Coupling of neutronics, discrete element method, thermal-hydraulics and Voronoï mesh for pebble bed reactor analysis

The simulation of pebble bed reactors (PBRs) is often simplified using homogenized spectral zones, limiting the accuracy of key parameters such as power distribution, fuel burnup and temperatures. To address this, the hyper-fidelity tool (HxF) is extended to incorporate detailed thermal feedback by coupling the Monte Carlo code Serpent with the porous media solver GeN-Foam and a discrete element model (DEM). A novel Voronoï-based mesh mapping strategy is developed to enable efficient and accurate transfer of power density and temperature fields between the coupled solvers, capturing the strong spatial heterogeneities inherent to PBR cores. The methodology is applied to the HTR-10 reactor at equilibrium conditions. Results show that the proposed approach captures significant intra-core power variations, with pebble-wise powers deviating by up to ± 20 % compared to the isothermal model. In addition, the coupled model provides a prediction of the temperature distributions for the core components. The coupling framework enables consistent multi-physics feedback at the pebble scale and demonstrate that the proposed Voronoï-based coupling significantly enhances the fidelity of PBR simulations, providing a robust tool for core design, safety analysis, and fuel management.