Document: NRC Regulatory Guide
Document ID: 2459a562-8984-421c-8058-d096dbb9617c
Document Type: regulatory_guide
Title: Guidelines for Categorizing Structures, Systems, and Components in Nuclear Power Plants According to Their Safety Significance
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0314/ML031430373.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.201
CFR Part: 
CFR Title: 

Content:
nd corrective action program, or other aspects of treatment, would be effective in sufficiently minimizing CCF potential such that the sensitivity studies remain bounding. In summary, if this approach is adopted, the determination of the appropriate factor (or factors) to use in the risk sensitivity study must be determined in concert with the consideration of planned changes in treatment. As part of this evaluation, the NRC expects licensees to: (a) demonstrate an understanding of common cause effects and degradation mechanisms and their potential impact on RISC-3 SSCs; (b) demonstrate an understanding of the programmatic activities that provide defenses against CCFs and failures resulting from degradation; and (c) to factor this knowledge into both the treatment applied to and the reliability assumptions made for the RISC-3 SSCs. An alternative approach is to set the increase in unreliability at such a level that the increase would be detected through the corrective action and feedback processes. When this approach is used, the licensee must develop, document, and submit a quantitative evaluation based on the current unreliability of the SSCs, the number of SSCs, the frequency of the opportunities to identify failures, and the monitoring and corrective action program that will identify the minimum increase in failure rates that can be detected through monitoring and the corrective action program. When non-PRA studies are used to address certain risk contributors (e.g., seismic initiators or fires) this approach is not directly applicable. In this case, it is necessary for the licensee to provide an argument as to why the impact on CDF and LERF from adopting the non-PRA approach is not significant. 19. Section 9 Under the sub-heading “Review of Safety Significant Functions”, it is stated “SSCs which have high failure probabilities (usually indicative of screening values) and meet the screening criteria solely on the basis of Fussell-Vesely importance may have