An Efficient 1-D Thermal Stratification Model for Pool-Type Sodium-Cooled Fast Reactors

Abstract

Investigating thermal stratification in the upper plenum of a Sodium Fast Reactor (SFR) is currently a technology gap in SFR safety analysis. Understanding thermal stratification will promote safe operation of the SFR before its commercial deployment. Stratified layers of liquid sodium with a large vertical temperature gradient could be established in the upper plenum of an SFR during a down-power or a loss-of-flow transient. These stratified layers are unstable and could result in uncertainties for the core safety of an SFR. In order to predict the occurrence of the thermal stratification efficiently, we developed a 1-D transport model to estimate the temperature profile of the ambient fluid in the upper plenum. This model demands much less computational efforts than CFD codes and provides calculations with higher fidelity than historical system-level codes. Two flow conditions were considered separately in the current study depending on if in-vessel components are presented in the upper plenum. For the condition where in-vessel components, specifically the upper internal structure, are presented, we assumed that the impinging sodium was evenly dispersed in the ambient fluid within the distance between the bottom of the in-vessel

Development and Validation of SAM Multi-dimensional Flow Model for Thermal Mixing and Stratification Modeling

“…For a transient where an initially stratified pool is gradually mixed, it cannot help to infer the time scale for such mixing processes. Two recent efforts have been made to develop 1-D models for thermal stratification with the support of the two NEUP projects, one by Wilson and Bindra [17] and the other by Lu et al [18]. However, the two approaches have similar limitations to the work from UC Berkeley, as mentioned above.…”