Document: NUREG-0800
Document ID: 4e1d86bd-74a5-4678-8bc0-ffce3ba28ea0
Document Type: srp
Title: RISK-INFORMED INSERVICE TESTING
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0428/ML042880272.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.9.7
CFR Part: 
CFR Title: 

Content:
or these events. If the PRA results are adopted for other contributors, the reviewer should determine whether the same assumptions that apply for the PRA model are likely to apply under the conditions being addressed. For example, a 3.9.7-1 9 Rev. 0-August 1998 component categorized as LSSC based on results from a full-power PRA may not be a low risk contributor at shutdown conditions even if the component function and operating state is the same for both full-power and shutdown conditions. In this case, reduced redundancy in certain configurations may make a difference in the determination of risk importance. 7. Evaluating the Effect of Proposed Changes on Overall Plant Risk There are two major areas of review: the modeling of the impact of the change on individual components, and the propagation of these impacts through the PRA model for the calculation of plant risk. Modeling of the Effects of IST on PRA Basic Events The review procedure for the modeling of the effects of IST changes on individual components involves the following steps: * Identify the assumptions underlying, and the characteristics of the model used to evaluate the risk significance of extending selected component test intervals. * Establish whether the validity of the model depends on the efficacy of the tests to be performed as part of the IST program. * If the model does not address degradation, review the arguments why degradation is not a significant effect, If the model requires the estimation of an exposure time, the reviewers should establish that the fault exposure time credited in the PRA is reasonable in light of the IST interval and other activities. In general, the mean fault exposure time will be taken to be one half of the test interval. Some analyses may apply a fault exposure time other than this: a different fault exposure time for a given component might be claimed as a result of credit taken for non-IST validation of the performance of the component, perhaps by virtue of