The development of an accident tolerant nuclear fuel for water-cooled reactors would re-defined the status of these reactors from traditional active safety to passive safety systems. As a possible solution towards enhancing the safety of light-water reactors (LWRs), loose-coated particles of enriched uranium dioxide fuel with the ability to retain gaseous and metallic fission products in the case of a loss of cooling event can be introduced inside Silicon-Carbide cladding tubes of the fuel assembly (see Fig.1a & b). These coated particles are treated as a bed from where heat is transferred to the cladding tube and helium gas movement is due to natural convection. A slender geometrical model with tube-to-particle diameter ratio N = 2.503 and porosity e = 0.546 mimicking the proposed nuclear fuel in the cladding was simulated. This study investigates 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 particles is achieved by Discrete Element Method simulation. The temperature contours and velocity vector plots obtained can be said to be good illustration of anticipated heat transfer and transport phenomenon envisaged in the proposed fuel design. Simulated results for particle-to-fluid heat transfer coefficient, Nusselt number,and Rayleigh number which are of prime importance when analyzing natural convection heat transfer performance in fixed bed reactors were validated. Results obtained are in close agreement with established numerical and experimental works.