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:
analyses. Spe cific guidance regarding uncovered bundle heat trans fer is given in Regulatory Position 3.9.3. 3.16 Other Features of Best-Estimate Codes No list of best-estimate code features could be all-inclusive, because the important features of a best-estimate code may vary depending on the tran sient to be calculated and the required accuracy of the calculation. Because of this, no attempt has been made to construct an exhaustive list of best-estimate code features. Rather, features that were identified as 1.157-11 important for inclusion in Appendix K were used as a basis for the above list. These features are not neces sarily any more or less important than other code fea tures, but were highlighted because it is necessary to give specific examples of how current best-estimate models may vary from methods used traditionally in evaluation model codes using the various Appendix K conservatisms. In addition, models have not been included for areas in which the best model would be highly dependent on the specific plant design or the specific transient under consideration. The NRC staff believes that good examples of best-estimate thermal-hydraulic transient codes are those developed by the NRC (e.g., TRAC-PWR, TRAC-BWR, RELAPS, COBRA, and FRAP). Al though these codes are subject to further improve ment, based on their ongoing use and assessment, they currently provide reasonable best-estimate cal culations of the loss-of-coolant accident in a full-scale light-water reactor. This is substantiated through the code development and assessment literature gener ated by the NRC and its contractors over the past several years. It is possible, however, to describe in general how other features of best-estimate codes should be constructed. Two basic criteria should be 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