Preliminary Analysis on Thermal-Hydraulic Behavior of PBR Cores Using DEM-CFD Coupled Method

Obtaining particle wise information of each PBR fuel would enhance accuracy in predictions for pebble locations, and pebble temperatures. However, the discrete modeling of thermal pebble behavior is complicated, and would take excessive computational time. Moreover, the packed state of PBR core, a pebble bed assembly may affect and be affected by the neutronic, thermal behavior of individual pebbles, leading to the need for a three-way coupling of mechanics, thermal hydraulics, and neutronics. In this study, a new DEM model has been developed to model interactions in packed bed systems in a mechanical, thermal point of view. A simplified radiative model was proposed, where the effective radiation range exhibited high accuracy for independent experiments at a value of 3.5rrpp. Moreover, a 4-mesh Finite Differential Scheme was applied to model internal conduction, and thermal expansion of fuels, which showed an error rate less than 7% compared to the analytical solution, while saving computational time. The DEM model was then coupled with a CFD code to simulate interactions in a solid-fluid two phase media. Where the results were compared with benchmark data of pressure drop and cooling in a packed pebble bed. Finally, a preliminary analysis was made for a PBR core by coupling a DEM/DEM-CFD with a neutronics code to obtain the temperature and packed state of the core based on the power distribution data. The feasibility of the DEM-Neutronic model was found sufficient, where further studies could be extended to the modeling of a more realistic PBR core.