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:
eet similar to that developed for the system-level results in Section 7. For SSCs not modeled explicitly in the PRA, the IDP could use the following guidance to determine if low safety significance is appropriate based on traditional engineering analyses and insights, operational experience, and information from licensing basis documents and design basis accident analyses. The IDP could assess the safety significance of these SSCs by determining if: (i) Failure of the SSC will significantly increase the frequency of an initiating event, including those initiating events originally screened out in the PRA. (ii) Failure of the SSC will compromise the integrity of the reactor coolant pressure boundary. It is expected that a sufficiently robust categorization process would result in the reactor coolant pressure boundary being categorized as RISC-1. (iii) Failure of the SSC will fail a safety-significant function, including SSCs that are assumed to be inherently reliable in the PRA (e.g., piping and tanks) and those that may not be explicitly modeled (e.g., room cooling systems, and instrumentation and control systems). For example, it is expected for pressurized water reactors (PWRs) that a sufficiently robust categorization process would categorize high energy ASME Section III Class 2 piping of the main steam and feedwater systems as RISC-1. (iv) The SSC supports important operator actions required to mitigate an accident, including the operator actions taken credit for in the PRA. (v) Failure of the SSC will result in failure of safety-significant SSCs (e.g., through spatial interactions or through functional reliance on another SSC). (vi) Failure of the SSC will impact the plant’s capability to reach and/or maintain safe shutdown conditions. (vii) The SSC is one of a 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