goal 10-6/year Nuclear Safety Commission “Interim Summary of Investigations and Discussions Concerning Safety Goals” (December 2003) Risk-informed approach Nuclear Safety Commission “Common Important Issues of Safety Regulation on Radioactive Waste Disposal” ‘June 10, 2004) Classification of scenarios into three categories Nuclear Safety Commission “Basic Concept of Safety Regulation on Low-Level Radioactive Waste Disposal (Interim Report)” (July 12, 2007) Nuclear Safety Commission  Special Committee on Radioactive Waste and Decommissioning “Guides for the Safety  Assessment of Sub-Surface  Disposal after the Termination of the Institutional Control Period (draft)” 2
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Potential radioactive waste possibility of human intrusion. http://www.nisa.meti.go.jp/ IAEA safety guideline “Classification of Radioactive Waste” (GSG-1) 4 Low frequency (Risk: 10-3 / up to human life) (Occurrence frequency: 10-2-10-1 / assessment period)  Assessment period: 1 million years Compiled from Nuclear Safety Commission “Criteria on Radioactive Waste Disposal in Foreign Countries” (RW 24-1) with some revisions RW: Special Committee on  Radioactive Waste and Decommissioning
MOX fuel Source: Federation of Electric Power Companies “Report on the Progress of Studies Concerning Intermediate oth Disposal" (Document No. 17-4 on Radioactive Was 7
Compiled from: Federation of Electric Power Companies “Quantities and Radioactivity Concentration Levels of Waste for Intermediate Depth Disposal (C2  11-1) C2: Class-2 Waste Disposal Subcommittee of the Nuclear Safety Commission
Operational waste from power stations (activated metal) Waste from JNFL Time after disposal [year] Time after disposal [year] Waste for sub-surface disposal contains significant quantities of nuclides with a long half life. The verification of the safety of sub-surface disposal facilities, therefore, requires the safety assessment over a long period. It is important that the safety assessment should address the impacts from geological uplift, erosion and sea level change if such phenomena are likely to take place around the site in a long term. II.  Report Overview #立行政法人原子力安全基盤機構
Chapter 1 - Introduction Chapter 2 - Setup of Conditions for Long-Term Evolution Concerning the Geological Environment Chapter 3 – Setup of Conditions for Biosphere in the Future Chapter 4 - Setup of Conditions for the Disposal Facilities Chapter 9 – Guides for the Termination of the Institutional Control Period Chapter 10 - Conclusion Technical Document for the Safety Assessment of Sub-Surface Disposal after the Termination of the Institutional Control Period (draft) Translation of this document is tentative for FORUM2010. 10
Щ.  Report Overview - Chapter 2
2.2 Setup of Conditions for Phenomena Caused by Plate Motions 2.3 Setup of Conditions for Phenomena Caused by Climate Change Numbers in blue are section numbers in the report (draft). 2.4.3 Surface water flows 2.4.2 Groundwater flows Stylization of Biosphere based on IAEA International Co-ordinated Research Project  BIOMASS Review Assessment Context Biosphere system pre-defined by explicit legislation or guidance? Principal Component Climate and atmosphere Geographical Biosphere system change to be considered? ldentify and justify selection of mechanisms causing change ldentify potential impacts on the biosphere system Near surface lithostratigraphy ldentify qualitatively different possible futures Select approach to represent biosphere system change Non-sequential Sequential Select appropriate biosphere systems and transitions Select appropriate biosphere systems Describe alternative non-sequential biosphere systems Describe sequential biosphere systems Stylization of exposure pathways in the case of natural events: (1) Pathways of exposure by the use of water from river water, etc. (lake water, river water or stream water) (2) Pathways of exposure by land use (riverside area, terrain covered with sediments from river, dried lake bed, land surface near the uplifted repository, etc.) - Pathways of exposure by land use (by inhabitation) - Pathways of exposure by land use (by construction) Stylization of exposure pathways in the case of inadvertent human intrusion: (1) For residents around the site (exposure pathways do not differ from the case of natural migration) (2) For individual intruders (to be defined specifically) IAEAГ“Reference Biospheres” for solid radioactive waste disposal Report of BIOMASS Theme 1 of the BIOsphere Modelling and ASSessment (BIOMASS) Programme」(IAEA-BÌOMASS、July 2003)
Ш.  Report Overview - Chapter 3 । Step 1 Yes No Describe pre-defined biosphere system (s) Identify and justify primary components of biosphere system(s) s and some server and some server and some server and some server as a server and some server as a server and some server as a server and some server as a server as a server ı Step2 extent Location Describe constant biosphere Topography - system (s) Human activity Water bodies Biota ı Step3 13 hi » INR
Ш.  Report Overview - Chapter 4
Multiple barriers
Щ.  Report Overview - Chapter 5
All pathways of radioactive nuclides to the biosphere must be addressed (considering migration by liquid, gaseous and solid media).
③ Likely scenario for groundwater addressing the period during which natural barrier functions are expected to play a major role - This scenario is used to verify that the protective functions of the natural barriers, assisted by the functions of engineered barrier components with their inherent properties, will play a major role in controlling the dose as low as reasonably achievable. ② Likely scenario for groundwater addressing the period during which safety depends much on multiple barrier functions - This scenario is used to verify that the best available technologies are employed to control the dose as low as reasonably achievable by redundant safety features provided by the engineered and natural barriers. ① Likely scenario for groundwater addressing the transient period - This scenario is used for confirming the reliability of the multiple barriers arriving at intended conditions. - Groundwater in the outside tries to flow into the space  of the engineered barriers. ④ Likely scenario for groundwater addressing the period during which the repository is expected to come close to the ground surface - This scenario is used to verify the absence of any significant residual radioactivity even in the case of the repository coming close to the ground surface, causing the deteriorated repository system to mix with the surrounding soil Likely scenarios are used to perform assessments on highly probable and normally expected events with most probable parameters to verify that adequate measures are taken to control the dose as low as reasonably achievable in each time period. 19
Transient period Assessment of impacts from the radioactive gas and from the generation and migration of radioactive radiolysis gas Period during which safety depends much on multiple barrier functions i. Assessment of impacts from the generation and migration of radioactive gas ii. Assessment of impacts from the generation of hydrogen gas by radiolysis and from the generation and migration of hydrogen gas from the corrosion of metals Period during which natural barrier functions are expected to play a major role Assessment of impacts from the gas generation under the conditions  of physically damaged engineered  barriers and chemical environmental changes Period during which the repository is expected to come close to the ground surface (Independent assessment for radon-related impacts) Waste packages for sub-surface disposal are not expected to contain any radioactive gas except for very small quantities of Tritium and methane gas, but do contain large quantities of metals. Therefore, the impacts of the hydrogen gas from the corrosion of these metals on the integrity of engineered barriers need to be assessed. In addition, in the case of the repository coming close to the ground surface, the impacts of radon, as a progeny nuclide from uranium-series nuclides, need to be assessed.
① Present land use: (if there is any land that can be used after contamination along or around rivers and lakes in the downstream) ② Land use in the case topographical changes due to sea level change need to be considered: Assessment of impacts from the use of dried lake beds in the downstream (impacts from construction and impacts from inhabitation) ③ Land use in the case a terrain covered with sediments from uplift and erosion: Assessment of impacts from the use of a terrain covered with sediments from uplift and erosion (impacts from construction and impacts from inhabitation) ④ Land use in the case the repository is expected to come close to the ground surface: Assessment of impacts from the use of contaminated land (impacts from construction and impacts from inhabitation) Щ.  Report Overview - Chapter 5
Construction -Direct radiation impacts from the excavated spoil Inhabitation -Direct radiation impacts from the excavated spoil Ingestion of crops -Impacts from the ingestion of ① The repository may come closer to the ground surface and to the weathering susceptible zone as a result of phenomena such as uplift, erosion and sea level change. ② It is assumed that, in the weathering susceptible zone, the deteriorated repository system is mixed with the surrounding soil. According to the velocity of uplift, radioactive nuclides are released from the repository system to the weathering susceptible zone. use of river or stream water. The Likely scenario should address land use on the ground surface above or around the closed repository other than groundwater scenario to ensure the verification of the absence of any significant risk from residual radioactivity scenario. Excavation by construction activities The distribution of radioactivity concentration in the weathered zone should be considered
Analysis of factors that cause variations from the likely scenarios - Preparation of plural less-likely scenarios for each likely scenario Completeness in the identification of variation factors - The setup of conditions is preceded by the identification of variation factors by FEP analyses, etc.
Probability and scientific reasonability of variation factors
- If sufficient quantities of statistical data are available, use them to select values in the 97.5% one-sided confidence interval. - If sufficient quantities of statistical data are not available for addressing uncertainties in long-term safety assessment, make the best use of available scientific and technological findings to set up conditions with sufficient allowances based on a conservative approach. - If severale parameters largely affect the assessment results, it is useful to evaluate the uncertainties with such parameters by a probabilistic method to verify reasonability in the setup of conditions
Assessment of the repository system robustness
- A partial loss of safety functions is assumed to verify that the repository system does not depend excessively on any single safety feature. - However, it is not necessary to assume the absence of contributions from the components that have sufficiently demonstrated their reliability or from inherent properties of materials, etc., provides that such contributions are expected to persist through environmental changes, etc. Rather, scenarios should be designed to address uncertainties in long-term safety assessment. Example of statistical data on the distribution coefficient Aoki et al., "Study on un satety assessment part intermediate depth Example dose calculation"  Autumn,
activities Even after including the scenarios that address relatively improbable events, there remain some uncertainties. Rare natural event scenarios are used for verifying that no additional special measure for radiation protection is deemed to be required even after giving attention to such remaining uncertainties.
Procedure of R&D
Analytical study and other work projects previously conducted or participated by JNES in support of the Nuclear Safety Commission FEPC “Quantities and Radioactivity Concentration Levels of Power Station Waste That Exceeds the Upper Bounds of Radioactive Concentration for Near Surface Disposal Specified in the Ordinance" (BD 2- 2-1;  October 21, 2005) JNES and RWMC “Examples for the Classification of Safety Assessment Scenarios Based on the Risk- Informed Approach" (BD 5-Reference 1 ; June 22, 2006) JNES “Examples of Analysis Conducted with Typical Safety Assessment Scenarios for Low Level Radioactive Waste Disposal Facilities" (BD 6- 1; September 19, 2006) Assignment from Subcommittee to Update BD 6-1 in reference to “Upper Bounds of Radioactive Concentration for Burial of Low Level Radioactive Solid Waste” (NSC; May 2007), etc. JNES “Update of Examples of Analysis Conducted with Typical Safety Assessment Scenarios for Low Level Radioactive Waste Disposal Facilities” (C2 7-1; May 2, 2008) in reference to JNES C2 3-2-2 with the inclusion of additional analyses based on comments from committee members FEPC “Quantities and Radioactivity Concentration Levels of Waste for Sub-Surface Disposal (C2 11-1; Sep. 24, 2008) JNES “Reanalysis for the Examples of Analysis Conducted with Typical Safety Assessment Scenarios" (C2 11-2; Sep. 24, 2008) BD: Burial Disposal Subcommittee of  NSC;  C2: Class-2 Waste Disposal Subcommittee of NSC
IV.   Procedure of R&D
Procedure of R&D
Needs of NISA “R&D items to be addressed for meeting the needs” Overall listing of important items that are expected to require NISA's technological judgments in the future Establishment of evaluation methodology for safety features and behaviors of engineered barriers by engineering-scale model (1) “R&D items that remain unaddressed by other institutions" (*) Among the items identified as “R&D items to be addressed for meeting the needs," those which have not been addressed by other institutions are selected. Research and development for the safety of sub-surface disposal of reactor internals, etc.”  Sub-Surface Disposal WG of the Special Committee of JAES (FY2006) ③ “R&D items that are already addressed by other institutions" Among the items identified as “R&D items to be addressed for meeting the needs," those which are already addressed by other institutions are listed. Note (*): The term “other institutions” refers to “institutions other than those which are engaged in regulation support researches." Preparation of data that support safety review Preparation of analytical methodology for cross-checking Preparation of later-stage regulatory procedures such as confirmation of waste package and facility examination ② “Topics that should be addressed by NISA from  an own standpoint” Among the items identified as “R&D items that have been addressed by other institutions,” those which should be addressed by NISA from an own standpoint (e.g. procedures for verifying the acceptability of assessment results produced by the utilities) are listed. Whatever resources that may contribute to the fulfillment of the NISA’s needs should be actively be used or shared after ensuring their qualities to support Safety Regulation. R&D Items to be addressed by regulation support organization in the future Accumulation of domestic and international research results
1. Safety R&D on Groundwater Flow Assessment 2. Safety R&D on Nuclide Migration Assessment 3. Safety R&D on Protection Capability Assessment of Engineered Barriers
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V.1 Groundwater Flow Assessment
Features of 3D-SEEP Ver. 2: ● Three-dimensional analysis of saturated-unsaturated infiltration flows - Finite element method - Supports steady and unsteady state analysis. - Allows consideration of density gradient of seawater, etc. (only in unsteady state analysis mode). -Supports evolutionary changes of boundary conditions such as the water level, seawater level and rainwater recharge. The project (up to FY2010) aims at verifying the analysis code in reference to boring data from a broad area (including both recharge and catchment areas) in the Horonobe region, which is characterized by noticeable geological activities that result in uplift, erosion and sea level change.
V.2   Nuclide Migration Assessment
● Across different layers from the waste package layer to the bedrock, nuclides migrate by advection, dispersion and diffusion. ● Safety assessment is supported by one-dimensional modeling by GoldSim, in which the volumes of the concrete pit structure, low diffusivity layer and low permeability layer are. ● The uniform aggregate layer represents the backfill, support, lining and EDZ outside the low permeability layer under a single grouping. Key technical issues concerning one-dimensional nuclide migration modeling for groundwater scenarios: - Methods for enabling one-dimensional models to achieve equivalent and conservative representation of nuclide migration across a two-dimensional profile by advection and diffusion - Modeling of the degradation of engineered barrier properties by aging and of the cracking of concrete
Key technical issues of addressing changes in migration pathways through natural barriers by one-dimensional nuclide migration modeling: -Spatial changes in migration pathways through natural barriers and the shortening of migration pathways must be represented by changes in the travel length (or time) through natural barriers. -Appropriateness of modeling by the combination of various elements of general purpose simulation code.
Key technical issues concerning multidimensional nuclide migration modeling: ●Pursuit of higher accuracy by the improvement of numerical solution methods (better algorisms for lesser numerical dispersion values) ●Appropriateness of one dimensional modeling of cases in which the line of hydraulic gradient does not perpendicularly go across the length of cavern ●Modeling of entire cavern (assessment of the independency of each cavity; assessment of the probability of interconnection due to EDZ and assessment also of the plug performance) of groundwater flow parallel to the length of cavern In a cavern that does not have partitions, advection and diffusion may cause the radioactivity concentration to increase at the end of cavern. Assessment  of Engineered Barriers V .3 fety R&D on Protection Capability Assessment of Engineered Barriers Assessment of Degradation of Cement Component(s)s ① Leaching of hydrates from cement and the formation of secondary mineral products (Assess the impacts of the formation of pores due to leaching and the impacts of the swelling of secondary mineral products.) ③Impacts of pore water quality (Assess the impacts from salt water, soluble salts and nitrides and sulfides contained in waste package.) ④Degradation by heat (Assess the impacts of heat from waste and the thermal impacts from igneous activities.) Flow direction Host rock EDZ Backfill Engineered barrier and waste package layers Make use of relevant materials such as: Japan Society of Civil Engineers “Guides for the Setting of Nuclide Migration Assessment Parameters for Groundwater Scenarios in the Safety Assessment for Sub-surface Depth Disposal" (June 2008). ② Appearance and growth of cracks due to changes in the stress field or due to degradation (caused mainly by the swelling of reinforcing bars and waste containers due to corrosion) Assessment  of Engineered Barriers V.3
Photo: Bentonite deposit covered by the natural analogue study Bentonite component (s) degradation processes that require attention: ①The loss of compaction and low permeability feature of the bentonite layer with the fall of earth pressure due to uplift, erosion, etc. →  JNES studies various properties of bentonite layers in exposed bentonite deposits (natural analogues). ② Loss of the low permeability feature due to chemical transformation (into Ca- type bentonite) V.3 Assessment  of Engineered Barriers ety R&D on Protection Capability Assessment of Engineered Barriers Understanding of the Ultimate Characteristics of Cement and Bentonite Ultimate characteristics: inherent characteristics that can be still expected from bentonite under severe conditions produced by the combination of multiple degradation processes that should be assumed: - Loss of compaction due to the flowage of bentonite into the pore of degraded cement component(s)s - Fall of earth pressure due to uplift or erosion, resulting in the loss of constraint on the swelling of bentonite - Chemical degradation of bentonite (transformation into Ca-type bentonite) [JNES is now conducting a column test (FY2009-2010).] The test set is used to simulate the flowage of bentonite into degraded cement component(s)s, a process accelerated by the swelling of bentonite by groundwater. The experiment will enable the determination of inherent characteristics specific to bentonite (permeability, in particular) under - Transformation into Ca-type accelerated by cement ingredients
- Engineering-scale (about 1/5) model (more than 100years →about 2) - Understanding of resaturation and gas migration behaviors in the low permeability layer The following should be verified by this experiment for the verification of safety margins for engineered barriers using an engineering- scale model: 1. Stable preservation of the low permeability property → Using the engineering-scale model, it should be verified that the whole layer swells uniformly and the intended low permeability property is achieved without much dependence on local-scale properties. 2. Formation of gas breakthrough pathways by the growing gas pressure → The stress from gas pressure may concentrate at corners of the low permeability layer, producing breakthrough pathways even at a relatively low gas pressure. It should be verified that such will not spoil the integrity of engineered barriers. 3. Restoration of low permeability after the release of gas → It should be verified that breakthrough pathways are closed again and the low permeability property is restored due to the self-sealing property of bentonite.
1. Safety Regulation According to the Level of Potential Hazard from Waste 2. Basic Design Reliability and Repository System Robustness 3. Ensuring of Total Safety Performance Taken in Consideration of Natural Barrier Performance 4. Preparation for Regulation Process after Safety Review
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Based on the risk-informed approach, the safety regulations demand trench disposal, concrete pit disposal or sub- surface disposal depending on the level of potential hazard from each specific type of radioactive waste. The contamination level of operational waste is extremely low because fuel failures are rare in recent light water reactors and the reactor water contamination level is low. Key nuclides in waste for sub-surface disposal are difficult to measure. It is important to improve the accuracy of estimation based on calculations about activation. JNFL: Business License Application for Rokkasho Low-Level Radioactive Waste Disposal Center. Jan. 1997 FEPC : Quantities and Radioactivity Concentration Levels of Waste for Sub-Surface Disposal (C2 11-1; Sep. 24, 2008) Kato et al.,: Current Status of Technical Confidence Building for Sub-surface Disposal (Journal of Nuclear Fuel Cycle and Environment  Vol13 No.1 , P49-64,2006) 48
The overall safety should be ensured by developing the basic design based on reliable predictions on highly probable and normally expected events with conservative approaches to both sides contradictory characteristics
Example of engineered-natural barriers combination that meets the standard dose values and ensuring of total safety performance Migration performance of natural barriers
END