Document: NRC Regulatory Guide
Document ID: c7a40fcc-fc9d-4eb2-ad86-f9f5b0f04c82
Document Type: regulatory_guide
Title: Plant-Specific, Risk-Informed Decisionmaking:  Technical Specifications (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1920/ML19206A489.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.177
CFR Part: 
CFR Title: 

Content:
ns that CT change evaluations should consider include the following: a. If CT risk evaluations are performed using only the PRA for power operation (i.e., to calculate the risk associated with (1) the equipment being unavailable during power operation for the duration of the CT and (2) any change in the CT), the risk associated with shutting the plant down because of exceeding the CT is not considered. In most cases, this risk has not been considered or, if considered, is assumed to further justify the requested change. If the risk evaluation results are marginal or exceed the guidelines for a proposed CT increase and the systems involve those needed for shutdown (e.g., residual heat removal systems, service water systems, auxiliary feedwater systems), the licensee may want to perform comparative risk evaluations of continued power operation versus plant shutdown to justify the proposed CT increase (Regulatory Position C.2.5 provides additional discussion on comparative risk evaluations). b. When calculating the risk impacts (i.e., a change in CDF or LERF caused by CT changes), the change in average CDF should be estimated using the mean outage times (or an appropriate surrogate) for the current and proposed CTs. If a licensee chooses to use the zero-maintenance state as the base case (i.e., the case in which no equipment is unavailable because of maintenance), the submittal should include an explanation stating so. Usually, data for outage times correspond to the current CT, not to the proposed CT. Different assumptions are made to estimate the outage time corresponding to the proposed CT. The submittal should discuss assumptions concerning changes in maintenance practices under the extended CT regime and characterize their impact on the results of the analysis. c. When the risk impact of a CT change is evaluated, the yearly risk impact that is calculated takes into account the outage frequency. A CT extension may imply that the maintenance of the component is