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:
e. An important factor to ensure that defense-in- depth and safety margin considerations are not degraded during the implementation of GQA is control of potential common mode failures. As discussed in Regulatory Position 2.1.2.1, groups of nominally identical SSCs, utilized in multiple systems throughout the plant, can as an aggregate have high safety significance. Principle 4 in Regulatory Guide 1.174 (Ref. 3) states that any proposed increase in CDF and risk are small and are consistent with the intent of the Commission's Policy Statement (Ref. 1). Although the risk impact of GQA changes on individual components is expected to be minimal, reduced QA oversight may be applied to a large number of SSCs. It is recognized that limited data are available to define the impact of QA programs on SSC reliability. Accordingly, the licensee should perform a bounding analysis in which the failure rates or probabilities for basic events representing SSCs that may be subjected to reduced QA controls are set at some increased level (chosen and justified by the licensee). Alternatively, the licensee may choose to address the bounding analyses by modifying the uncertainty distributions in some manner (also chosen and justified by the licensee). The bounding analysis should include all SSCs modeled in the PRA on which QA controls may be 1.176-12 reduced in all systems that the licensee defines as being within the scope of the GQA program. SSCs not modeled in the PRA must be reviewed to verify that their failure will not impact any functions modeled in the PRA. Any potential impact on systems modeled in the PRA must be qualitatively addressed. It is recognized that the categorization of SSCs for the bounding analysis will necessarily be an initial categorization, most likely based on an evaluation of basic event importance measures augmented by a limited deterministic review. The purpose of such a study is not to estimate a new plant CDF and LERF, but to understand the potential or