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:
rom special treatment requirements in sufficient detail for the staff to endorse. Therefore, the endorsement of NEI 00-04 does not adopt any method to categorize the safety significance of the passive pressure boundary of SSCs. Until such a methodology is endorsed by the NRC, to support the categorization of SSCs, the licensee is required to describe in their plant-specific submittal requesting to implement 10 CFR 50.69, their methodology for addressing the passive pressure boundary of SSCs. NEI 00-04 defines relevant failure modes as “... those that are expected to be affected by the special treatment requirements being evaluated.” As it cannot be determined precisely what specific failure modes might or might not be impacted due to the reduction in the applicable special treatment requirements for low safety-significant SSCs, the licensee must consider all the 6 failure modes for the SSC identified in the PRA in making its Fussell-Vesely importance determination. This is consistent with the example provided in Table 5-1. The intent and implications of the discussion of using the component failure mode or dominant failure mode in the identification of safety-significant attributes is ambiguous and open to multiple interpretations. The NRC staff expects NEI to clarify how the safety-significant attributes may be used by licensees within the scope of 10 CFR 50.69. NEI 00-04 states that SSCs that have high failure probabilities are usually indicative of screening values. However, high failure probabilities can also be due to a number of other factors, including a lack of any testing of the SSC or an actually poor performing SSC. The NRC concludes that categorization results must not be overturned for SSCs simply because they have a high failure probability in the PRA, but rather, the licensee should first examine and determine the cause of the high value and then revise the model, as necessary. 10. Section 5.2 It is the NRC staff’s interpretation of the