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:
the assumption being made. An assumption is considered “key” when it may influence (i.e., have the potential to change) the decision being made. NUREG-1855 provides useful insights related to this expectation. • The event trees and fault trees that require modification to support analyses of the proposed change with a description of their modification. • A list of operator actions modeled in the PRA that impact the application and their error probabilities. The submitted information that summarizes the results of the risk assessment should include the following: • The effects of the proposed change on the more significant sequences (e.g., sequences that contribute more than five percent to the risk) to show that the licensing basis change does not create risk outliers and does not exacerbate existing risk outliers. • An assessment of the change to CDF and LERF, including a description of the significant contributors to the change and an assessment of the realism with which those contributors have been evaluated. • Information related to the assessment of the full-scope, base CDF; the extent of the information needed depends on whether the analysis of the change in CDF is in Region II or Region III of Figure 4. • Information related to the assessment of the full-scope, base LERF; the extent of the information needed depends on whether the analysis of the change in LERF is in Region II or Region III of Figure 5. • Results of sensitivity analyses that show that the conclusions regarding the impact of the licensing basis change on plant risk do not vary significantly under a different set of plausible assumptions. 6.3.2 Cumulative Risks As part of evaluation of risk, licensees should understand the effects of the current application in light of past applications. Optimally, the PRA used for the current application should already model the effects of past applications. However, qualitative effects and synergistic effects are sometimes difficult to