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:
t shutdown. Such companions can be used to decide which option is preferable and which alternatives may be used. Such evaluations particularly apply to systems used to remove decay heat. The following considerations apply in calculating transition risk: a. Various stages of the shutdown cooling phases and the operator’s interactions should be modeled to assess the impact on the CDF of shutting down the plant in an LCO. DG-1287, Appendix A, Page A-7 b. Any initiating event not modeled in the basic PRA but important during the shutdown phases should be modeled. Specific examples are those events that challenge the residual heat removal (RHR) system and that can render part of it unavailable. Additionally, the frequency of initiating events during the transition to shutdown may have to be reassessed since it may differ from that during power operation (e.g., more frequent loss of offsite power or loss of main feedwater during the transition to shutdown). c. Different recovery paths applicable at various stages of shutdown should be modeled to realistically quantify the risk of shutting down, considering the diminishing levels of decay heat. d. Available time margins for uncovering the reactor core and heating up the suppression pool (in a boiling-water reactor) or drying out the steam generator (in a pressurized-water reactor) should be modeled to evaluate specific accident sequences. A-2 Data Needs for Technical Specification Change Evaluations A request for plant-specific TS changes should use plant-specific data and not rely solely on generic data or data from similar plant designs. Usually, TS changes are requested because plant operation indicates that such changes are needed and, accordingly, plant-specific data are expected to be available. For the components or systems for which TS changes are being considered, plant-specific data should be evaluated, and assurance should be obtained that the data used are consistent with the plant experience. The use of