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
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CFR Title: 

Content:
on, but it must be supplemented by additional considerations during the integrated decisionmaking process. Regulatory positions for the required PRA quality and scope are further defined in Regulatory Guide 1.174. The PRA model should be developed to the component level for the systems important to safety. 6. Categorization of Components When using risk importance measures to identify components that are low risk contributors, the potential limitations of these measures have to be addressed. Therefore, information to be provided to the licensee's integrated decisionmaking process should include evaluations that demonstrate the sensitivity of the risk importance results to the important PRA modeling techniques, assumptions, and data. Issues that the licensee should consider and address when determining low risk 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, and recovery actions). 3.9.7-9 Rev. 0-August 1998 While the categorization process can be used to identify areas in which testing strategy can be improved and areas in which sufficient safety margins exist to the point that testing strategy can be relaxed, it is the determination of the change in risk from the overall changes in the IST program that will help determine acceptability of the RI-IST program. Therefore, there are no generically applicable acceptance guidelines for 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 the next section. Therefore, when categorizing components that are not modeled in the PRA, licensees must take into account the reasons