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:
of failure. If the redundant component is successfully tested before taking the component down for PM, QC can then be equated to zero for a short-duration PM (i.e., when the duration of the PM is much less than the test interval). DG-1287, Appendix A, Page A-6 A-1.3.2.3 Conditional Core Damage Frequency When the Component Is Not Down for Maintenance or Is Tested Operable The conditional CDF is reduced when the component is not down for maintenance or when it has just successfully been tested. The calculation of CT and SF risk contributions involves calculating this conditional CDF (R0). For evaluating the CT risk contribution, R0 signifies that the component is not down for test or maintenance, and setting test and maintenance downtime unavailabilities to the “false,” or “F,” state represents this condition. In this example, QMA and QTA should be changed to the “F” state. For SF evaluations, R0 signifies that the component is up, which is known from the test and is represented by setting its unavailability to “false.” In this example, QLA, QMA, and QTA should be changed to the “F” state. In many cases, the reduction in CDF from the baseline CDF is negligible. A-1.3.2.4 Conditional Core Damage Frequency When Multiple Components Are Involved To calculate conditional CDFs (R1 and R0) when multiple components are involved, the corresponding terms relating to each of the components should be changed to the “T” or “F” state. For each component, the corresponding terms relating to random failures, CCFs, test downtimes, and maintenance downtimes should be converted, as discussed above. When all the components modeled by a common-cause term are failed, this term changes to the “T” state for calculating R1. Otherwise, it is modeled as discussed above, representing the unavailability of the remaining components. In many PRA computer codes, the CCF term does not retain the specific component designator (e.g., a unique notation identifying the