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:
was done i n the ORNL studies (Refs. 1, 2, and 3) by using what have been called system state trees. These trees define the potential states o f each plant system o f interest conditional on specific thermal-hydraulic conditions. I n i t i a t o r - s p e c i f i c event trees can then be developed by examining the system state trees with respect t o each i n i t i a t i n g event. A similar or equivalent approach should be used to ensure traceability of the event trees and to ensure that important sequences are not inadvertently el imi nated. Support system failures should also be presented within some type of event tree structure. If the event trees are developed as previously described, any support system failure would most likely lead to a sequence of events that i s already mapped out on the event trees, b u t in many instances with a higher pro- bability of occurrence. In other cases, i t may be necessary t o define event trees resulting from a support system failure. In either case, i t i s important that the support systems be examined to identify their potential impact on over- cooling conditions. The results of this examination should be presented as a separate section with the identification of specific support system failure sequences of interest. The support system review should a t least include: " The electrical supply system. O The compressed a i r instrument system. O The component and service water systems. Operator Effects The operator effects are analyzed in two separate sections. In this sec- tion the potential operator actions are identified. These actions are further analyzed in Section 3.4 in which the probabilities associated w i t h the perfor- mance o f an operator action are developed. I The operator can improve, aggravate, or initiate an overcooling transient. 1 All three of these categories should be discussed in this section. . 1. Procedures and/or the operators1 general knowledge can lead t o actions that improve the conditions