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:
is accidents; the exclusion of most instrumentation and reactor protection system equipment from the models; the exclusion of emergency preparedness and plant monitoring equipment from the models; the combining of SSCs with identical failure consequences into grouped basic events; and not including some highly reliable SSCs when other less reliable SSCs (of similar impact) or operator actions are modeled. Categorization of the safety significance of SSCs for utilization in GQA uses quantitative PRA results, supplemented by qualitative engineering evaluations to include SSCs not modeled in the PRA, to develop an initial categorization referred to in this regulatory guide as candidate high or low safety significance. These initial categories should be evaluated, modified as appropriate, and approved during a final traditional engineering decisionmaking process. Such a combined, integrated approach is necessary to utilize the strengths and avoid inherent limitations in both probabilistic and traditional engineering analysis methodologies. 2.1 Safety-Significance Categorization A minimum of two levels of categorization should be utilized, preferably labeled high and low safety significant. At the prerogative of the licensee, a greater number of safety-significance levels can be defined, such as three levels composed of high, medium, and low safety significance. From a regulatory point of view, it is essential that high safety-significant items are not inappropriately categorized as less than high, since these might then be inappropriate candidates for reduced QA requirements. Therefore, for regulatory purposes, high safety significance may be assumed or assigned. Only assignments of low and medium safety significance must be justified. Systems have a variety of operating modes and perform a variety of functions, with each function a well-defined task requiring the proper operation of some subset of system equipment. Although certain QA controls are applied at the