Investigating CAD-based Geometry Workflows for Multiphysics Fusion Problems Using OpenMC and MOOSE

Fusion system designs are complex and require intricate and accurate models that can be best represented using CAD-based geometry. In this study, we investigate the use of CAD-based geometry workflows in fusion systems multiphysics p roblems. Cardinal was used to couple OpenMC Monte Carlo transport to MOOSE heat transfer module. A simplified tokamak was introduced and modeled in CAD. The meshed geometry was prepared using direct accelerated geometry Monte Carlo (DAGMC) for particle transport, and a volumetric mesh was also prepared to be used in MOOSE’s finite element solver and to tally OpenMC results for heat source distribution and tritium production. Cardinal was used to run OpenMC Monte Carlo particle transport within MOOSE framework. The data transfer system transfered heat source and temperature distribution between OpenMC and MOOSE, with coupling between neutron transport and heat conduction achieved via Picard iteration. Two computational studies related to mesh refinement were p erformed: (A) refining the DAGMC and volumetric meshes used for tallying results and solving heat conduction (a “lockstep” refinement of all meshes used by all physics tools) and (B) only refining the DAGMC particle transport mesh (to investigate the impact of volume conservation in neutron transport). We demonstrate that multiphysics results could change as a result of either DAGMC model mesh not conserving the volume of the original CAD geometry, or a mismatch between the tally mesh and DAGMC particle transport mesh. Runtime studies also showed that, as expected, the refinement of the tally mesh has a much larger effect on the runtime compared to the refinement of the DAGMC particle transport surface mesh.