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:
od bundles GE tests (Ref. 37) 3.7 Momentum Equation The following effects should be taken into account in the two-phase conservation of momentum equation: (1) temporal change in momentum, (2) momentum convection, (3) area change momen tum flux, (4) momentum change due to compressibil ity, (5) pressure loss resulting from wall friction, (6) pressure loss resulting from area change, and (7) gravitational acceleration. Best-estimate models will be considered acceptable provided their technical basis is demonstrated with appropriate data and analyses. 3.8 Critical Heat Flux Best-estimate models developed from appropri ate steady-state or transient experimental data should be used in calculating critical heat flux (CHF) during loss-of-coolant accidents. The codes in which these models are used should contain suitable checks to en sure that the range of conditions over which these correlations are used are within those intended. Re search has shown that CHF is highly dependent on the fuel rod geometry, local heat flux, and fluid con ditions. After CHF is predicted at an axial fuel rod location, the calculation may use nucleate boiling heat transfer correlations if the calculated local fluid and surface conditions justify the reestablishment of nucleate boiling. Best-estimate models will be consid ered acceptable provided their technical basis is dem onstrated with appropriate data and analyses. 3.9 Post-CHF Blowdown Heat Transfer Models of heat transfer from the fuel to the sur rounding fluid in the post-CHF regimes of transition and film boiling should be best-estimate models based on comparison to applicable steady-state or transient data. Any model should be evaluated to demonstrate that it provides acceptable results over the applicable ranges. Best-estimate models will be considered ac ceptable provided their technical basis is demon strated with appropriate data and analyses. 3.9.1 Model Evaluation Procedure for Post-CHF Heat Transfer A model to be used in ECCS