Multiphysics Simulation of TRISO Fuel Compacts and the Effects of Homogenization

TRistructural ISOtropic (TRISO) fuel particles are candidate fuels for High-Temperature Gas cooled Reactors (HTGRs) and many other advanced fission concepts due to their inherent safety features and high-temperature operation. Multiphysics modelling of a fuel compact with hundreds of thousands of TRISO particles (or more) is computationally challenging - not to mention the extension to a full-core model. Homogenization techniques are commonly used to model the heat conduction in the fuel compacts, which means representing the fuel compact as one material with effective thermal conductivity to reduce the computational cost. This work explores different approaches to model the multiphysics of the fuel compact including explicit modeling of TRISO particles and the homogeneous modeling. Different cases were considered for analysis to cover a wide range of TRISO packing fractions, total powers, and power densities. This analysis is performed with Cardinal, an open-source code that couples NekRS Computational Fluid Dynamics (CFD) and OpenMC Monte Carlo transport to the Multiphysics Object-Oriented Simulation Environment (MOOSE) for high-resolution multiphysics analyses of nuclear systems. The comparisons between the explicit and homogenized modelings approaches showed that the latter greatly underestimates the maximum and average temperatures within the TRISO particles. The error is highest for high TRISO power densities.