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:
d in anticipation of the need for additional time for corrective maintenance, an assessment of transition risk (the risk of transitioning from power operation to the mode required by the current TS in question) that could be incurred under the current, shorter CT may be desirable if the initial calculated risk increase is near or somewhat above the acceptance guidelines. In addition, TS changes to requirements for a controlled shutdown (i.e., the time allocated to transit through hot standby to hot shutdown to cold shutdown or to the final state that should be reached) should be evaluated using a model for the transition risk covering these periods or at least a qualitative evaluation of the transition risk, if possible. 2.3.3 Probabilistic Risk Assessment Modeling and Level of Detail 2.3.3.1 Detail Needed for Technical Specification Changes To evaluate a TS change, the PRA should model specific systems or components involved in the change. The model should also be able to treat the alignments of components during periods when testing and maintenance are being carried out. Typically, limiting conditions for operations (LCOs) and surveillance requirements relate to the system trains or components that are modeled in the system fault trees of a PRA. System fault trees should be sufficiently detailed to specifically include all the components for which surveillance tests and maintenance are performed and are to be evaluated. Additional detail that should be incorporated in the PRA in support of TS changes includes the following: a. For CT evaluations, system train-level models are adequate if all components belonging to the train are clearly identified (i.e., all those components that could cause the train to fail). b. For evaluating SFs, individual component-level models are necessary. c. Since PRAs typically model the plant at the individual component level, they may be used directly to analyze both CTs and SFs. d. Component unavailability models should include