A hybrid continuous energy and multi-group Monte Carlo method

Abstract

This paper investigates mixing multi-group (MG) and continuous energy (CE) representation of cross-sections depending on location of a particle in a Monte Carlo neutronic eigenvalue calculations in 1D and 2D PWR test cases with UOX and MOX fuel. Different population normalisation needs to be applied to CE and MG region to account for the difference in criticality between CE and MG representation. This normalisation procedure requires a neutron production rate ratio between CE and MG region to be known a priori. A resonance correction in energy spectrum during transition of a particle between the MG and CE region was developed based on the equivalence resonance treatment theory. With these, it was shown that it is possible to accelerate total calculation time, while introducing only a moderate error below 1% in the fission rate distribution. The magnitude of acceleration is heavily dependent on the relative size of CE and MG zones.