1. Adding value through knowledge © NNC Limited OECD_L2PSA_review/mla/dmj/02040.ppt OECD/NEA International Workshop on L2 PSA and SAM, 29 th -31 st March 2004, Koln A Review of OECD Report on Level 2 PSA and SAM Ming L Ang NNC Charles Shepherd NII

2. © NNC Limited OECD_L2PSA_review/mla/dmj/02040.ppt Level 2 PSA methodology (Chapters 5 & 6)  No major omission of methods for direct application or support role identified  Future revision on L2 methods may consider the following:  ROAAM methodology and case studies  case studies for L2 methods listed should be included (CET is exception)  critique of methods, e.g. current use of CET in the context of epistemic uncertainty  Approaches to ‘subjective judgement’, i.e. making normative expression in L2 PSAs, should be discussed  Review of CET case studies on uncertainty treatment and rationale  Discussion in most areas still biased towards NUREG- 1150 study, can benefit from more recent PSAs

3. © NNC Limited OECD_L2PSA_review/mla/dmj/02040.ppt Results and insights from recent Level 2 PSA (Chapter 2)  Discussion based on results applicable to PWRs and BWRs. Further examples of similar reactor designs may not be beneficial  Examples from other key groups of reactor designs should be considered, e.g. VVER, RBMK and advanced reactor

4. © NNC Limited OECD_L2PSA_review/mla/dmj/02040.ppt Severe accident phenomena and modelling (Chapter 3)  Description of SA phenomena well supported by a number of SOAR reviews (OECD, EC). Consideration should be given to include:  Phenomena relevant to shutdown, e.g. air ingression impact on accident progression and fp behaviour  Further discussion on uncertainty characterisation of phenomena based on more recent studies (e.g. EC STU project on significance of ST uncertainty)  No major omission of SA analysis codes identified. Consideration should be given to:  Update on modelling improvement, benchmark/validation of major integrated codes  Restrict Chapter 3 to current codes in use and major code activities (e.g. ASTEC, codes used for VVER and RBMK analysis)

5. © NNC Limited OECD_L2PSA_review/mla/dmj/02040.ppt Severe Accident Management (Chapter 4) and RI applications (Chapter 7)  No major omission of high level candidate strategies (both preventive and mitigative) identified  Update should reflect the significant international SAMG development and implementation programme (e.g. SAMIME review, COG SAMG development)  Discussion on probabilistic measure should be updated and included in Chapter 7 on RI applications  RI applications should be updated with recent studies and some discussion on the decision making process

6. © NNC Limited OECD_L2PSA_review/mla/dmj/02040.ppt Conclusions  Recent L2 PSAs have largely conformed to the approaches identified in the OECD report  Report can benefit with an update in most areas to reflect recent development  Current report does not cover SAM aspects on training and optimisation as defined in the study objective  Consideration should be given to include a discussion on source terms and L2/L3 interface  Revision as an addendum to report is recommended