Voronoï Mesh for a Thermally Coupled Model of Pebble Bed Reactor

Hyper-fidelity depletion (HxF) is a novel approach to depletion of a pebble bed reactors (PBRs) that allows to track fuel composition and trajectory of each pebble individually.Currently, HxF assumes a uniform temperature distribution in the core; therefore, this study aims to evaluate the impact of using an accurate temperature distribution for representing the equilibrium state of PBR versus using a uniform temperature model.HxF coupled with DEM (Discrete Element Model) was used to perform depletion up to equilibrium for the gas-cooled PBR HTR-10.An iterative Serpent-GeN-Foam coupled model was then applied to determine the spatial temperature distributions for all core components.In order to leverage the individual pebble data that HxF can provide, the coupling was built based on two different meshes.A coarser Voronoï mesh was used for the neutronics with each cell corresponding to a pebble and a finer mesh was used for the thermal-hydraulic model.In addition to the large temperature swing that is to be expected for gas-cooled reactors, the results for the coupled model show up to ~30% change in local power when compared to the uniform temperature model.Additional important information regarding the thermal-hydraulic behavior of the core were obtained, especially regarding the velocity of the coolant and the flow direction.In particular, the results show that the main vector driving the temperature of the fuel is the coolant temperature.