ML051020010
| ML051020010 | |
| Person / Time | |
|---|---|
| Issue date: | 04/22/2005 |
| From: | Dyer J Office of Nuclear Reactor Regulation |
| To: | Floyd S Nuclear Energy Institute |
| Thompson John W., NRR/DIPM/IIPB 415-1011 | |
| References | |
| Download: ML051020010 (4) | |
Text
April 22, 2005 Mr. Stephen D. Floyd Vice President, Regulatory Affairs Nuclear Generation Division Nuclear Energy Institute 1776 I Street, NW, Suite 400 Washington, D.C. 20006-3708
Dear Mr. Floyd:
As you know, the Nuclear Regulatory Commission (NRC) staff has been working with the Nuclear Energy Institute (NEI) and representatives of a number of reactor licensees, to define and implement a replacement performance indicator (PI) for the existing Safety System Unavailability (SSU) PI. The replacement PI is the Mitigating Systems Performance Index (MSPI). By letter dated September 15, 2004, the NRC committed to the implementation of MSPI.
MSPI is intended to be a risk-informed PI, relying on individual licensee probabilistic risk assessments (PRAs) for risk data to be used in the calculation of MSPI. Therefore a key step in the implementation process is to define a PRA quality standard that each licensee PRA must meet. In the fall of 2004, a MSPI PRA task group was formed, with both NRC and industry representatives knowledgeable in PRA being part of the group. The task group report on PRA quality was issued on December 16, 2004. The results of the task group were accepted by NEI, the licensee representatives, and by the NRC during a public meeting on MSPI in January 2005.
The industry set a goal of the first quarter of calendar year 2006 for MSPI implementation.
NEI has stated their intention to sponsor three industry workshops to aid licensees in preparations to implement MSPI. The first of these workshops was held in February 2005.
Following this workshop, at the March 2005 MSPI public meeting with the NRC staff, NEI announced that the industry could not carry out the activities defined in the task group report by the start of 2006. At the March 2005 MSPI public meeting, NEI proposed to change the PRA quality activities that need to be completed before implementation.
The NRC staff agrees that there may be alternative approaches to establishing the minimum level of PRA quality for MSPI, that accomplish the goal in a more efficient manner, thereby allowing MSPI to be implemented as originally scheduled. The NRC invites the industry to suggest alternative approaches. The staff acknowledges that one alternative from NEI was proposed verbally at the March 17, 2005, MSPI public meeting. That alternative proposal consisted of each licensee resolving the most important (A&B) facts & observations (F&Os) resulting from the industry peer reviews of PRAs, conducting a cross-comparison of licensee PRA results to identify and resolve outlier results, and adherence to the principles of Regulatory Guide (RG) 1.174 (in lieu of adherence to RG 1.200).
S. Floyd In describing this alternative approach in detail, the industry should address the following criteria:
(1) Define the process for identifying PRA model outlier Birnbaum importance measures, and address the following:
the criteria for grouping plants, define quantitative criteria for determining what is a potential outlier, the approach used to screen potential outliers based on legitimate differences arising from (a) plant differences, and (b) modeling differences such as appropriate credit for additional mitigating systems, assessing the impact of the A&B F&Os that are unresolved at the time of the cross-comparison.
(2) Provide a process for resolving outliers by, for example, including model revision and/or modification of the PRA model outputs (Birnbaum values) that are input to the MSPI program.
(3) Provide a timetable for resolving all A&B F&Os that affect MSPI, and finalizing the outlier identification.
However, consistent with the implementation process previously agreed to, for any alternative approach to be accepted by the NRC staff, the following criteria must also be met:
all industry activities to establish the minimum level of PRA quality must be completed by all licensees prior to MSPI implementation, and must allow time for NRC review, the alternative approach will not shift any significant burden to the NRC staff, the alternative approach will be considered by the joint NRC/industry MSPI PRA task group, and modified if necessary to ensure that the minimum level of PRA quality is established, the NRC/industry Reactor Oversight Process (ROP) working group will endorse the final PRA quality requirements and update the guidance documents accordingly.
The NRC staff goal with MSPI is that it be implemented successfully based on clear guidance and quality PRA data. Although the NRC staff is anxious to move forward with MSPI, the implementation goal of the beginning of 2006 should be a secondary consideration. As such, the timing of implementation should be revisited after the ROP working group has endorsed the industrys alternate approach. My staff plans to discuss this approach and criteria with industry at the next MSPI public meeting. Please contact John W. Thompson of my staff at (301) 415-1011 if you have any questions.
Sincerely,
/RA/
J. E. Dyer, Director Office of Nuclear Reactor Regulation
ML051020010 OFFICE DIPM/IIPB DIPM/IIPB/SC DIPM/IIPB/BC DIPM/D DSSA NRR/D NAME JThompson JAndersen SRichards BBoger SBlack JDyer DATE 04/13/05 04/14/05 04/15/05 04/15/05 04/21/05 04/22/05