Document: NRC Regulatory Guide
Document ID: c7a40fcc-fc9d-4eb2-ad86-f9f5b0f04c82
Document Type: regulatory_guide
Title: Plant-Specific, Risk-Informed Decisionmaking:  Technical Specifications (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1920/ML19206A489.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.177
CFR Part: 
CFR Title: 

Content:
he total yearly contribution from all the CTs being considered. When the CTs do not interact (i.e., when the downed components are not in the same minimal cutset), the yearly CT risk contribution from several CTs is the sum of the individual yearly CT risk contributions. When the CTs do interact (i.e., when two or more of the downed components are in the same minimal cutset), interaction of the CT risk contributions should be considered. c. When calculating the test-limited risk for changes in multiple SFs, the total test-limited risk should be properly evaluated. Simple addition of individual test-limited risks will not provide the combined test-limited risk. In a simple addition, the total test-limited risk contribution is underestimated because the interacting terms are neglected. A-1.2.2 Total Impact of Multiple Changes When multiple changes are requested, the total collective risk impact from all the changes should be evaluated. For example, for a group of CT and SF changes, this includes the total impact of all the requested CT changes, SF changes, and CT and SF changes. If multiple changes are made, the impact of each change is assessed individually; as a check, the plant probabilistic risk assessment (PRA) should be used to quantify the total impact. A-1.3 Quantification of Risk Measures A-1.3.1 Alternative Ways of Calculating Technical Specification Change Risk Measures In calculating the measures discussed for evaluating TS changes, two specific risk levels should be quantified using PRA. Focusing on the CDF level, the risk levels are R1, the increased risk level (e.g., CDF) with the component assumed down or equivalent component unavailability set to “true,” and DG-1287, Appendix A, Page A-3 R0, the reduced CDF with the component assumed up; that is, the component unavailability is set to “false.” A-1.3.1.1 Using Probabilistic Risk Assessment to Obtain Completion Time, Preventive Maintenance, and Configuration Risk Contributions R1 can be