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:
ed from the safety significance of individual SSCs. An explanation of the difference should be included in the training provided to the IDP. The staff notes that the safety significance of a CCF event that simultaneously fails nominally redundant trains in a system will generally provide a measure of system function safety significance consistent with SSC safety significance. Therefore, the RAW of CCF events must also be considered in this assessment. Because of the potential confusion between a system safety function (e.g., high pressure injection from the high pressure injection system) and the train-level system safety function (e.g., high pressure injection from one high pressure injection train) there are a number of guidelines within the report that are ambiguous. For example, the discussion of the IDP process in this section includes several questions based on whether the failure of the SSC will fail a “function.” Until the NEI 00-04 guidance is further clarified, the definition of “function” that results in the highest safety significance assignment for an SSC must be used. 17. Section 7.2 The second bullet on page 37 states that if the SSC is of low safety significance based on the internal events, but potentially high (ie.., safety-significant) because of external events, then the integral assessment should be relied on. This is too strong a statement. The NRC concludes that though the IDP may raise a candidate LSS SSC to safety-significant, the IDP cannot lower a safety-significant SSC to LSS. If a SSC is determined to be safety-significant 9 by any of the analyses supporting the risk-informed categorization process, including the appropriate sensitivity studies, then the SSC is safety-significant. Only through a thorough recategorization 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