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:
le pump speed as a function of time. The pump model resistance and other empirical terms should be justified through comparisons with applicable data. The pump model for the two-phase region should be verified by comparison to applicable two-phase per formance data. Pump coastdown following loss of power should be treated in a best-estimate manner. A locked rotor following a large-break loss-of-coolant accident need not be assumed unless it is calculated to occur. Best-estimate models will be considered ac ceptable provided their technical basis is demon strated with appropriate data and analyses. 3.11 Core Flow Distribution During Blowdown The core flow through the hottest region of the core during the blowdown should be calculated as a function of time. For the purpose of these calcula tions, the hottest region of the core should not be greater than the size of one fuel assembly. Calcula tions of the flow in the hot region should take into account any cross-flow between regions and any flow blockage calculated to occur during the blowdown as a result of cladding swelling or rupture. The numeri cal scheme should ensure that unrealistic oscillations of the calculated flow do not result. Best-estimate models will be considered acceptable provided their technical basis is demonstrated with appropriate data and analyses. 1.157-9 3.12 Post-Blowdown Phenomena 3.12.1 Containment Pressure The containment pressure used for evaluating cooling effectiveness during the post-blowdown phase of a loss-of-coolant accident should be calculated in a best-estimate manner and should include the effects of containment heat sinks. The calculation should in clude the effects of operation of all pressure-reducing equipment assumed to be available. Best-estimate models will be considered 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