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:
acceptable provided their technical basis is demonstrated with appropriate data and analyses. 3.12.2 Calculation of Post-Blowdown Thermal Hydraulics for Pressurized Water Reactors The refilling of the reactor vessel and the ulti mate reflooding of the core should be calculated by a best-estimate model that takes into consideration the thermal and hydraulic characteristics of the core, the emergency core cooling systems, and the primary and secondary reactor systems. The model should be ca pable of calculating the two-phase level in the reactor during the postulated transient. Best-estimate models will be considered acceptable provided their technical basis is demonstrated with appropriate data and analyses. 3.12.2.1 Model Evaluation Procedures for Post-Blowdown Thermal Hydraulics. A correlation or model to be used in ECCS evaluation to calculate level swell should be checked against an acceptable set of relevant data and should recognize the effects of depressurization, boil-off, power level, fluid conditions, and system geometry. The correlation proposed by Chexal, Horowitz, and Lellouche (Ref. 47) provides acceptable results when compared to experimental data reported in References 43, 48, 49, and 50. Uncertainties and bias of a correlation or model used to calculate level swell should be stated, as should the range of applicability. The primary coolant pumps should be assumed to be operating in the expected manner, based on the assumptions of Regulatory Position 3. 1, when calcu lating the resistance offered by the pumps to fluid flow. Models will be considered acceptable provided their technical basis is demonstrated through com parison with appropriate data and analyses. The total fluid flow leaving the core exit (car ryover) should be calculated using a best-estimate model that includes the effect of cross-flow on car ryover and core fluid distribution. Thermal-hydraulic phenomena associated with unique emergency core cooling systems, such as upper plenum