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:
his must include comparison with the acceptance c r i t e r i a described be1 ow o f the PTS-related through-wall crack frequency with corrective actions implemented as necessary. S t a f f Review o f Plant-Speci f i c PTS Safety Analysis Reports and Acceptance C r i t e r i a f o r Continued Operation The PTS r u l e specifies a screening c r i t e r i o n based on RTNDT (called RTpTS f o r use as defined within the rule) o f 270°F f o r axial weld and plate materials and 300°F f o r circumferential weld materials. As detailed i n SECY-82-465 (Ref. 4), these values were selected based on generic studies o f the expected frequency and character o f a wide spectrum o f transients and accidents t h a t could cause pressurized overcool i n g o f the reactor vessel (PTS events) and on operating experience data. The r i s k due t o PTS events was assessed i n terms o f probabilistic fracture mechanics calculations o f the expected frequency o f through-wall crack penetration o f the pressure vessel due t o the PTS events. I n selecting the screening c r i t e r i o n based on those calculations, the conserva- t i v e assumption was made t h a t any through-wall crack could r e s u l t i n severe core degradation o r melt. Core melt i t s e l f was viewed as an event t o be avoided even though r i s k t o the public due t o such an event i n terms o f person- rems and early and l a t e f a t a l i t i e s was not calculated with any certainty. The estimated through-wall crack frequency developed as a function o f RTNOT f o r axial welds (Fig. 8.3 o f Ref. 4) i s shown i n Figure 1. LONGITUDINAL CRACK EXTENSION NO ARREST 1 o - ~ SECY-82-465 PRA RESULTS I 1 1 1 I 1 k LEGEND: MEAN SURFACE RTNDT(*F) Figure 1 The RTpTS screening criterion selected by the staff corresponds to a mean I (or average) "best estimate'' surface RTpTS of 210°F. The staff used a "2-sigma" -L value (spread between "best estimate" and "upper limit") of 60°F;* thus the screening criterion expressed in