A preliminary study on numerical simulation of pebble flow in pebble-bed nuclear reactor

The flow profile of graphite fuel pebbles in pebble bed high temperature reactor (PBR) lays the foundation for core physical design and is closely relevant to reactor physics, thermal-hydraulics and fuel cycle, consequently influencing reactor safety and economical efficiency. However for the complexity of dense slow pebble flow and the limited information obtained from experiment, it is necessary to further study pebble flow with the approach of numerical simulation, one of the proper methods is kinematic model which is based on the continuous diffusion theory for dense slow flow. This paper generates numerical pebble flow velocity profile with the kinematic model in transformed Cartesian coordinates. Two treatment scheme, central difference method and second-order accurate forward or backward difference method, are adopted to discretize the diffusion equation and corresponding boundary conditions in reactor geometry. The simulated relative flow velocity profile of core geometry from a referenced paper agrees well with the experimental results in the referenced paper. Besides, numerical simulation of velocity profiles in a real HTR-PM geometry is studied to obtain more information on flow features in different core regions. (authors)