Numerical Investigation of Flow in Generation IV Pebble Bed Gas Cooled Core Reactors

This article presents a numerical investigation of thermal-fluid dynamics processes through the gaps of the spherical fuel elements (fuel pebbles) in the core of a Pebble Bed Reactor (PBR), using Computational Fluid Dynamics (CFD). The PBR is one of the most promising projects of the six classes of Generation IV Very High Temperature Reactor (VHTR). The results of two analyzes are presented. In the first case were evaluated two models of heat transfer to the spherical fuel. In this model is specified the volumetric heat generation, with thermal conduction in the fuel, and in the cladding. In the second model was specified a particular heat flux at the spherical fuel elements surface. In this analysis were performed simulations in two arrays of spheres i.e., the spheres into contact and spaced 2 mm. In the second analysis was also evaluated the influence of the spheres arrangement in the bed thermal-fluid dynamic behavior. The set of pebbles that constitute the core was modeled by representations of crystalline structure with different packing factors. The four simulations of the first analysis showed differences in flow and temperature profiles and maximum surface coating. There were also no significant differences in flow and heat transfer between the beads and the fluid in cases with different packing factors. These results show the importance of simulation of heat conduction inside the pebble fuel as well as the need to better assess the influence of the arrangement formed by pebbles fuel in PBR reactors thermal-fluid dynamics behavior.