Lattice physics codes comparisons for the NEA BWR-MOX benchmark - 098

This work presents the comparison of the results obtained with three different lattice physics codes (HELIOS, CPM-3 and MCNP-4B) for the Nuclear Energy Agency (NEA/OECD) benchmark of a Boiling Water Reactor (BWR) assembly using uranium - plutonium mixed oxide fuel (MOX). The objective of the work is to compare the performance of different state of the art transport codes based on different methodologies. The benchmark considers an advanced 10 X 10 BWR fuel assembly with a square central channel in the place of nine fuel rods and five rods with Gd₂O₃ as burnable absorber. The results show some differences in the neutron multiplication factor between the three codes due to the difference of the method of solution and the difference of their neutron energy group structure. A consistent trend is observed in the difference of the neutron multiplication factor between HELIOS and CPM-3 related to MCNP-4B, as the void percentage increases. A sensitivity study on the energy group structure shows the importance of the choice of the energy discretization in the multigroup calculations in MOX lattices. The maps of local fission rates show a quite good agreement between the codes; comparable to the differences obtained for UO₂ assemblies. Finally the results obtained in the burn-up calculations show a good agreement between HELIOS and CPM-3. (author)