Document: NUREG-0800
Document ID: ac43f632-9db1-4857-9f56-bfba45965456
Document Type: srp
Title: * These are modifications to a plant’s design, operations, or other activities that require NRC approval. These modifica
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0232/ML023250195.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19
CFR Part: 
CFR Title: 

Content:
ccurring 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 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 SRP 19-A22 presents a screening approach to evaluate the frequencies of dominant containment failure modes and bypass events. The purpose of this approach is to provide estimates of LERF, given certain characteristics of core damage sequences as input. The review approach presented in this SRP section builds upon the underlying insights from draft NUREG/CR-6595. For each major containment type, particular considerations are suggested for attention in the review process. However, it is not intended to suggest that these considerations exhaust the technical issues that affect the potential for large early release. For example, where plant-specific PRA Level 2 analyses exist, these could provide further insights into LERF considerations for that plant. For each major containment type, the factors that most strongly affect the potential for large early release (given that a core damage sequence is underway) are as follows: PWR Large Dry: Containment bypass Containment isolation RCS depressurization Emergency core cooling (ECC) restoration before vessel failure PWR Ice Condenser: Containment isolation Containment bypass Hydrogen igniters RCS depressurization ECC restoration before vessel failure BWR Mark I and II: Containment isolation