ML21316A000
| ML21316A000 | |
| Person / Time | |
|---|---|
| Issue date: | 12/02/2021 |
| From: | Raymond Furstenau Office of Nuclear Regulatory Research |
| To: | Matthew Sunseri Advisory Committee on Reactor Safeguards |
| Gonzalez, Michelle - 415 5661 | |
| References | |
| Download: ML21316A000 (4) | |
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December 2, 2021 MEMORANDUM TO: Matthew W. Sunseri, Chairman Advisory Committee on Reactor Safeguards Signed by Furstenau, Raymond FROM: Raymond V. Furstenau, Director on 12/02/21 Office of Nuclear Regulatory Research
SUBJECT:
STAFF RESPONSE TO ADVISORY COMMITTEE ON REACTOR SAFEGUARDS LETTER, DATED OCTOBER 26, 2021, IN REGARD TO THE REVIEW OF REGULATORY GUIDE 1.247, ACCEPTABILITY OF PROBABILISTIC RISK ASSESSMENT RESULTS FOR ADVANCED NON-LIGHT WATER REACTOR RISK-INFORMED ACTIVITIES The purpose of this memorandum is to provide the U.S. Nuclear Regulatory Commission (NRC) staff's response to the Advisory Committee on Reactor Safeguards (ACRS) letter dated October 26, 2021, (Agencywide Document Access and Management System (ADAMS)
Accession No. ML21288A018) regarding Regulatory Guide (RG) 1.247, Acceptability of Probabilistic Risk Assessment Results for Advanced Non-Light Water Reactor Risk-Informed Activities.
During the 689th meeting of the Advisory Committee on Reactor Safeguards, October 5 through October 7, 2021, ACRS reviewed RG 1.247 that endorses with clarifications and qualifications the Probabilistic Risk Assessment (PRA) Standard for Advanced Non-Light Water Reactors (Non-LWRs). In addition, the ACRS Subcommittee (SC) on Future Plant Design reviewed this matter, including the standard itself on September 20, 2021. In a letter dated October 26, 2021, the ACRS provided conclusions and recommendations on RG 1.247. The staff reviewed the conclusions and recommendations, and the staffs responses are described below:
Conclusion and Recommendation 1:
RG 1.247 should be issued for trial use.
NRC Staff Response 1:
The staff appreciates the feedback from the ACRS. As recommended by the ACRS, the staff anticipate issuing RG 1.247 for trial use in March 2022.
CONTACTS: Anders Gilbertson, RES/DRA/PRB (301) 415-1541 Michelle Gonzalez, RES/DRA/PRAB (301) 415-5661
M. Sunseri Conclusion and Recommendation 2:
Before a final version of RG 1.247 is issued the staff should consider the following suggested changes, in addition to including lessons learned during review of trial applications of the standard.
- a. Rephrase the Resolution column of Appendix A of RG 1.247, to show the clarifications and qualifications, as Interpretations of the standard that are acceptable to the NRC staff, rather than as changes to the text of the standard.
- b. Include guidance that the initial search for initiating events and scenarios should be done without preconceptions or using existing lists.
NRC Staff Response 2:
Regarding the first part of the second conclusion and recommendation, the staff considered the ACRS feedback and understands the ACRS concern about the approach used to endorse the standard. During the ACRS subcommittee meeting on September 20th, a member of the Joint Committee on Nuclear Risk Management (JCNRM) raised a concern stating that approach taken to endorse the standard appeared as if the NRCs intent in Appendix A of RG 1.247 was to rewrite the requirements for the standard. The staff will explain the intent for the endorsement in the text of trial use version of RG 1.247 and will finalize that version with the existing approach of endorsement. This approach has been used extensively in numerous applications of RG 1.200, Acceptability of Probabilistic Risk Assessment Results for Risk-Informed Activities, for operating light-water reactors (LWRs) for more than 15 years. In that time, the staff have received no feedback on this approach related to the endorsement in RG 1.200. The staff endorsement does not intend to provide a new interpretation of requirements in the Standard, as necessary interpretations are provided by the standards developing organization, nor to change the text of the Standard, as the American National Standards Institute published the final edition of the Standard in early 2021. The staff endorsement provides resolutions to identified issues on using an acceptable PRA to support a regulatory application. Based on the extensive experience with the RG 1.200 framework, the staff are confident in the current approach to writing the endorsements of requirements but will consider this recommendation during the trial use period.
Regarding the second part of the second conclusion and recommendation, the staff agrees and will revise the appropriate related guidance in RG 1.247 to emphasize that the initial search for initiating events and scenarios should be performed without preconceptions or presumptions of what the final result of such an effort should be. Accordingly, the staff plan to emphasize in RG 1.247 that such a search should be performed without being biased by existing lists of internal and external hazards, hazard groups, and initiating events and without presumption that such lists are in and of themselves complete and sufficient. Additionally, following prior ACRS feedback on this issue, the staff have since initiated efforts, which are still in progress, to develop more detailed guidance on how to conduct searches for initiating events in such a manner.
Before issuing the final version of RG 1.247, the staff will address and include lessons learned during the trial use period.
M. Sunseri NRC Staff Response to other comments:
The ACRS recommended that the NRC staff considered the use of the term credit or crediting, in the context of human actions, to avoid implying to some engineers who may not be familiar with PRAs that we should assume that the action occurs and is successful. The staff will consider this feedback during the trial use period of RG 1.247.
ML21316A000; Memo ML21316A000 OFFICE RES/DRA/PRAB RES/DRA RES MThaggard NAME MGonzalez MG RFurstenau RF CAraguas for CA DATE Dec 2, 2021 Nov 18, 2021 Dec 2, 2021