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:
specific evaluations should be presented. In many cases, because of limited experience, the use of plant-specific data may result in very optimistic values justifying the use of generic data. DG-1287, Appendix A, Page A-8 A-2.3 Specific Data Needs Basic data needed for a TS change evaluation (using PRA information) for risk-informed regulation are those collected as part of the PRA. Comparative risk calculations for LCO changes require no additional data beyond those in the full-power operations Level 1 and the low-power/shutdown Level 1 PRAs. The following sections discuss additional data needs for evaluating changes in TS requirements, such as SFs and CTs. A-2.3.1 Maintenance Downtime Data Maintenance downtime data should be partitioned into plant-specific unplanned unavailability for unscheduled maintenance and planned unavailability for PM or testing. For this purpose, data are needed on the frequency of events leading to planned and unplanned maintenance (i.e., the number of occurrences of each type of downtime event during a given time period) and the time interval for each occasion the component was out of service. These data are also needed for judging whether an adequate CT is being provided to complete a repair. The distribution of downtimes also can be used to estimate the expected risk for a given CT. The distribution of time for unscheduled maintenance may shift with a change in a CT. For this reason, information about such an influence on the distribution is not expected to be available when the CT change is being evaluated. The average downtime can be assumed to proportionally increase with the increase in the proposed CT for downtimes associated with unscheduled maintenance. For scheduled (preventive) maintenance, the downtime assumed can be representative of plant practices (e.g., one-half of the CT). A-2.3.2 Maintenance Schedules and Frequency Maintenance schedule and frequency data include the maintenance scheduling used by the plant for defining