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:
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 injection and upper head injection, should be accounted for. The effects of the compressed gas in the accumulator fol lowing accumulator water discharge should be in cluded in the calculation. Any model or code used for this calculation should be assessed against applica ble experimental data. Reference 7 describes a large body of refill/reflood thermal-hydraulic data obtained from the 2D/3D program that is appropriate for consideration. 3.12.2.2 Experimental Data for Post Blowdown Thermal Hydraulics. The following tests should be considered when establishing an acceptable set of relevant data: "* GE tests (Refs. 48 and 51) "* ORNL tests (Refs. 43 and 49) "* FLECHT-SEASET test (Ref. 45) "* THETIS tests (Ref. 50) 3.12.3 Steam Interaction with Emergency Core Cooling Water in Pressurized Water Reactors The thermal-hydraulic interaction between the steam or two-phase fluid and the emergency core cooling water should be taken into account in calcu lating the core thermal hydraulics and the steam flow through the reactor coolant pipes during the time the accumulators are discharging water. Best-estimate models will be considered acceptable provided their technical basis is demonstrated with appropriate data and analyses. 3.12.4 Post-Blowdown Heat Transfer for Pressurized Water Reactors During refilling of the reactor vessel and ultimate reflooding of the core, the heat transfer calculations should be based on a best-estimate calculation of the fluid flow through the core, accounting for unique emergency core cooling systems. The calculations should also include the effects of any flow blockage calculated to occur as a result of cladding swelling or rupture. Heat transfer calculations that account for two-phase conditions in the core during refilling of the reactor vessel