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:
ptable methods such as those described i n the subject regulatory guide t h a t predict a through-wall crack penetration frequency less than 5 x per reactor year. The mean frequency o f reactor vessel through-wall crack penetration i s used as the principal acceptance c r i t e r i o n because the s t a f f ' s analyses p r e d i c t t h a t there i s a high l i k e l i h o o d o f core damage i n the event o f such cracks. Core damage events have potential public health and safety consequences t h a t are d i f f i c u l t t o analyze w i t h certainty. They would also have severe economic impacts upon the licensee and the public who w i l l pay for cleanup and replace- ment power. For a l l these reasons, reactor vessel through-wall crack penetra- t i o n frequency i s used as the p r i n c i p a l acceptance c r i t e r i o n . The p a r t i c u l a r value o f 5 x mean frequency per reactor year was selected as an achievable, r e a l i s t i c goal t h a t w i l l r e s u l t i n an acceptable level o f r i s k . It i s believed t h a t t h i s value i s acceptably low considering t h a t pressure vessel f a i l u r e i s not p a r t o f the design basis o f the p l a n t and therefore must have a frequency low enough t o be considered incredible. When the various (unquantifiable) biases t h a t are inherent i n the analyses are taken i n t o account a t l e a s t q u a l i t a t i v e l y , such as the i m p l i c i t assumption t h a t "core damage" i s equivalent to "core melt," this value probably results in a core me1 t mean frequency close I I to one per mil 1 ion reactor years. k In the opinion of the NRC staff, there are no practical quantities on which t o base the acceptance criteria other than reactor vessel through-wall cracks (i. e., vessel failure). UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE, $300 USNRC PERMIT No. G-67 1 I I