Comparative CFD analyses of liquid metal cooled reactor for lunar surface power

Abstract

This paper presents the results of comparative CFD and thermal-hydraulics analyses of the Solid Core–Sectored Compact Reactor (SC-SCoRe) for lunar surface power. This fast-neutron spectrum, liquid NaK-56 cooled reactor is loaded with highly enriched UN fuel. It nominally generates 1.0MWth for ∼21 full-power years at NaK-56 inlet and exit temperatures of 850K and 900K. The analyses examine the realizable two-layer k–ɛ and the Shear Stress Transport (SST) k–ω turbulence models, with different numerical mesh refinements, for simulating the performance of the SC-SCoRe core during nominal operation as well as investigate the effect on the computation time and calculated parameters. In addition, the results calculated for a single tri-lobe flow channel are compared to those obtained using the Detached Eddy Simulation (DES), a hybrid LES and RANS turbulence model. The numerical mesh refinement beyond 2×107 cells in the flow channels and the choice of turbulence model slightly affect the calculated fuel, core structure, and liquid metal temperatures. They more strongly affect the pressure losses and the intensity of flow mixing and the formation of turbulence eddies in the inlet and exit plenums and exit duct. With the same numerical mesh refinements, the total computation time with the k–ω model is 40–120% longer than with the k-ɛ model, while the calculated operation parameters are almost identical. The flow field provided by the k–ω model offers finer details of the flow mixing and the eddy vortices forming in the upper plenum and the exit duct. Comparisons of the heat transfer and pressure loss results of the DES model to those of the k–ɛ and k–ω turbulence models for a single tri-lobe, show the calculated temperatures, velocity profiles, and pressure losses differ only slightly. The DES model results of the Nusselt number along the channel are consistently higher than those calculated using the k–ω and the k–ɛ models. The time to complete the calculations with the DES model, on the same hardware, was 38 and 86 times that with the k–ω and the k–ɛ models, respectively. The results for NaK-56 liquid flow in a circular tube with uniformly heated wall show that the Nu values using the k–ω and k–ɛ turbulence models are consistent with the reported empirical correlations.