Document: NRC Regulatory Guide
Document ID: da2e0703-3488-44b0-b6d0-089aac7cae3d
Document Type: regulatory_guide
Title: Format and Content of Plant-Specific Pressurized Thermal Shock Safety Analysis Reports for Pressurized Water Reactors
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740028.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.154
CFR Part: 
CFR Title: 

Content:
ncerning PTS risk analyses. This experience has come from performance of analyses by the staff, from prototype plant-specific analyses performed by national laboratories and sponsored by NRC, and from review of industry-sponsored analyses. The regula- tory guide reflects the lessons learned from this experience and will aid 1 icensees in performing analyses that wi 11 efficiently derive risk estimates in the form the NRC needs for use in evaluating their conformance with the regulations. This need for guidance i s particularly acute since the plant-specific PTS analyses should use a probabi 1 i s t i c risk analysis (PRA) approach, as opposed to the more traditional design basis accident (DBA) approach, as explained be1 ow. The PTS risk i s developed as the sum of the small risks resulting from each of a large number of possible (but unlikely) PTS events. The regulatory guide accordingly describes acceptable methods to identify as many as possible of the potential PTS events, group them, calculate the frequencies and conse- quences of each group, determine the risk due to each group by multiplying the predicted frequency by the calculated consequences, and then sum the results "Reference Temperature for the Nil Ductility Transition, a measure of the temperature range i n which the materials' ductility changes most rapidly with changes i n temperature. from a1 1 groups t o obtain t o t a l PTS r i s k estimates t h a t can be compared w i t h the acceptance c r i t e r i a given i n the regulatory guide. The DBA approach, on the other hand, would attempt t o define a worst cred- i b l e event (the "design basis accident") and then show t h a t (1) consequences from t h a t event are acceptable and (2) a l l other credible events are less severe and therefore acceptable. The s t a f f has determined t h a t t h i s DBA approach i s not appropriate f o r plant-specific PTS analyses because the t o t a l r i s k from a l l credible PTS events can be s i g n i f i c a n