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
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CFR Title: 

Content:
conservative bias or simplifi cation in otherwise best-estimate codes should not, 1.157-3 however, result in calculations that are unrealistic, that do not include important phenomena, or that contain bias and uncertainty that cannot be bounded. Therefore, any calculational procedure determined to be a best-estimate code in the context of this guide or for use under paragraph 50.46(a)(i) should be compared with applicable experimental data to en sure that the calculation of important phenomena is realistic. 2. CONSIDERATIONS FOR THERMAL HYDRAULIC BEST-ESTIMATE CODES Some features that are acceptable for use in best-estimate codes are described in the following paragraphs. Models that address these features may be used with the basic proviso that a specific model is acceptable if it has been compared with applicable experimental data and shown to provide reasonable predictions. Reference 7, "Compendium of ECCS Research for Realistic LOCA Analysis" (NUREG-1230), provides a summary of the large ex perimental data base available, upon which best estimate models may be based. While inclusion in Reference 7 does not guarantee that the data or model will be acceptable, the report describes and references a large body of data generally applicable to best-estimate models. NUREG-1230 also provides documentation of NRC studies of the effect of reac tor power increase on risk, background information on the ECCS rule, and a description of the methodol ogy developed by NRC for estimating thermal hydraulic transient code uncertainty. For any models or correlations used in a best estimate code, sufficient justification must be pro vided to substantiate that the code performs ade quately for the classes of transients to which it applied. In general, the features of best-estimate thermal-hydraulic transient codes have uncertaintie associated with their use for predicting reactor syster response. These uncertainties should be considered as part of the overall uncertainty analysis