Day 1 — Tuesday, February 4, 2003

Welcoming Remarks, Agenda Review, and General Information

Rob Tregoning of the USNRC began the meeting with a review of the agenda and general announcements. In addition, the individuals present were asked to introduce themselves with a short background of their experience related to the issue of LOCA frequency estimations.

Mike Mayfield of the USNRC welcomed the group and offered his perspective on the subject. Hossein Hamzehee of the USNRC also stressed the importance of the LOCA frequency determination for the continuing effort to explore risk-informed revision of 10 CFR 50.46, which govern ECCS requirements.

The meeting attendance list was provided to all of the meeting participants.

Presentation: Importance of LOCA Distributions to 50.46

The first presentation on the agenda was made by Alan Kuritzky of the USNRC. Alan laid out the importance of LOCA frequency estimates with respect to the 50.46 revision effort. Some of the key points from his presentation and subsequent discussion are outlined below:

• The NRC staff proposed a plan for risk-informing the technical requirements of 10 CFR Part 50 (Option 3) in SECY 99-264.

• Stakeholder input was considered in the recommendation to focus revision on the ECCS requirements.

• These requirements are covered in three regulations: 10 CFR 50.46, Appendix K to 10 CFR 50.46, and General Design Criterion (GDC) 35.

• Potential changes to 10 CFR 50.46 fall in one of the following areas

• ECCS reliability (one of the focuses of elicitation — due to the simultaneous Loss of Offsite Power [LOOP] requirement)

• ECCS acceptance criteria

• ECCS evaluation model

• ECCS LOCA size definition (another focus of the elicitation)

• The elicitation results will impact changes to the ECCS reliability areas and the ECCS LOCA size definition.

• ECCS reliability is primarily impacted because of the effort to eliminate the simultaneous LOCA — LOOP requirement. This has two pieces:

• LOCA initiation frequencies and

• Conditional probability of LOOP given a LOCA.

The focus of the current expert elicitation effort will be to obtain robust LOCA frequencies for use in the LOCA-LOOP evaluation. Interim LOCA frequencies were developed last spring as part of an internal

NRC elicitation effort and these have been used to demonstrate the technical feasibility of a change in this requirement. The results of this interim NRC effort will not be made available to this panel until after the wrap-up meeting to ensure that the panel results are independent. The objective is to have this project completed by December 2003. More detail on this topic is provided in Rob Tregoning’s subsequent presentation.

For the LOCA size definition effort, a computational code is being developed to incorporate LB LOCA contributions from pipe breaks and other component failures. The results of this panel will be used to normalize the analytical code results and also provide distributions for important input variables. The targeted completion date for this technical feasibility study is July 2004. More detail on this topic is also provided subsequently.

Rob Tregoning indicated that the LOCA frequencies would also be used within the 10 CFR 50.61 risk — informed revision effort (PTS Rule) to ensure that current calculations are acceptable.