Nuclear Safety Standards Committee

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The 57th meeting of the Nuclear Safety Standards Committee focuses on the development and application of Level 2 Probabilistic Safety Assessment for Nuclear Power Plants. The agenda includes steps taken to ensure coherency and consistency with relevant IAEA Safety Standards, incorporating feedback from Fukushima-Daiichi nuclear accident, and the status of the document preparation process.

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Nuclear Safety Standards Committee 57th Meeting, [4 6 June 2024] Agenda item 4.4 Development and Application of Level 2 Probabilistic Safety Assessment for Nuclear Power Plants (DS528) - Step 11 TO: Jorge LUIS HERNANDEZ Safety Assessment Section Division of Nuclear Installation Safety

Summary 2

Background IAEA Safety Guide SSG-4 on Development and Application of Level 2 Probabilistic Safety Assessment for Nuclear Power Plants was published in 2010 and revised after Fukushima-Daiichi nuclear accident. The DPP of DS528 (concerning the review of the safety guide SSG-4) was prepared in January 2020 and approved by NUSSC in June 2020. The DS528 was aimed at a full revision of the current version of the safety guide SSG-4 to: ensure coherency and consistency with relevant IAEA Safety Standards, e.g. GSR Part 4 (Rev. 1) Safety Assessment for Facilities and Activities (2016) SSR-2/1 (Rev. 1) Safety of Nuclear Power Plants: Design (2016) SSR-2/2 (Rev. 2) Safety of Nuclear Power Plants: Commissioning and Operation (2016) SSG-3 (under partial review, DS523) Development and Application of Level 1 PSA for Nuclear Power Plants incorporate experience gained through IAEA TSR-PSA peer reviews feedback from Fukushima-Daiichi nuclear accident recent developments in Member States in specific areas related to PSA

Status of the Document Steps of preparation of the document STEP 1: Preparing a DPP STEP 2: Approval of DPP by the Coordination Committee STEP 3: Approval of DPP by the relevant review Committees STEP 4: Approval of DPP by the CSS STEP 5: Preparing the draft STEP 6: Approval of draft by the Coordination Committee STEP 7: Approval by the relevant review Committees for submission to Member States for comments STEP 8: Soliciting comments by Member States STEP 9: Addressing comments by Member States STEP 10: Approval of the revised draft by the Coordination Committee Review in NSOC-SGDS (Technical Editorial review) STEP 11: Approval by the relevant review Committees STEP 12: - Submission to the CSS - Submission in parallel and approval by the Publications Committee - MTCD Editing - Endorsement of the edited version by the CSS STEP 13: Establishment by the Publications Committee and/or Board of Governors (for SF and SR only)) STEP 14: Target publication date Status / Planned date DONE (March 2020) DONE (April 2020) June 2020 November 2020 2Q 2021 4Q 2022 2Q 2023 2Q 2023 4Q 2023 1Q 2024 2Q 2024 4Q 2024 1Q 2025 3Q 2025 4

Meetings Drafting process (4 CS): 27-30 July 2020 - To define table of contents and scope, including NUSSC confirming the resolution of NUSSC Members (virtual meeting); 9-12 March 2021 - Discussion of table of contents and scope of each chapter (virtual meeting); 14-17 September 2021 Discussion and review of the first draft (hybrid meeting); 7-10 December 2021 Review and finalization of the draft (virtual meeting). Independent review (1 CS): 25-27 October 2022 Discussion of comments of independent review of the draft (hybrid meeting). Revision / resolution of comments from Member States & NUSSC Members (2CS): 30 May 2 June 2023 Revision of NUSSC Members' comments on the draft (hybrid meeting); 15 19 January 2024 Revision of Members States comments on the draft (hybrid meeting);

Overview of the Document The scope of the revised version has been expanded to address the necessary technical features of Level 2 PSA and applications providing a technology inclusive methodology applicable to water cooled and non-water cooled reactors. More detailed guidance on several topics such as: Definition of Level 2 PSA criteria or objectives; Definition and grouping the plant damage states; Development of the accident progression event trees; Performing containment integrity analyses; Integration of strategies for dealing with the progression of core damage; Modelling the use of non-permanent equipment; Human and equipment reliability analyses; Multi-unit considerations; The Spent Fuel Pools inside and outside of the reactor containment building.

DS528 Outline (1/2) 1. INTRODUCTION 2. GENERAL CONSIDERATIONS RELATING TO THE PERFORMANCE AND USE OF LEVEL 2 PSA 3. PROJECT MANAGEMENT AND ORGANIZATION FOR PSA 4. FAMILIARIZATION WITH THE PLANT DESIGN AND SEVERE ACCIDENT MANAGEMENT 5. INTERFACE WITH LEVEL 1 PSA: GROUPING OF SEQUENCES 6. SEVERE ACCIDENT PROGRESSION ANALYSIS 7. CONTAINMENT INTEGRITY ANALYSIS 8. HUMAN AND EQUIPMENT RELIABILITY ASSESSMENT 9. SOURCE TERMS FOR SEVERE ACCIDENTS 10. DEVELOPMENT OF ACCIDENT PROGRESSION EVENT TREE OR CONTAINMENT EVENT TREE AND QUANTIFICATION OF EVENTS 11. QUANTIFICATION OF EVENT TREES AND ANALYSIS OF RESULTS 12. DOCUMENTATION OF THE ANALYSIS: PRESENTATION AND INTERPRETATION OF RESULTS

DS528 Outline (2/2) 13. SPENT FUEL POOL 14. MULTI UNIT LEVEL 2 PSA 15. USE AND APPLICATIONS OF THE PSA REFERENCES APPENDIX OVERVIEW OF HUMAN RELIABILITY ANALYSIS IN A LEVEL 2 PSA DEFINITIONS ANNEX I COMPUTER CODES FOR SIMULATION OF SEVERE ACCIDENTS ANNEX IISAMPLE OUTLINE OF DOCUMENTATION FOR A LEVEL 2 PSA STUDY ANNEX IIIEXAMPLES OF COMMON RISK METRICS IN LEVEL 2 PROBABILISTIC SAFETY ASSESSMENT CONTRIBUTORS TO DRAFTING AND REVIEW

Member States comments: Comments by Member States (Total 404) 6 UK USA 4 1 Senegal 84 Saudi Arabia 8 Russian Federation 9 Pakistan 2 Mexico 19 Japan 10 Israel 13 Hungary 76 Germany 10 France 29 Finland 23 ENISS 30 China 15 Canada 65 Bulgaria 0 10 20 30 40 50 60 70 80 90 9

Member States comments: Comments by resolution (total 404) 250 225 200 150 116 100 63 50 0 Accepted Accepted with modifications Rejected 10

Examples of comments accepted Several editorial modifications; Request to define the term of safety systems ; Recommendations related to the scope of Level 2 PSA; Improvements of text for clarify regarding tables of attributes of PDS, information required for plant familiarization, uncertainties, spent fuel pool, multi-unit Level 2 PSA; Text in paras 12.1 to 12.3 deleted to avoid repetition with paras in DS523; Improvements of risk metrics definitions in Annex III table for several Member States. 11

Examples of comments not accepted Specifying recommendations for non-water cooled reactors; Deleting description of approaches: integrated or separated; Role of Level 1 PSA for the practical elimination concept; Adding specific recommendations for spent fuel pool, numerical goals for multi-unit Level 2 PSA, example of fragility curve / surface; Identifying dominant sources of uncertainties for the uncertainty analyses. 12

NUSSC Member comments: Comments by NUSSC Members (Total 107) 4 USA 5 Ukraine 4 Japan 9 Iran 16 India 56 Germany 1 ENISS 5 Canada 7 Brazil 0 10 20 30 40 50 60 13

NUSSC Member comments: Comments by resolution (Total 107) 40 40 37 35 30 30 25 20 15 10 5 0 Accepted Accepted with modifications Rejected 14

Examples of comments accepted Text improvements, text additions and references; Role of Level 2 PSA for demonstration of practical elimination; Equipment reliability for equipment credited in Level 2 PSA; Corrections concerning radionuclides in source term groups; Footnote 33 moved to the main text concerning the interpretation of reactor modules in SMRs regarding multi-units PSA; Consistency with SSG-3 (Rev.1) concerning risk informed decision-making; Advice on interpretation of Tables III-1 and Table III-2 concerning Member States values and definitions of large release frequency and large early release frequency. 15

Examples of comments not accepted Further details on computer codes for Level 2 PSA; Further examples on non light water reactor technologies; Editorial changes that will be addressed by the professional editors at Step 12; Terminology inconsistent with other IAEA standards; Deleting sections on project management and familiarization with the plant design; Adding a picture related to integrated approach; Text modification on human reliability analysis. 16

NUSSC Member Comments: Summary All comments were addressed, and resolutions were discussed with the NUSSC Members There are no unresolved comments