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:
ther for preventive or corrective maintenance). For appropriate configuration risk management and control, preventive and corrective maintenance activities need to be considered, and licensees should, therefore, have the ability to address the subtle difference that exists between maintenance activities (Section A-1.3.2 of Appendix A to this guide provides details). To account for the effects of test placements for redundant components in relation to each other (e.g., staggered or sequential test strategy), time-dependent models and additional evaluations with specialized codes may be used. If the PRA does not model the system for which the TS change is being requested, specialized analyses may be necessary to demonstrate the sufficiency of the proposal. Examples of these situations follow: a. When a system is modeled in the event tree, but a detailed fault tree model is not provided (direct estimate of system unavailability from experience data or expert judgment is used), the TS evaluation can proceed in several ways, such as for example: (1) A separate fault tree can be developed for the system for TS evaluation and used to complement the existing PRA model without directly modifying the PRA (e.g., detailed separate fault tree modeling of the reactor protection system combined with the existing PRA model). (2) A bounding evaluation can be conducted based on the impact of system failures that are modeled in the PRA event trees; that is, failure of any component in the system can be assumed to cause system failure. b. When a separate fault tree is developed, specific TS requirements within the system can be changed and changes in the system unavailability can be measured, which can then be used in the PRA model to obtain the corresponding risk measures, as appropriate. Such evaluations can be considered like those evaluations made directly using PRA models, but they should satisfy the following conditions: DG-1287, Page 14 (1) Failures within the system should not