Document: NRC Regulatory Guide
Document ID: a5ee4c78-1135-4bb6-8d54-e974a3402f87
Document Type: regulatory_guide
Title: An Approach for Plant-Specific, Risk-Informed Decisionmaking: Graded Quality Assurance
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1221/ML12216A017.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.176
CFR Part: 
CFR Title: 

Content:
litative studies that have been developed. Evaluations based on quantitative external and shutdown studies may also be used. If importance measures from quantitative studies are combined with measures generated from internal event analyses, the licensee should ensure that the greater uncertainties inherent in the analysis of external events and the modeling of shutdown events are fully considered during the final categorization. 2.1.1 Identification of System Functions Definition of the proposed change includes identification of all the functions a system must perform. Although many system functions may eventually be categorized as low safety significant, characterization of the proposed change begins with a description of all functions a system must fulfill. System functions should include functions used during normal operation as well as all functions related to the prevention or mitigation of core damage, protection of containment integrity, or reduction in the release probability or consequence to the public from accidents and transients both within and beyond the design basis (e.g., risk analysis). 2.1.2 System Function Safety-Significance Categorization Determination of the safety significance of system functions is inherently a "top down" process, starting with the front-line systems and system functions directly involved in plant-level safety functions (such as reactivity control, reactor pressure control, and decay heat removal). The delivery of high-pressure primary coolant from the reactor water storage tank to the core may be categorized as a high safety-significant function. The pumps, valves, and other SSCs whose proper operation is required to fulfill this function derive their initial categorization from the significance of the function. Therefore, any determination of an SSC's safety significance requires determination of the safety significance of all functions the SSC supports. Similarly, determination of the safety significance of support system