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:
guidance for categorizing SSCs in accordance with their safety significance using the process described in Draft Revision C of Nuclear Energy Institute (NEI) 00-04, “10 CFR 50.69 SSC Categorization Guideline.” (ADAMS Accession No. ML021910534). The categorization process determines the safety significance of SSCs and places them into one of four risk-informed safety class (RISC) categories. The safety significance of SSCs is determined by an integrated decision-making process, which incorporates both risk and traditional engineering insights. The safety functions of SSCs include both the design basis functions (deriving from the safety-related definition) and functions credited for severe accidents. Treatment requirements are then commensurately applied for the categorized SSCs to maintain their functionality and reliability. Figure 1 provides a conceptual understanding of the new risk-informed SSC categorization scheme. The figure depicts the current safety-related versus non-safety-related SSC categorization scheme with an overlay of the new safety-significance categorization. In the traditional deterministic approach, SSCs were generally categorized as either “safety-related” (as defined in 10 CFR 50.2) or non-safety-related. This division is shown by the vertical line in Figure 1. Risk insights, including consideration of severe accidents, can be used to identify SSCs as being either safety-significant or low safety-significant (shown by the horizontal line). This results in SSCs being grouped into one of four categories as represented by the four boxes in Figure 1. RISC-1 SSCs are safety-related SSCs that perform safety-significant functions. RISC-2 SSCs are non-safety-related SSCs that perform safety-significant functions. RISC-3 SSCs are safety-related SSCs that perform low safety-significant functions. Finally, RISC-4 SSCs are non-safety-related SSCs that perform low safety-significant functions. The proposed amendment to 10 CFR 50.69 defines