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:
standby time-related and cyclic demand-related contribution) could be used to support development of the proposed RI-IST program. In this case, such a breakdown of the failure rate should be justified through data analysis or engineering analyses. This approach for evaluating test interval extensions assumes that failures are random occurrences and that the frequency of these occurrences does not increase as the test interval is increased (i.e., constant standby failure rate). This assumption is based on data from current IST test intervals, and therefore, may not include insidious effects that arise from extended test intervals (e.g., corrosion or erosion, intrusion of foreign material into working parts, adverse environmental exposure, or breakdown of lubrication) that could significantly degrade the component if test intervals become excessively long. Therefore, there is some concern that the standby failure rate may increase as test intervals are extended. Unless it can be demonstrated that either degradation is not expected to be significant or that the test would identify degradation before failures are likely to occur, use of the constant failure rate model could be nonconservative. One way to address this uncertainty is to use the PRA insights to help design an appropriate implementation and monitoring program; for example, to approach the interval increase in a stepwise fashion rather than going to the theoretically allowable maximum in a single step, or to stagger the testing RG 1.175, Page 17 of redundant components (test different trains on alternating schedules) so that the population of components is being sampled relatively frequently, even though individual members of the population are not. By using such approaches, the existence of the above effects can be detected, and compensatory measures taken, to correct the testing of the remaining population members. However, it is important that the monitoring includes enough tests to ensure that these