Investigating fission distribution behavior under various homogenization techniques for asymmetrical fuel assemblies and different reflector equivalence methods

Abstract

This article provides an analysis of the impact of asymmetrical assemblies homogenization and reflector modeling methods over the fission distribution, based on the first startup of the BEAVRS benchmark v2.0.2, in Hot Zero Power state (HZP). We use a classical two-step simulation with the deterministic codes DRAGON5 and DONJON5. First a transport calculation is performed with DRAGON5 on fuel assemblies, based on previous work conducted at the Polytechnique Montréal. Then, the complete core calculation is done with DONJON5 using a two-group energy mesh, in diffusion theory. The fission rates are calculated using DONJON5 and compared to the in-core detectors data provided in the BEAVRS benchmark. Discrepancies between the simulation and radial adjusted measurements present a Root Mean Square error (RMS) discrepancy of ≃4.5% (with relative errors lower than 10%). The results show the necessity to consider heterogeneity when it comes to model assemblies without central symmetry.