Document: NUREG-0800
Document ID: 817bb0ad-6fd7-433e-aa2b-b4b3e1166f9c
Document Type: srp
Title: PROBABILISTIC RISK ASSESSMENT AND SEVERE ACCIDENT EVALUATION FOR
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0717/ML071700652.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
the applicant’s sensitivity studies performed to gain insights about the impact of uncertainties (and the potential lack of detailed models) on the estimated risk. The objectives of the sensitivity studies should include (1) determining the sensitivity of the estimated risk to potential biases in numerical values, such as initiating event frequencies, failure probabilities, and equipment unavailabilities, (2) determining the impact of the potential lack of modeling details on the estimated risk, and (3) determining the sensitivity of the estimated risk to previously raised issues (e.g., motor-operated valve reliability). For designs using passive safety systems and active defense-in-depth systems, the staff should review the sensitivity studies performed to investigate the impact of uncertainties on the PRA results under the assumption of plant operation without credit for the nonsafety-related defense-in-depth systems. These studies provide additional insights about the risk importance of the defense-in-depth systems that are taken into account in selecting nonsafety-related systems for regulatory treatment according to the RTNSS process. To have confidence that the applicant’s PRA and severe accident evaluation results and insights are adequate, the PRA staff must also determine that the scope, level of detail, and technical adequacy of the design-specific and plant-specific PRA are appropriate for the DC and COL, respectively, and any identified uses and risk-informed applications, as follows: 1. The applicant’s analyses should be comprehensive in scope, and address all applicable internal and external events and all plant operating modes. Since some aspects of the applicant’s approach may involve non-PRA techniques to address specific events (e.g., PRA-based seismic margins), the PRA staff review should ensure that the scope of the applicant’s analyses is appropriate for their identified uses and applications, which may involve a scope, level of