Document: NUREG-0800
Document ID: b07c8dd1-23f6-41f1-a3ba-aa378f9ea59a
Document Type: srp
Title: RISK-INFORMED INSERVICE INSPECTION
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0325/ML032510135.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.9.8
CFR Part: 
CFR Title: 

Content:
ed industry codes. II.2.2.5 Consequences of Failure The impact on risk that is due to piping pressure boundary failure should consider both direct and indirect effects. Consideration of direct effects should include failures that cause initiating events or that disable single or multiple components, trains, or systems, or a combination of these effects. Indirect effects of pressure boundary failures that affect other systems, components, or piping segments, also referred to as spatial effects such as pipe whip, jet impingement, flooding, or consequential initiation of fire protection systems, should also be considered. 3.9.8-11 The direct and indirect effects of pipe failures should be characterized to incorporate appropriate failure mechanisms and dependencies into the PRA model. The possibility of different leak sizes ranging from minor leaks to full rupture should be considered. In general, the leak size resulting in the most severe consequence should be selected to characterize the consequence for each segment. An acceptable method of incorporating pipe failures is to classify pipe failures as leaks, disabling leaks, and breaks. Each of these failure modes may be characterized with a different failure probability or potential and a corresponding potential for degrading system performance through direct or indirect effects or both. The time available for operator actions also depends on the break size, and this timing dependence should be recognized and incorporated into the analysis as appropriate. II.2.2.6 Risk Impact of ISI Changes The guidelines discussed in Regulatory Guide 1.174, in Section 2.2.5, “Comparison of PRA Results with the Acceptance Guidelines,” are applicable to ISI change requests. General guidance for reviewing the risk impact from changes to the current licensing basis can be found in SRP Chapter 19 in Section III.2.2.5, “Evaluation of Risk Impact.” The methods used to determine the piping failure potential, the piping failure