Document: NUREG-0800
Document ID: dd4f84a9-8976-44c4-b631-d7c0254f4efc
Document Type: srp
Title: PROBABILISTIC RISK ASSESSMENT AND SEVERE ACCIDENT EVALUATION FOR
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1416/ML14161A594.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
ity and the assumptions in the risk analyses are justified. In some cases the reviewer may need to engage reviewers from other technical branches that have expertise in particular areas (e.g., systems operation, T-H performance, operating experience). Reviewers should therefore be aware of the following issues related to safety during non-power modes of operation: A. Based on previous PRAs, studies by the EPRI and studies performed by the staff, roughly 80 percent of risk for traditional PWR designs occurs during periods when the reactor coolant system is drained and open (midloop operation is a subset of this condition). B. The time it takes to reach boiling in the reactor vessel following loss of the decay heat removal function can be very short during PWR midloop operation (e.g. 12 minutes). Steaming into the containment will lead to intolerable conditions that could seriously affect the ability of personnel to close the containment. C. During reduced inventory operation in a PWR a large vent for the reactor coolant system (RCS), such as a hot leg SG plenum man way, is necessary before opening a cold leg penetration to prevent expelling water from the core following a loss of residual heat removal. RCS piping penetrations may exist below the active fuel and pathways may exist via connected systems that could lead to draining the reactor vessel. In these cases reviewers should identify the isolation functions available and operable and assure that they are treated accurately in the PRA model. 19.0-28 Draft Revision 3 –November 2014 Design-Specific PRA (PRA-Based SMA) 1. Staff responsible for the review of the description and results of the applicant’s PRA review the design-specific plant system and accident sequence analysis in accordance with the acceptance criteria given in Section II of this SRP. 2. Staff responsible for the review of the seismic and structural design of the facility review (1) the applicant’s evaluation of seismic fragilities, and (2)