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:
redundant set that can be justifiably identified as a common cause failure group. (viii) The SSC is a part of a system that acts as a barrier to fission product release during severe accidents. It is expected that a sufficiently robust categorization process would result in fission product barriers (e.g., the containment shell or liner) being categorized as safety significant. (ix) The SSC is depended upon in the Emergency Operating Procedures or the Severe Accident Management Guidelines. (x) Failure of the SSC will result in unintentional releases of radioactive material in excess of 10 CFR Part 100 guidelines even in the absence of severe accident conditions. 13 (xi) The SSC is relied upon to control or to mitigate the consequences of transients and accidents. If none of the above eleven conditions is true, the IDP could use a qualitative evaluation process to determine the impact of relaxing requirements on SSC reliability and performance. This evaluation includes identifying the functions being supported by operation of the SSC, the relationship between the SSC’s failure modes and the functions being supported, the SSC failure modes for which the failure rate may increase, and the SSC failure modes for which detection could become or are more difficult. The IDP could then justify low safety significance of the SSC by demonstrating the following: 7. The reclassification is consistent with the defense-in-depth philosophy. 8. Operating experience indicates that active degradation mechanisms (e.g., for piping flow accelerated corrosion or microbiologically-induced corrosion) for passive and active SSCs are not present, relaxing the treatment requirements will have minimal impact on SSC performance and reliability, and degradation in the ability of the SSC to perform its safety functions will be detected in a timely fashion 9. Relaxing the requirements will have a minimal impact on the expected onsite occupational or offsite doses from transients and accidents