A Notable Comparison of Computational Geometries in MCNP6 Calculations

MCNP6 has been extended to include a new capability that permits tracking of neutrons and photons on an unstructured mesh (UM) embedded as a mesh universe within its constructive solid geometry capability. Our mesh geometry was created through Abaqus/CAE using its solid modeling capabilities. Monte Carlo transport results are calculated for mesh elements using a path length estimator while particles track from element face to element face on the mesh. This paper presents some performance comparisons for the initialization and calculation phases of two well-known benchmark problems using both the legacy and the UM tracking capabilities. For detailed geometries, UM initialization is always faster. For very detailed geometries where the models are comparable, the UM capability is faster than the legacy geometry capability.