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:
ecified in paragraph 50.46(b). 4.2 Code Uncertainty This regulatory guide makes a distinction be tween the terms "code uncertainty" and "overall cal culational uncertainty." The latter term is defined "•-' above and includes the contributions to the uncer tainty described in Regulatory Positions 4.2 and 4.3. The components of the code uncertainty (i.e., the contribution to the overall uncertainty from the mod els and numerical methods used) are described in this section. Code uncertainty should be evaluated through di rect data comparison with relevant integral systems and separate-effects experiments at different scales. In this manner, an estimate of the uncertainty attrib utable to the combined effect of the models and cor relations within the code can be obtained for all scales and for different phenomena. Comparison to a sufficient number of integral systems experiments, from different test facilities and different scales, should be made to ensure that a reasonable estimate of code uncertainty and bias has been obtained. When necessary, separate-effects experiments should be used to establish code uncertainty for specific phe nomena (e.g., comparisons to Cylindrical Core Test Facility data to ascertain code uncertainty in model ing upper plenum injection performance). Code com parisons should account for limitations of the meas urements and calibration errors. These comparisons should be performed for im portant key parameters to demonstrate the overall best-estimate capability of the code. For large-break loss-of-coolant accidents, the most important key pa rameter is peak cladding temperature, which is ad dressed by one of the criteria of paragraph 50.46(b) and has a direct influence on the other criteria. In addition, a code uncertainty evaluation should be performed for other important parameters for the transient of interest to evaluate compensating errors. For small-break loss-of-coolant accidents, the clad ding temperature response is the most