Long-Term Management and Actions for a Severe Accident in a Nuclear Power Plant

Description

Table of contents List of figures List of tables List of authors Lead authors Persons who contributed to the work group Organisations that provided information on long-term management status (cf. questionnaire in Appendix A) and for the action identification and ranking table (AIRT) exercise (Section 3.5) Persons who provided a complete external review of the report Persons who provided a review on specific parts of the report Secretariat List of abbreviations and acronyms Executive summary Chapter 1. Introduction 1.1. Background 1.2. Objectives and scope 1.3. Structure of the report Chapter 2. State of the art of long-term management and actions 2.1. Feedback from Three Mile Island unit 2, Chernobyl and Fukushima Daiichi accidents Synthesis of relevant Three Mile Island unit 2 experience Actions taken during the stabilisation phase Waste water management Decontamination of the buildings and equipment Defuelling Disposal and long-term storage of fuel and other radioactive wastes Worker protection Insights and lessons learnt  New processes and communication with the public  Decontamination and management of radioactive waste and effluents  Risk management and occupational safety  Method and equipment development Synthesis of relevant Chernobyl experience Characterisation of dose rates, contaminations and releases Countermeasures undertaken in the short term and their effects Fuel debris bed characterisation and isolation Activities associated with the safety of the sarcophagus  Characterisation of fuel-containing materials  Criticality control of fuel and corium in the shelter (Sarcophagus)  Studies of debris and lava ageing  Spent fuel pools  Water management in the sarcophagus Countermeasures related to the sarcophagus radiation safety  Long-term management of damaged fuel and wastes  Long-term water and solid waste management Summary of long-term management of the Chernobyl accident Synthesis of relevant Fukushima Daiichi experience Generalities on long-term management and recovery actions at Fukushima Daiichi Present knowledge of PCV and RPV status Containment overview and identified major leakage paths RPV status and estimated degraded fuel location Regulatory framework and implementing long-term management plans Approaches to risk for long-term management  Risk mapping  Risk assessment  Risk reduction strategy  Analytical approach to risk  Long-term management for risks reduction in relation to plant damaged states  Monitoring and strengthening of safety systems for long-term management  Contaminated water management actions  Solid waste management actions  Management of spent fuel pools Unit 4 Unit 3 Unit 1 Unit 2  Countermeasures against external hazards Earthquakes and tsunamis Fires Severe rain and typhoons Tornadoes  Site boundary dose rate, mitigation of dust dispersion, improving working environments Monitoring results Dose evaluation at the site boundary Mitigation of dust dispersion Work environment improvement  Site inspection  Preparation of defuelling actions  Summary of main implemented countermeasures Reactor cooling Spent fuel removal Contaminated water treatment Radioactive waste Radiation protection Earthquake and tsunami countermeasures Improvement in work environment  Summary of main issues and challenges at Fukushima Daiichi Regulatory framework Approaches to risk Management of contaminated water Fuel removal from spent fuel pools Fuel debris retrieval Solid waste management Work environments 2.2. Status of long-term post-accident management and actions in NEA member countries Existing, envisaged or planned regulation for long-term management in NEA member countries Belgium Canada Czech Republic Finland France Germany Japan Korea Slovenia Spain Switzerland United States Identified critical safety functions for long-term management Identified measures and actions for long-term management Procedures and guidelines Human and organisational resources Equipment, infrastructure and instrumentation Approaches, methods and tools for long-term management and actions assessment Chapter 3. Approach to long-term post-accident management and actions 3.1. Definition and scope 3.2. Long-term controlled state functions and monitoring Long-term management functions to maintain a controlled state Reactivity control Decay heat removal Mitigation of radioactive releases Prevention of combustible gas explosions Monitoring quantities needed for LTM controlled state functions 3.3. Possible accident/plant damaged states classification for long-term management Situations with very limited release to the environment during the emergency phase Plant damaged state 1 (PDS-1): severe accident with intact RPV and containment Situations with limited or controlled releases to the site and environment during the emergency phase PDS-2: SA with failed RPV and containment maintained without venting PDS-3: SA with failed RPV and limited or controlled releases (leakage of the containment or filtered venting) Situations with significant uncontrolled releases to the environment during the emergency phase PDS-4: SA with failed RPV and failed containment PDS-5: SA with failed RPV and failed containment by MCCI (for some designs) PDS-6: SA with containment bypass (e.g. steam generator tube rupture in PWR and liner melt-through in BWR Mark I and Mark II containments) PDS-7: SFP accident Aggravating factors Summary and conclusion 3.4. Methods and tools for risks and issues ranking for long-term management Introduction to a structured approach to risks ranking and issues identification General approach to issues and risks identification Scenario categorisation and analysis for conducting risk assessment and issues ranking Issue categorisation and analysis for conducting risk assessment and issues ranking Introduction and main components of a general structured layout approach Long-term management goals Fuel debris heat removal Brief description of the issue Reference situations and deviation types  Fuel debris heat removal: Working conditions Brief description of the issue Reference situations and deviation types  Fuel debris heat removal, ongoing accident evolution (non-system-related cliff-edge effects) Brief description of the issue Reference situations and deviation types  Fuel debris heat removal, new accident conditions Brief description of the issue Reference situations and deviation types Mitigate radioactive releases  Mitigate radioactive releases: Gas emissions Brief description of the issue Reference situations and deviation types  Mitigate radioactive releases. Liquid effluent emissions Brief description of the issue Reference situations and deviation types  Mitigate radioactive releases: Decontamination of highly contaminated floors and walls Brief description of the issue Reference situations and deviation types Prevention of risk of explosions  Prevent risk of explosions: Monitoring Brief description of the issue Reference situations and deviation types  Prevent risk of explosions: Clearing Brief description of the issue Reference situations and deviation types  Prevent risk of explosions: Removal Brief description of the issue Reference situations and deviation types Defuelling preparation and completion  Preparation for defuelling: Collection of information Brief description of the issue Reference situations and deviation types  Preparation for defuelling: Training Brief description of the issue Reference situations and deviation types  Preparation for defuelling: Defuelling operations Brief description of the issue Reference situations and deviation types  Preparation for defuelling. Safety requirements Brief description of the issue Reference situations and deviation types Issue identification and risk ranking methods 3.5. Action identification and ranking table exercise Introduction, scope and objectives Elicitation process Individual process of assessment Likelihood of success Technologically available/knowledge issue: Tools Available on-site/logistics: Provisions Operable/constraints: Accessibility Technology gaps Collective process of assessment Presentation of the results Comments and results of the action identification and ranking tables General preliminary aspects Comments and results 4) Maintain coolable configuration and manage confinement Inject water in-vessel Inject water in containment RPV pressure control Maintain RPV integrity Containment pressure control Containment hydrogen control Confinement of fission products Minimise environmental release (airborne and aqueous) Minimise likelihood of criticality Maintain SFP cooling and minimise risk 2) Water waste, solid waste, and effluent management Minimise and collect contaminated water Decontaminate collected waste water Recirculate decontaminated water for core cooling Collect and store waste water Monitor and control fission products including tritium in water Control and minimise effluent discharge Effluent characterisation Collect, store solid wastes and monitor fission product contents Storage and disposal of filtered containment venting system water and filter 3) Site clean-up and decontamination Plant site clean-up and rubbles/sludge removal (outside of the reactor) Surface decontamination Rubbles and sludge characterisation Monitor cooling pond (and sea) contamination Monitor and control groundwater contamination Radiological monitoring Characterisation of fission products distribution in contaminated spaces 4) Defuelling of damaged reactors Detect fuel debris locations and estimate debris masses (at start of defuelling) Identify state of degraded fuel/fuel debris including control rod and structural material Collection of damaged fuel/debris samples and characterisation Fuel debris examination and characterisation for storage Minimise environmental release during defuelling 5) Damaged fuel/fuel debris and radioactive waste disposal, SFP fuel removal Temporary on-site storage of damaged fuel/fuel debris Temporary on-site storage of structural debris Temporary on-site storage of filters used in water decontamination process Material control and accountability SFP defuelling 6) Long-term management Radiological and security monitoring on-site Occupational health protection Emergency equipment maintenance Risk assessment related to LT actions External hazards assessment and countermeasures Conclusions derived from the AIRT exercise results Chapter 4. Summary of challenges and main issues for long-term management Regulatory and organisational aspects Relation to the public during long-term management Risk evaluation for long-term management Radioprotection in long-term management Coolable configuration and confinement of radioactivity Development and use of unique systems, equipment and instrumentation Contaminated water treatment Site clean-up, de-contamination and waste management Fuel retrieval Chapter 5. Recommendations for enhancing long-term post-accident management and for future research 5.1. Recommendations related to knowledge consolidation for cross-cutting issues Calculation tools and methods for severe accident analysis in reactor and spent fuel pool Status of equipment, systems and structures in the long term of a severe accident Severe accident long-term phenomena Methods or systems for risk assessment for long-term management 5.2. Recommendations related to provisions development for cross-cutting issues Enhance monitoring of plant damaged state and of long-term management actions Upgrades of components, equipment, systems and structures Develop harmonised practices and technical means to limit workers occupational exposure during long-term management 5.3. Recommendations related to knowledge consolidation for specific long-term management Maintaining long-term cooling Maintaining sub-criticality Limiting radioactive releases Site clean-up, decontamination and wastes management Fuel retrieval and disposal 5.4. Recommendations related to provisions developments for specific long-term management and actions Appendix A. Questionnaire on long-term management and actions for a severe accident in a nuclear power plant Background information Appendix B. Simplified application of SA-LT categorisation from level 2 probabilistic risk assessment release category figures of merit Level 2 probabilistic risk assessment release categories as a starting point Transformation process from level 2 PRA RC into SA-LT PDS Application Removal of source term release related classification criteria SA-LT PDS minimal safety functions SA-LT PDS coupled with minimal safety functions configurations Thermal-hydraulic sequences linked to each SA-LT PDS minimal safety functions configuration Appendix C. Fault tree analysis and event tree analysis Appendix C. SA-LT management schematic guiding procedure Mitigating system status trees Long-term critical safety pillars status trees Mitigating system fault tree analysis/event tree results References