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:
. Critical flow models to be employed in ECCS evaluations should: a. Be checked against an acceptable set of rele vant data, b. Recognize thermal nonequilibrium conditions when the fluid is subcooled, and c. Provide a means of transition from nonequi librium to equilibrium conditions. The uncertainties and bias of a correlation or model used to calculate critical flow should be stated, as well as their range of applicability. The mechanistic thermal nonequilibrium and slip model of Richter (Ref. 12) compares well to small and large-scale test data (Ref. 13). 3.4.1.2 Experimental Data for Discharge Flow Rate. An acceptable set of relevant critical flow data should cover the fluid conditions, geometries, and types of breaks pertinent to light-water reactor loss-of-coolant accidents. The following tests should be considered in establishing an acceptable set of relevant data: "* Marviken tests (Ref. 14) "* Moby Dick experiments (Ref. 15) "* Brookhaven critical flashing flows in nozzles (Ref. 16) "* Sozzi-Sutherland tests (Ref. 17) "* Edwards experiments (Ref. 18) "* Super Moby Dick experiments (Refs. 19 and 20) For critical flow from small breaks under strati fied conditions, currently acceptable test data for as sessing models and codes include those reported by: "* Anderson and Owca (Ref. 21) "* Reimann and Khan (Ref. 22) "* Schrock et al. (Refs. 23 and 24) 3.4.2 ECC Bypass The best-estimate code should contain a calcula tion of the amount of injected cooling water that by passes the vessel during the blowdown phase of the loss-of-coolant accident. The calculation of ECC by pass should be a best-estimate calculation using analyses and comparisons with applicable experimen tal data. Although it is clear that the dominant proc esses governing ECC bypass are multidimensional, single-dimensional approximations justified through sufficient analysis and data may be acceptable. Best estimate methods will be considered acceptable pro vided their technical basis is