Document: NRC Regulatory Guide
Document ID: 47b09be1-4bf8-45f9-a099-7fed871c09bd
Document Type: regulatory_guide
Title: Plant-Specific, Risk-Informed Decisionmaking: Inservice Testing (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2114/ML21140A055.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.175
CFR Part: 
CFR Title: 

Content:
sk contributors include truncation limit used, different risk metrics (i.e., CDF and LERF), different component failure modes, different maintenance states and plant configurations, multiple component considerations, defense-in-depth, and analysis of uncertainties (including sensitivity studies to component data uncertainties, common-cause failures (CCFs), and recovery actions). RG 1.174 and NUREG-1855 provide additional guidance on the treatment and analysis of uncertainties. While the categorization process can be used to highlight areas in which the testing strategy can be improved and areas in which sufficient safety margins exist to the point that the testing strategy can be relaxed, it is the determination of the change in risk from the overall changes associated with the RI-IST program that is of concern in demonstrating that Principle 4 has been met. Therefore, this RG in general does not provide the threshold values of importance measures used to categorize components as HSSC or LSSC. Instead, the licensee should demonstrate that the overall impact of the change on plant risk is small, as discussed in Regulatory Position C.2.2.3.3. As part of the categorization process, licensees should also address the initiating events and plant operating modes missing from the PRA evaluation. The licensee can do this either by providing qualitative arguments that the proposed change to the proposed RI-IST program will not result in an increase on risk, or by demonstrating that the component’s significant to risk in these missing contributors are maintained as HSSC. 2.2.3.3 Use of a Probabilistic Risk Assessment to Evaluate the Risk Increase from Changes in the Inservice Testing Program One of the important uses of the PRA is to evaluate the impact of the proposed RI-IST program with respect to the changes in CDF and LERF, as discussed in Sections C.2.4 and C.2.5 of RG 1.174. In addition, the PRA can provide a baseline risk profile of the plant, and the extent of