Document: NRC Regulatory Guide
Document ID: 82659041-98b0-4721-b25d-c4fb2ea394d0
Document Type: regulatory_guide
Title: An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1635/ML16358A153.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.174
CFR Part: 
CFR Title: 

Content:
y Goal Policy Statement. For purposes of implementation, the licensee should assess the expected change in CDF and LERF. For licensing basis changes that may have a substantial impact, an in-depth and comprehensive risk assessment, in the form of a PRA (i.e., a PRA that is appropriate to derive the total impact of the proposed licensing basis change) may be necessary to provide acceptable justification. As discussed in RG 1.200, a method or approach is considered to be a PRA when the method or approach (1) provides a quantitative assessment of the identified risk in terms of scenarios that result in undesired consequences (e.g., core damage or a large early release) and their frequencies, and (2) is comprised of specific technical elements in performing the quantification.” Section C.1.2 of RG 1.200 defines the technical elements. As discussed in Section C.2.4, the risk acceptance guidelines are intended for comparison with the results of a full scope risk assessment. However, the necessary sophistication of the evaluation, including the scope of the PRA (e.g., internal hazards only, at-power only), depends on the contribution the risk assessment makes to the integrated decisionmaking, which depends to some extent on the magnitude of the potential risk impact. It should be noted that because the hazards and plant operating states are independent, addition of the mean value risk results (also referred to as “aggregation” of the results) of the contributions is mathematically correct. In other applications, calculated risk-importance measures or bounding risk calculations may be adequate. In still others, a qualitative assessment of the impact of the licensing basis change on the plant’s risk may be sufficient. The remainder of this section discusses the use of quantitative PRA results in decisionmaking. This discussion has three parts: • A fundamental element of NRC’s risk-informed regulatory process is a PRA of sufficient scope, level of detail,