Document: NRC Regulatory Guide
Document ID: 22ccfd5e-c5d8-4615-a02c-32369aa9f533
Document Type: regulatory_guide
Title: Acceptability of Probabilistic Risk Assessment Results for Risk-Informed Activities (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1930/ML19308B636.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.200
CFR Part: 
CFR Title: 

Content:
d groups and modes of operation) included in the PRA to support the decision 3.1 Scope of Risk Contributors Addressed by the PRA Model Based on the definition of the application, and in particular the acceptance criteria or guidelines, the scope of risk contributors (internal and external hazards and plant operating modes) for the PRA should be identified. For example, if the application is designed around using the acceptance guidelines of RG 1.174, the evaluations of CDF, the change in CDF (i.e., ΔCDF), LERF, and the change in LERF (i.e., ΔLERF) should be performed with a full-scope PRA, including all hazard groups and all modes of operation. However, since many PRAs are not full-scope and do not include models for all risk contributors, decision-makers should allow for such omissions. Examples of allowances that may be made for omitted PRA scope items include using compensatory measures, restricting the implementation of the proposed change to those aspects of the plant covered by the risk model, and using bounding analyses to show the risk contribution is likely not greater than a certain value. However, it should be noted that, consistent with the Commission-endorsed phased PRA quality initiative, all risk contributors that cannot be shown to be insignificant to the decision should be assessed through quantitative risk assessment methods to support risk-informed licensing actions. This RG is focused specifically on the acceptability of the PRA information used in support of a decision and does not address the acceptability of non-PRA information used to justify the omission of PRA scope items. The national consensus PRA standards and industry PRA programs that have been developed, or are in the process of being developed, address a specific scope. For example, the ASME/ANS Level 1/LERF PRA standard and NEI 17-07, Revision 2, addresses a Level 1 and limited Level 2 PRA analysis for all hazards (i.e., internal events, internal flood, internal fire, seismic,