Document: NUREG-0800
Document ID: ac43f632-9db1-4857-9f56-bfba45965456
Document Type: srp
Title: * These are modifications to a plant’s design, operations, or other activities that require NRC approval. These modifica
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0232/ML023250195.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19
CFR Part: 
CFR Title: 

Content:
tion as low safety significance, the licensee considered the defense-in-depth philosophy and available safety margins. Section III.2.1 of this SRP chapter presents review guidance on these topics. For SSCs not modeled in the PRA, reviewers should verify that the licensee’s process determined that the following conditions apply for each SSC that has been proposed as a candidate for relaxation or removal of current requirements: • The SSC does not perform a safety function, or does not perform a support function to a safety function, or does not complement a safety function. • The SSC does not support operator actions credited in PRAs for either procedural or recovery actions. • The failure of the SSC will not result in the eventual occurrence of a PRA initiating event. • The SSC is not a part of a system that acts as a barrier to fission product release during severe accidents. SRP 19-C7 • The failure of the SSC will not result in unintentional releases of radioactive material even in the absence of severe accident conditions. If any of the above conditions apply, or if SSC performance is difficult to quantify, the licensee should have used a qualitative evaluation process to determine the impact of relaxing requirements on equipment reliability and performance. This evaluation should include identifying those failure modes for which the failure rate may increase, and those for which detection could become more difficult. Reviewers should then verify that the licensee provided one or more of the following (or similar) justifications: • A qualitative discussion on how the change is consistent with the defense-in-depth philosophy and how the change maintains sufficient safety margins, • A qualitative discussion and historical evidence why these failure modes may be unlikely to occur, • A qualitative engineering discussion on how such failure modes could be detected in a timely fashion, • A discussion on what other requirements may be useful to