Numerical Simulation of Thermal–Hydraulic Processes in Liquid-Metal Cooled Fuel Assemblies in the Anisotropic Porous Body Approximation

The article presents an anisotropic porous body model in which the transfer anisotropy is taken into account through determining—by means of tensor analysis techniques—the drag force, effective viscosity, and thermal conductivity. The model is intended for describing heat-and-mass transfer in fuel assemblies and tube bundles. For closing the system of anisotropic porous body equations, the integral turbulence model developed by the authors is used. To verify how correctly the hydrodynamics and heat transfer are described, a few hydrodynamic and thermal–hydraulic processes in water- and liquid-metal-cooled fuel rod assemblies are simulated in the anisotropic porous body approximation. The results from simulating the flow patterns of lead–bismuth eutectics in the experimental 19-rod assembly and water in a 61-rod nonheated assembly with its flow cross-section locally blocked in the central and corner parts are presented. The thermal–hydraulic processes in the BREST reactor fuel assembly’s heated 19-rod fragment with its flow cross-section locally blocked in the central part were also simulated using the CONV-3D DNS code in the framework of model cross-verification activities. The numerical analysis was carried out using the developed APMod software module implementing the anisotropic porous body model jointly with the integral turbulence model. It was demonstrated from a comparison of the numerical analysis results with both experimental data and simulation results obtained using the CONV-3D computer code that the APMod software module adequately describes the 3D fields of coolant velocities, pressure, and temperature arising in fuel rod assemblies with a locally blocked part of their flow section. The obtained results testify that the anisotropic porous body model can be used for simulating thermal–hydraulic processes in the cores and heat-transfer equipment of prospective reactors.