A simplified heterogeneous Β1 model with isotropically-reflected neutrons on assembly boundary

Abstract

This model is based on the heterogeneous B1 theory and accounts for heterogeneous effects on the neutron streaming To the price of some approximations, it yields an iterative scheme to simultaneously compute the multi-group scalar fluxes and the directional currents in a heterogeneous geometry Although a similar simplified model called TIBERE, has already been proposed for specularly-reflected neutrons on the assembly (or cell) boundary there was a need to develop this new model, called TIBERE-2, for isotropically-reflected neutrons on the boundary This new model requires the classical and directional escape and transmission probabilities in addition to the classical and directional first flight collision probabilities calculated for an open assembly Consequently, considering the specific geometry of the CANDU reactor lattice, calculations with the TIBERE-2 model are as appropriate but less time consuming than those with the TIBERE model Moreover, this new model circumvents the divergence, leading to infinite leakage coefficients, appearing in the TIBERE model in the case when a PWR assembly is completely voided The TIBERE-2 model has been introduced, for 2D geometry, in the multigroup transport code DRAGON, in order to evaluate space-dependent leakage coefficients