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:
n effort, which would involve going through the entire process and considerations at the same level of rigor and depth as the original categorization, can a SSC be recategorized lower than its initial categorization. The third bullet states that “if the SSC was found to be safety significant based on sensitivity studies, this should be communicated to the IDP, along with the base and integral significance for each hazard”. The SSCs must be categorized according to the highest safety-significance determined in the categorization process, including these sensitivity studies and the results of any other pertinent considerations (e.g., defense-in-depth, shutdown risks, etc.). The NRC staff notes that Figure 7-1 is overly simplistic and does not convey the proper level of detailed narrative expected in the documentation of categorization of SSCs. The NRC staff encourages the final version of NEI 00-04 to contain a more detailed and comprehensive example of the risk-informed SSC assessment worksheet. 18. Section 8 The final step in the allocation of SSCs into the different RISC categories is to show that the reduction in treatment of RISC-3 SSCs will not result in a significant increase in risk. This is done by performing the risk sensitivity study based on increasing the failure probabilities of those SSCs for which treatment is to be relaxed. This risk sensitivity study is a very important part of the categorization process. The choice of the factor to use to increase the failure probabilities of RISC-3 components must be based either on some reasonable expectation that it is bounding or that it is such that the change in unreliability it represents will be detected by the monitoring and corrective action program. To develop a reasonable bounding estimate of the increase in failure probability, the licensee would need to assess the impact that a change in treatment as a result of removal of special treatment requirements might have on the reliability of SSCs. The