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:
han the current Figure 5-6. Thus, if a SSC participates in an unscreened scenario or is credited in the screening of the scenario, then that SSC would be considered safety-significant. 13. Section 5.5 NUMARC 91-06 is stated in NEI 00-04 as an attempt to ensure that the plant has an appropriate complement of systems available at all times. The NRC staff is not sure that the use of NUMARC 91-06, as described in NEI 00-04 and as implemented through the plant-specific Outage Risk Management Guidelines, will provide conservative categorization results. Therefore, as part of the licensee’s submittal requesting to implement 10 CFR 50.69, the licensee must demonstrate the adequacy of its approach to addressing shutdown risk for this 7 application and ensure that the approach will provide conservative results. If this approach is used, any (not just the primary) SSCs identified in the plant-specific Outage Risk Management Guideline must be considered safety-significant. Further, if a licensee wants to gain the full benefit from the proposed 10 CFR 50.69 in reducing treatment of SSCs, the licensee should consider performing a shutdown PRA, which would provide greater ability to identify SSCs that could potentially be categorized as LSS. 14. Section 6.1 The NRC staff agrees that when an SSC is determined to be LSS, it is appropriate to confirm that adequate defense-in-depth is preserved. However, it is not clear how Figure 6-1 is to be interpreted in this process. The NRC staff interpretation is that the figure is intended to address defense-in-depth at the critical safety function level (i.e., the figure should be used for each critical safety function and the top line identifies what system(s) is(are) available in addition to the system of which the SSC is a part). The row is to be chosen commensurate with the highest frequency initiating event for which failure of the critical safety function would lead to core damage or a large release. Further, in a risk-informed