Document: NRC Regulatory Guide
Document ID: 5f799693-27fd-4e13-a5e1-4c02f393d90a
Document Type: regulatory_guide
Title: Best-Estimate Calculations of Emergency Core Cooling System Performance + HISTORY –HISTORY 04/2013 – Periodic Review of Revision 0 – Reviewed with issues identified for future consideration 03/1987 – Draft RS 701-4, Proposed Revision 0
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003739584.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.157
CFR Part: 
CFR Title: 

Content:
e applied, completeness and comparisons to experimental data. 3.16.1 Completeness Best-estimate codes should contain models in sufficient detail to predict phenomena that are impor tant to demonstrate compliance with the acceptance criteria specified in paragraph 50.46(b) of 10 CFR Part 50 (e.g., peak cladding temperature). Simplifi cations are acceptable as lopg as code uncertainties or biases do not become so large that they cast doubt on the actual behavior that would occur or on the true effect of assumed initial and boundary condi tions (e.g., equipment sizing, safety system settings). Comparisons of the overall calculations to integral ex periments should be performed to ensure that impor tant phenomena can be predicted and to help in making judgments on the effect of code simplifica tions. Consideration should also be given to the un certainty and validity of the experiment to ensure that meaningful comparisons are being made. 3.16.2 Data Comparisons Individual best-estimate models should be com pared to applicable experimental data to ensure that realistic behavior is predicted and that relevant ex perimental variables are included. Uncertainty analy ses are required to ensure that a major bias does not exist in the models and that the model uncertainty is small enough to provide a realistic estimate of the ef fect of important experimental variables. Uncertainty analyses should also consider experimental uncer- tainty to ensure that meaningful comparisons are be ing made. 4. ESTIMATION OF OVERALL CALCULATIONAL UNCERTAINTY 4.1 General The term "uncertainty," when applied to best estimate thermal-hydraulic transient codes, is used at two levels. At the lower or more detailed level, the term refers to the degree to which an individual model, correlation, or method used within the code represents the physical phenomenon it addresses. These individual uncertainties, when taken together, comprise the "code uncertainty." The combined uncertainty associated with