Regulations on Severe Accident in Korea

Transcription

1 IAEA Technical Meeting on the Verification and Validation of Severe Accident Management Guidelines December 12-14, 2016 IAEA Headquarters, Vienna, Austria Regulations on Severe Accident in Korea Ku Young CHUNG Department of Severe Accident and Risk Assessment KINS

2 Contents Historical Backgrounds Responses to Fukushima Accident Rulemaking on Severe Accident Concluding Remarks 2

3 TMI Accident (1979) Historical Backgrounds (1) The first severe accident of NPP in human history. US NRC ordered licensees to implement more than hundred Post-TMI action items after TMI accident to enhance safety of NPPs against severe accident (1980). Korea s response after TMI accident Regulatory authority ordered the licensee to implement Post-TMI action items of US NRC (1983) Severe accident mitigation measures for new reactors were continuously strengthened, including hydrogen control after severe accident (~ 1990s). Probabilistic Safety Assessments (PSAs) for some operating reactors and all new reactors were performed. 3

4 Historical Backgrounds (2) Severe Accident Policy (2001) establishes safety goals (quantitative health objectives), requires PSA for all operating and new reactors, requires design features for new reactors to prevent severe accident and, should it occur, to mitigate its consequence, and requires development and implementation of severe accident management program (SAMP) for all operating and new reactors. Implementation of SAP by administrative orders PSAs for all reactors were completed and safety improvements identified by PSAs were implemented. SAMPs for all reactors were developed and in use. Design features for prevention and mitigation of severe accident are applied to the new reactors. 4

5 Responses to Fukushima Accident (1) Special Inspections by Regulatory Body (~ May 2011) Inspection teams organized by regulatory inspectors and external experts 21 operating nuclear power plants and 1 research reactors Objectives of the Special Inspections Design and operation measures against natural disasters Mitigation capability against severe accident Effectiveness of emergency response system Enforcement order to implement 50 action items to address issues identified by the inspection To minimize the impact of extreme natural phenomena To make emergency power and ultimate heat sink available To prevent and mitigate severe accidents 5

6 Responses to Fukushima Accident (2) The regulatory body of the Korean government, Nuclear Safety and Security Commission (NSSC) reviewed the effectiveness and the status of Fukushima Action Items (March 2014) Based on the review results, NSSC issued supplemental administrative order for the licensees to implement additional 3 action items (March 2014) : Additional Action Items Improving the emergency response measures against man-made disasters as well as natural disasters Operating an dedicated emergency response organization for severe accident management Securing emergency response center to protect emergency workers and to secure equipment and systems for command and control 6

7 Responses to Fukushima Accident (3) NSSC decided to require Stress Tests for old plants (April 2013) Objectives Evaluation of coping capability against large scale natural disasters that beyond design basis Scope Wolsong Unit 1 and Kori Unit 1 (more than 30 years of operation) NSSC decided to expand the scope of Stress Tests to include all operating NPPs (Sep. 2015) Phase 1 Perform Stress Tests for a few selected NPPs that can represent various designs of all operating NPPs Phase 2 Prioritization of the rest of NPPs considering their plant-specific aspects in comparison with the results of Stress Tests for the representative NPPs Stress Tests for the rest of the NPPs focusing on the plant-specific aspects 7

8 Rulemaking on Severe Accident (1) Background of the Amendment of NSA Previous regulatory activities on severe accidents were on the basis of administrative orders. After Fukushima accident, National Assembly decided that regulation on severe accident should have clear legal basis. Amendment of Nuclear Safety Act (2015) The National Assembly amended the Nuclear Safety Act to clearly stipulate the regulatory control on severe accident. The amendment requires that Accident Management Program (including severe accident management) shall be submitted in the application of operating license of NPPs. The effective date of the amendment is 23 June, The amendment also requires that AMPs for existing (operating) reactors shall be submitted to the NSSC within 3 years after the effective date. 8

9 Rulemaking on Severe Accident (2) Subsequent rulemaking after the Amendment of NSA to support the amendment of NSA, subsequent rulemaking was done to amend the presidential decree, the prime ministry s decree and NSSC rules (June 2016). Major elements of the rulemaking include; Requirements on the contents and acceptance criteria for AMP, including safety goals, accident management strategies, procedures and guidelines to control accidents, licensee s staffing, education and training, etc. Requirements on design features and mitigation strategy to prevent and mitigate severe accidents resulting from multiple failures of safety systems as well as from extreme natural or man-made hazards Requirements on assessment of environmental impact from severe accidents 9

10 Rulemaking on Severe Accident (3) Basic Concept for Accident Management Definition of Accident Management by Nuclear Safety Act A set of actions to prevent the escalation of accidents, to mitigate the consequence of accidents and to recover a nuclear power plant from accident conditions Adoption of IAEA s Defense in Depth (DiD) Concept Level Plant State (Accident Condition) Management Measures Design Basis Accident Single failure of Safety System Design Basis Event (Seismic, Flood, ) Engineered safety features Emergency procedures Prevention of Severe Accident Multiple failure of Safety System Extreme natural/man-made hazards SA prevention features SA prevention guidelines (3) recovery Mitigation of Severe Accident Core melt-down SA mitigation features SA mitigation guidelines (1) Prevention of escalation (2) Mitigation of consequence New rules explicitly introduce additional two levels of defense, the prevention and mitigation of severe accident. 10

11 Rulemaking on Severe Accident (4) Accidents considered in the prevention level Accidents from multiple failures ATWS, Station black out, Accidents from extreme natural/man-made hazards Tsunami, Aircraft impact, Capabilities to control accidents from multiple failures Design/operational measures to prevent the significant damage of fuel in reactor core or spent fuel pool Capabilities to control accidents from extreme hazards Strategy and measures (including mobile equipment) to recover and maintain safety functions including core cooling, SFP cooling, 11

12 Rulemaking on Severe Accident (5) Phenomena considered in the mitigation level Hydrogen explosion Over pressure/temperature of the containment Fuel-coolant interaction, Capabilities to control severe accident phenomena To maintain containment integrity against severe accident phenomena by control of hydrogen, To prevent large release of radioactive materials to the environment 12

13 Rulemaking on Severe Accident (6) Amendment of Presidential Decree requires regulatory inspection on the implementation of AMP Amendment of Prime Minister s Decree stipulates the contents of AMP; The scope of accidents and equipment to control them Accident management strategies Accident management implementation Evaluation of accident management capabilities Education and training Amendment of NSSC rules for regulation of NPPs The scope of accidents; Multiple failures (Station Black-out, ) Beyond-design-basis external events (seismic, aircraft impact, ) Severe accident (means accident with significant damage of reactor fuel) 13

14 Rulemaking on Severe Accident (7) Amendment of NSSC rules for regulation of NPPs (cont d) The equipment used in AMP shall perform its intended function in the accident conditions Accident management strategies shall recover and maintain safety functions essential to the prevention and mitigation of severe accidents Implementation of accident management includes staffing, command and controls, maintenance of equipment, preparation of procedures/guidelines to implement accident management strategies, etc. Evaluation of accident management capabilities shall verify : Prevention capabilities against multiple failures and BDBEEs Mitigation capabilities against severe accidents Capabilities to limit the expected radiation dose at the plant boundary consequence analysis of severe accident is required. Probabilistic safety assessment 14

15 Rulemaking on Severe Accident (7) Amendment of NSSC rules for regulation of NPPs (cont d) Procedures and guidelines for accident management consists of emergency operation procedures : cover DBAs and Multiple Failures extreme hazard mitigation guidelines : cover beyond design basis external events severe accident management guidelines : mitigate severe accident Regulatory reviews on the procedures and guidelines will cover technical bases V&V processes and results education and training programs 15

16 Concluding Remarks Significant improvements for the safety of NPPs against severe accidents have been made since Fukushima Daiichi accident, which are based on the various responses of the regulatory body to the accident. As required by the amendment of the Nuclear Safety Act in 2015, rulemaking for the regulatory control of severe accident including SAMG was recently completed to improve the consistency and the predictability of the regulatory control of severe accidents. 16

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