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:
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 specific component involved may not be part of the name of the CCF term), and the relevant term cannot directly be identified by searching the names of the input parameters of the PRA. The description of the CCF terms modeled in the PRA may need to be examined to identify the relevant term or the input parameter. A-1.3.3 Treatment of Common-Cause Failure and Recovery Factors The treatment of CCF in estimating the conditional CDF for CT and SF evaluations was discussed earlier. Also discussed are the appropriate considerations in modifying CCF terms modeled in the PRA (to include the effect of a component being unavailable because of failure, maintenance, or testing and for implementing a staggered test strategy). In addition, since the CCF contributions can be a dominant contributor, sensitivity analyses with respect to these parameters may be appropriate (see Regulatory Position 2.3.5 of this RG). Recovery factors used in the PRA model perhaps should be reviewed to learn whether the component assumed to be down because of failure is credited to be recovered. For example, consider that a TS change for an emergency diesel generator (EDG) is being evaluated, and conditional CDF for the EDG being down is being calculated. Then, if the cutsets used to calculate the conditional CDF take credit for the same EDG being recovered, such recovery factors should be modified. In such cases, no credit should be taken. A-1.3.4 Calculations of Transition Risk Transition risk is calculated to compare the risk of continuing operation in a given LCO to that of a transition to plant 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