Document: NUREG-0800
Document ID: e32f0820-4e33-476e-aa36-4ca8c2c64af0
Document Type: srp
Title: Use of Probabilistic Risk Assessment in Plant-Specific, Risk-Informed Decisionmaking:
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0119/ML011940192.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
viewers identify the major items related to functional plant capability that directly affect the potential for large early release; to direct reviewers in establishing whether the proposed changes can affect this capability; and to determine whether the licensee has appropriately addressed these items in estimating changes in LERF. b. Review Guidance and Procedures There are several ways in which a change to the plant's design or operation can significantly alter LERF, including those that: Change the frequency of containment bypass sequences (e.g., steam generator tube ruptures and interfacing system LOCAs). Change the frequency of core damage sequences that pose severe challenges to containment (e.g., sequences resulting in elevated reactor coolant system (RCS) pressure during core damage and at vessel failure). Change the performance of systems involved in containment safety functions (e.g., containment isolation, containment heat removal, containment sprays, hydrogen control, etc.). Change the performance of systems or operator actions that affect accident management strategies (e.g., depressurization, venting, etc.). Change the frequency of core damage sequences occurring at shutdown with containment functionality reduced. The guidance provided below focuses, for each plant type, on particular examples of these general categories. Based on previous PRAs, draft NUREG/CR-6595 developed some insights on the factors that most strongly affect the estimated likelihood of a large early release. Although SRP 19-A21 plant-specific details may' become significant in some cases, it was found that plants of each major containment type tend to be similar in the types of sequences that could lead to a large early release, reflecting strengths and weaknesses of that containment structure and particular features of the core damage sequences that characterize that plant type. Based on these insights, draft NUREG/CR-6595 presents a screening approach to evaluate the frequencies