Document: NRC Regulatory Guide
Document ID: 6f84e3bf-9ff3-49fb-a16a-0de3b89e6bc6
Document Type: regulatory_guide
Title: An Approach for Plant-Specific Risk-Informed Decisionmaking for Inservice Inspection of Piping (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2103/ML21036A105.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.178
CFR Part: 
CFR Title: 

Content:
ed solely on plant-specific data. For common-cause failures, data from generic sources may be required. 2.2.1.2 Human Reliability Analyses to Isolate Piping Breaks For ISI-specific analyses, the human reliability analysis methodology used in the PRA should account for the impact that the piping segment break would have on the operator’s ability to respond to the event. In addition, the reliability of the inspection program (including both operator and equipment qualification), which factors into the probability of detection, should also be addressed. 2.2.2 Use of Probabilistic Risk Assessment for Categorizing Piping Segments When the impact of each segment’s failure on plant risk metrics has been determined, the safety significance of the segments is developed. The method of categorizing a piping segment can vary. For example, if the pipe failure event frequency or probability is estimated and the events are incorporated into the PRA logic model, importance measure calculations and the determination of safety significance, as discussed in RG 1.174 and SRP Chapter 19, “Severe Accidents,” may be performed. Alternatively, if a conditional CDF, conditional LERF, conditional core damage probability, or conditional large early release probability (depending on the impact the segment failure has on the plant) is estimated for each segment from the PRA, a CDF or LERF (or both) caused only by pipe failures may be developed by combining the conditional consequences and segment failure probabilities or frequencies external to the PRA logic model. Importance measures can also be developed using these results and these measures compared to appropriate threshold criteria to support the determination of the safety significance of each segment. The calculations used in such a process should yield well-defined estimates of CDF, LERF, and importance measures. The licensee should discuss and justify the threshold criteria used. As discussed in Section C.2.2.1, the consequence