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:
posed CT (i.e., the subject equipment is inoperable) and there are no additional failures. Such an assessment should result in identifying all situations in which entry into the condition addressed by the proposed CT could result in failure to meet an intended safety function. 2.3 Evaluation of Risk Impact (Principle 4) Consistent with Principle 4 in RG 1.174, the NRC staff has identified the following three-tiered approach for licensees to evaluate the risk associated with proposed TS CT changes: a. Tier 1 is an evaluation of the impact on plant risk of the proposed TS change as expressed by the change in core damage frequency (ΔCDF), the incremental conditional core damage probability (ICCDP),1 the change in large early release frequency (ΔLERF), and the incremental conditional large early release probability (ICLERP).2 To support this evaluation, two aspects are to be considered: (1) the acceptability of the PRA and (2) the PRA insights and results. The licensee should demonstrate that its PRA is acceptable for assessing the proposed TS change, identify the impact of the TS change on plant risk, and demonstrated that this impact on plant risk is acceptable. b. Tier 2 is an identification of potentially high-risk configurations that could exist if equipment, in addition to that associated with the change, is taken out of service simultaneously or if other risk-significant operational factors, such as concurrent system or equipment testing, are also 1 ICCDP = ((conditional CDF with the subject equipment out of service and nominal expected equipment unavailabilities for other equipment permitted to be out of service by the TS) − (baseline CDF with nominal expected equipment unavailabilities)) × (total duration of a single CT under consideration). 2 ICLERP = ((conditional LERF with the subject equipment out of service and nominal expected equipment unavailabilities for other equipment permitted to be out of service by the TS) − (baseline LERF with nominal