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:
The break location and ECCS injection point are areas of high fluid velocity and complex fluid flow and contain phenomena that are often difficult to cal culate. The results of these calculations are often highly dependent on the noding. Sufficient sensitivity studies should be performed on the noding and other important parameters to ensure that the calculations provide realistic results. 3.6 Frictional Pressure Drop The frictional losses in pipes and other compo nents should be calculated using models that include variation of friction factor with Reynolds number and account for two-phase flow effects on friction. Best estimate models will be considered acceptable pro vided their technical basis is demonstrated with ap propriate data and analyses. 3.6.1 Model Evaluation Procedure for Frictional Pressure Drop A model for frictional pressure drop to be used in ECCS evaluation should: a. Be checked against a set of relevant data, and b. Be consistent with models used for calculat ing gravitational and acceleration pressure drops. If void fraction models or correlations used to calculate the three components of the total pressure drop differ one from another, a quantitative justification must be provided. Uncertainties and bias of a correlation or model should be stated as well as the range of applicability. 3.6.2 Experimental Data for Frictional Pressure Drop An acceptable set of relevant data should cover, as far as possible, the ranges of parameters (mass flux, quality, pressure, fluid physical properties, roughness, and geometries) that are found in actual plant applications. The following tests should be con sidered in establishing an acceptable set of relevant data: * Vertical tubes CISE test (Refs. 33 and 34) * Horizontal tubes GE tests (Refs. 35 and 36) * Rod 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