Credibility Assessment Framework for Critical Boiling Transition Models: A generic safety case to determine the credibility of critical heat flux and critical power models, Draft for Comment (NUREG/KM-0013)

This publication has been issued for public comment. Comments will be accepted until May 24, 2019. To submit comments, please see Docket ID Number NRC–2019-0043.

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Publication Information

Date Published: March 2019

Prepared by:
J.S. Kaizer
R. Anzalone
E. Brown
M. Panicker
S. Haider
J. Gilmer
T. Drzewiecki
A. Attard (retired, unable to comment on final version)

Office of Nuclear Reactor Regulation
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Abstract

Critical boiling transition (CBT) occurs when a flow regime that has a higher heat transfer rate transitions to a flow regime that has a significantly lower heat transfer rate. Models that predict a CBT are a necessary part of reactor safety analysis because they are used to determine plant safety limits. Therefore, the review of CBT models has been a focus of the U.S. Nuclear Regulatory Commission (NRC) since its inception in 1975.

This work presents a generic safety case in the form of a credibility assessment framework that combines aspects of goal structuring notation and maturity assessment. This framework is focused on the credibility assessment of CBT models with specific application to reactor safety analysis. The NRC has performed many such assessments and has generated this framework based on the experience of current and former NRC staff, as well as previous staff reviews as summarized in staff evaluations. This document includes a survey of the important technical and regulatory literature; a detailed technical discussion of CBT models and their application; and a suggested framework for CBT models. This NUREG/KM summarizes the knowledge the NRC staff has developed over the course of 40 years of CBT model and analysis reviews.