Barry Kaufer, Deputy Head, Regulation Nuclear Safety Division Le Seine St.-Germain

1. International WorkshopOnLevel 2 PSA and Severe Accident ManagementHosted by: Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbh, Köln, Germany29th to the 31st of March 2004 Barry Kaufer, Deputy Head, Regulation Nuclear Safety Division Le Seine St.-Germain 12, boulevard des Iles 92130 Issy-les-Moulineaux, France (barry.kaufer@oecd.org)

2. Table of contents • Safety and Regulation at OECD/NEA • Committee on the Safety of Nuclear Installations (CSNI) • Working Group on Risk Assessment (WGRisk) – Level 2 PSA • 1997 State-of-the-Art Report • 2004 Programme of Work • Summary

5. WGRisk • Over the past 24 years, PWG5 and now WGRisk have looked at the technology and methods used for identifying contributors to risk and assessing their importance. Work during the early part of this period was concentrated on Level 1 PSA methodology, but in recent years, the focus has shifted into specific PSA methodologies modelling issues and risk informed applications. During this long period WGRisk has produced over 40 technical reports, held over 25 international workshops and has issued several important consensus statements and opinion papers on specific aspects of PSA. • The main mission of the Working Group on Risk Assessment (WGRisk) is to advance the understanding and utilisation of Probabilistic Safety Assessment (PSA) in ensuring continued safety of nuclear installations and in improving the effectiveness of regulatory practices in Member countries. In pursuing this goal, the Working Group shall recognise the different methodologies for identifying contributors to risk and assessing their importance. While the Working Group shall continue to focus on the more mature PSA methodologies for Level 1, Level 2, internal, external, shutdown, etc. It shall also consider the applicability and maturity of PSA methods for considering evolving issues such as human reliability, software reliability, ageing issues, etc., as appropriate.

8. WGRisk – Level 2 PSA Discussion Outcomes • [1996] • In the early 1990’s, with the advent of increasing use of PSAs, a proposal was made at the 1993 PWG5 Annual meeting for future work in the area of Level 2 PSA. The main objective of the proposed task was to perform a state-of-the-art review of the methods available for performing level 2 PSAs and severe accident/source term uncertainty analyses for use in the regulatory process and the evaluation/implementation of severe accident management strategies. • [2002] • The reports from the experts and discussions within WGRisk show it is clear that if one were to use NUREG 1150 as a basis, experimental evidence over the past 10 years or more indicates that the perceptions of risk in Level 2 PSA has changed what may be considered significant. While it is not clear how the results would specifically change, the body of information that has been compiled would change the distributions that were used in NUREG 1150. Additionally, based on the national reports presented at WGRisk meetings many countries (Germany, Korea, Finland, France, Hungary, Czech Republic, Switzerland and Japan) are actively working on Level 2 PSA. Therefore the proposed workshop is considered is seen as beneficial to getting a better understanding of the current state-of-the-art.

9. WGRisk State-of-the-Art Report, 1997 • The report (Level 2 PSA Methodology and Severe Accident Management NEA/CSNI/R(1997)11) reviews and evaluates Level 2 PSA results and methodologies with respect to plant type specific and general insights • The report also looks at approaches and practices for using PSA results in the regulatory context and for supporting severe accident management programmes by input from Level 2 PSAs are examined. • The report is based on information contained in: • PSA procedure guides, PSA review guides and regulatory guides for the use of PSA results in risk-informed decision making, and • Plant specific PSAs and PSA related literature exemplifying specific procedures, methods analytical models, relevant input data and important results, use of computer codes and results of code calculations. The PSAs are evaluated with respect to results and insights. • Review of Report was performed in 2002 (next presentation)

10. Chapter 1 1. TASK DESCRIPTION AND WORKING METHODOLOGY • 1.1 Background • 1.2 Objective and Scope • 1.3 Level 2 PSA methodologies • 1.4 Accident management • 1.5 OECD/NEA activities on accident management • 1.6 OECD/NEA activities on severe accident phenomena • 1.7 Structure of the report.

11. Chapter 2 2 RESULTS AND INSIGHTS FROM RECENT LEVEL 2 PSA • 2.1 Examined PSAs and considered aspects • 2.2 Objectives and scope of recent level-2 PSAs. • 2.3 Plant characteristics influencing severe accident progression • 2.4 Level 2 methodology and codes • 2.5 Principal results, insights on containment failure modes and releases. • 2.6 References

12. Chapter 3 3 KEY SEVERE ACCIDENT ISSUES • 3.1 Key Severe Accident Phenomena. • 3.2 Review of severe accident computer codes • 3.3 Documentation of the Use of Severe Accident Computer Codes in Selected Level 2 PSAs for Nuclear

13. Chapter 4 • 4 SEVERE ACCIDENT MANAGEMENT • 4.1 Background and Objectives • 4.2 Evolution of an accident from the operators perspective • 4.3 Safety objectives for the development of SAM Guidance • 4.4 Examples of implemented provisions for mitigative SAM (level 2) and of their effectiveness • 4.5 Identification of Recovery and SAM Actions in the Level 1 Domain that can influence SAM in the Level 2 Domain. Some Examples • 4.6 References

14. Chapters 5 and 6 5 AVAILABLE METHODOLOGY FOR QUALITATIVE LEVEL 2 ANALYSIS • 5.1 Level 1/2 Interface • 5.2 Accident progression Event Trees • 5.3 Modelling of human intervention 6 EVALUATION OF LEVEL 2 PSA MODELS AND QUANTIFICATION • 6.1 Brief description of Methods • 6.2 Use of Expert Judgement • 6.3 Uncertainty Issue Quantification Technique

15. Chapter 7 • 7 INTEGRATED AND PSA INFORMED APPROACH TO DECISION MAKING • 7.1 Introduction • 7.2 Recent activities and publications related to risk informed decision making • 7.3 Quality requirements for PSAs • 7.4 National Positions on risk informed decision making. • 7.5 Treatment of Uncertainties • 7.6 Examples of risk informed decisions in the level 2 domain • 7.7 Conclusions

16. Appendices APPENDIX A: SEVERE ACCIDENT COMPUTER CODES • A.1 Fully Integrated Plant Simulation Codes • A.2 Separate Phenomena Codes • A.3 Parametric Codes APPENDIX B: • B.1 EVNTRE • B.2 SOLOMON • B.3 RISKMAN • B.4 SPSA

17. 2004 WGRisk Programme of Work (1) • International Workshop on Level 2 PSA and Severe Accident Management. • The main objectives are: • To provide a forum to discuss recent developments in the state-of-the-art of Level 2 PSA and Severe Accident Management. • The information gathered will be used to produce an addendum to the 1997 WGRisk report, • Will provide input into the joint workshop planned by WGAMA, IAGE and WGRisk on Evaluation of Uncertainties in relation to Severe Accident and Level 2 Probabilistic Safety Analysis (to be held in the Fall of 2004), and • Will be used to develop future tasks by WGRisk.

18. 2004 WGRisk Programme of Work (2) • The Use and Development of PSA in NEA Member Countries [NEA/CSNI/R(2002)18] • This report provides descriptions of the current status of PSA programmes in 17 Member countries including basic background information, guidelines, various PSA applications, major results in recent studies, PSA based plant modifications and research and development topics. While the compilation is a not complete compilation it provides a “snapshot” of the current situation in the Member countries and hence it provides reference information and various insights to both the PSA practicien and others involved in the nuclear industry. • The report forms the basis for a yearly round table discussion at WGRisk meetings and will be updated every 3 to 4 years.

19. 2004 WGRisk Programme of Work (3) • Use of PSA in Emergency Planning [Task 2004-3] • The aim is to identify the approaches being used in the member countries to define the emergency planning zones round nuclear facilities and how this relates to the information provided by the Level 2 PSA. The various approaches would be compared to identify similarities and differences. Consideration would also be given on whether it would be possible to define a common approach to using the Level 2 PSA information for this purpose.

20. 2004 WGRisk Programme of Work (4) • GAMA/WGRISK/IAGE Workshop on Evaluation of Uncertainties in Relation to Severe Accidents and Level 2 PSA • The objectives are: • To transfer information among Working Groups on an important cross-cutting issue. • To develop a coherent approach/understanding regarding uncertainties. • The product will be proceedings, and conclusions/recommendations addressed to CSNI and the Working Groups. • Tentative Date: Spring 2005

21. Summary • WGRisk State-of-the-Art report provided first in-depth look at Level 2 PSA Methodology in the Member Countries • WGRisk has an active programme in the area of Level 2 PSA and Severe Accident Management • WGRisk works (and will continue to work) with other working groups (e.g., GAMA) and other organisations (e.g., IAEA) to co-ordinate it work on this issue.