A comparison of Monte Carlo methods for neutron leakage at assembly level

The treatment of neutron leakage at assembly level is an essential step in the generation of few-group cross section data for reactor calculations. This work compares methods used for the characterization of assembly leakage in the framework of Monte Carlo cross section generation, using nearly-critical colorset configurations in order to obtain approximate reference values. The B1 fundamental mode approximation and the albedo-search method are compared in terms of eigenvalue, multi-group homogeneous scalar fluxes and maximum pin power differences for several cell types. The performance of a novel heterogeneous leakage method is also tested. Whereas B1 corrections provide the best agreement in homogeneous fluxes, the new method furnishes the best consistence in terms of pin powers, whilst providing rich spectral information and reducing computational overheads associated with colorset calculations. Future investigations are suggested in order to test the performance of these methods in the calculation of few-group, leakage-corrected assembly cross sections and discontinuity factors.