Numerical Simulation of Natural Convection Heat Transfer and Transport in Packed Beds: Mimicking a Proposed New Nuclear Fuel Design

The ability of coated particles of enriched uranium dioxide (UO₂) fuel to withstand high temperature and contain the fission products in the case of a loss of cooling event is a vital passive safety measures over traditional nuclear fuel active safety system to provide cooling. Hence, it is proposed in this study that Light Water Reactors (LWR) could be made safer by re-designing the fuel in the fuel assembly. A slender geometrical model with tube-to-particle diameter ratio N = 2.503 and porosity ε = 0.546 mimicking the proposed nuclear fuel in the cladding was numerically simulated. This is to investigate the heat transfer characteristics and flow distribution under buoyancy driven force expected in the cladding tube of the proposed nuclear fuel using a commercial code. Random packing of the particles is achieved by Discrete Element Method (DEM) simulation with the aid of Star CCM+. The temperature contour and velocity vector profile obtained can be said to be good illustration of anticipated heat transfer phenomenon to occur in the proposed fuel design. Similarly, heat transfer parameters such as particle-to-fluid heat transfer coefficient, Nusselt number, Grashof number and Rayleigh number were determined from simulated results and are presented. These parameters are of prime importance when analysing the heat transfer performance of a fixed bed reactor.