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:
§ 50.46 of 10 CFR Part 50, the licensee must demonstrate that the code and models used are acceptable and applicable to the specific fa cility over the intended operating range and must quantify the uncertainty in the specific application. General attributes expected in a best-estimate calcu lation are described here in Regulatory Position 1; special considerations for thermal-hydraulic best estimate codes are presented in Regulatory Position 2; and specific examples of features that are consid ered acceptable best-estimate models are given in Regulatory Position 3. Other models or correlations will be considered acceptable if their technical basis is demonstrated with appropriate data and analysis. A best-estimate model should provide a realistic calculation of the important parameters associated with a particular phenomenon to the degree practical with the currently available data and knowledge of the phenomenon. The model should be compared with applicable experimental data and should predict the mean of the data, rather than providing a bound to the data. The effects of all important variables should be considered. If it is not possible or practical to consider a particular phenomenon, the effect of ignoring this phenomenon should not normally be treated by including a bias in the analysis directly, but should be included as part of the model uncertainty. The importance of neglecting a particular phenome non should be considered within the overall calcula tional uncertainty. Careful consideration should be given to the range of applicability of a model when used in a best estimate code. When comparing the model to data, judgments on the applicability of the data to the situ ation that would actually occur in a reactor should be made. Correlations generally should not be extrapo lated beyond the range over which they were devel oped or assessed. If the model is to be extrapolated beyond the conditions for which valid data compari sons have been made, judgments