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:
r e o f two identical components. One could then assume that, a f t e r the f a i l u r e o f three components o f the same type, a l l remaining components o f t h a t type i n the same o r i n other systems being subjected t o the same environment o r f a u l t causes would f a i l w i t h a p r o b a b i l i t y o f 1.0. The licensee should discuss how these types o f coupled f a i l u r e s are handled i n the analysis. Common cause f a i l u r e s o f a d i f f e r e n t type may occur, as previously dis- cussed, through the f a i l u r e o f a support system or a control signal. An anal- y s i s o f these potential f a i l u r e s should be made and the branch p r o b a b i l i t i e s should be adjusted whenever appropriate. 3.4.3 Operator Actions Operator action p r o b a b i l i t i e s are p a r t i c u l a r l y d i f f i c u l t t o determine because o f the lack o f a data base. The problem i s f u r t h e r complicated when time becomes an important variable. The procedure outlined below represents one approach t o quantifying operator actions. This procedure shoul d be conser- vative f o r any operator action ~erformed as required by procedures assuming i, t h a t the equipment required i s operational. For operator actions t h a t might not be associated w i t h procedural steps, it i s not clear t h a t t h i s s i m p l i f i e d approach would produce conservative frequencies. Therefore, the approach described would only be recommended f o r operator actions associated w i t h proce- dural steps. Regardless o f the method used, the human e r r o r p r o b a b i l i t i e s used i n these analyses should be supported by data validated f o r the p l a n t being analyzed. 1. I d e n t i f y operator actions - I n t h i s step the procedures associated w i t h each i n i t i a t o r would be reviewed t o i d e n t i f y those operator actions t h a t 7 would have an impact on downcomer temperature. 2. I d e n t i f y time constraint - I n the case o f