VALIDATION OF SYSTEM ANALYSIS MODULE AXIAL MIXING MODEL FOR THERMAL STRATIFICATION AND MIXING APPLICATION IN THE UPPER PLENUM OF A LIQUID METAL REACTOR

Liquid metals are being investigated as reactor coolants due to their high thermal conductivity and effectiveness at high temperatures. System analysis codes are being developed to model advanced, non-light water reactors, such as liquid metal-cooled reactors. One such code being developed is System Analysis Module (SAM) at Argonne National Laboratory, which contains capabilities for core neutronics, heat transfer, and fluid flow. System fluid dynamics are solved using a hybrid finite element/volume method with the geometry modelled as 0D or 1D components. Low-Prandtl number coolants, such as liquid metals, can result in thermal stratification, which can affect heat removal in the upper plenum of the reactor. Stratification and thermal mixing are modelled within SAM using a modified energy conservation equation which includes terms to account for mixing from local flow velocity, geometry, and buoyancy effects. While this mixing model has been validated against high-fidelity CFD models, more rigorous validation is needed. An established, scaled liquid metal test facility that uses gallium as a surrogate fluid has been constructed to investigate the stratification and thermal mixing of low-Prandtl number fluids in the upper plenum of a liquid metal-cooled reactor. This facility is used to validate the 1D axial mixing model and 0D mixing models in SAM using multiple geometries and mixing parameters. The resultant temperatures are then compared with the experimental temperatures to validate the mixing model and to better correspond mixing parameters with various flow scenarios.