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:
rically arrived at break discharge coefficients to obtain a reasonable break flow. The uncertainties in the individual models that have not been evaluated by comparison to integral systems data should be quantified and used in the determination of overall code uncertainty. 4.4 Statistical Treatment of Overall Calculational Uncertainty The methodology used to obtain an estimate of the overall calculational uncertainty at the 95% prob ability limit should be provided and justified. If linear independence is assumed, suitable justification should be provided. The influence of the individual parameters on code uncertainty should be examined by making comparisons to relevant experimental data. Justification should be provided for the as sumed distribution of the parameter and the range considered. In reality, the true statistical distribution for the key parameters (e.g., peak cladding temperature) is unknown. The choice of a statistical distribution should be verified using applicable engineering data and information. The statistical parameters appropri ate for that distribution should be estimated using available data and results of engineering analyses. Supporting documentation should be provided for this selection process. These estimated values are as sumed to be the true values of the statistical param eters of the distribution. With these assumptions, an upper one-sided probability limit can be calculated at the 95% level. As the probability limit approaches 2200'F, more care must be taken in the selection and justification of the statistical distribution and in the estimation of its statistical parameters. If a normal distribution is selected and justified, the probability limit can be conservatively calculated using two standard deviations. The added conservatism of the two standard deviations compared to the 95th percentile is used to account for uncertainty in the probability distribution. Other techniques that account for the uncertainty in a more detailed