Tibere and Tibere-2: new consistent models for calculation of space-dependent directional leakage coefficients for a heterogenous assembly

Abstract

The influence of nuclear reactor core lattice heterogeneity on neutron leakage has been taken into account by two leakage models named TIBERE and TIBERE-2 These models are founded on the heterogenous Bn theory, that the existence of a fundamental mode in an infinite and regular lattice of identical assemblies of cells, thus enabling that the macroscopic flux, which is periodic and describes fine variations in a perfectly reflected assembly or cell The reason why the simplified heterogenous B1 models TIBERE and TIBERE-2 have been derived is to consider the streaming anisotropy and heterogeneity within a fine flux transport calculation in a consistent manner since the homogenous B1 leakage model is insufficient, especially in cases when a reactor itself or certain reactor assemblies (or cells) contain voided zones or zones with low density media, ie, zones with a long mean free path, so that the streaming effect may become important They use numerical solution methods already existing in available neutron transport codes, without increasing considerably computing time compared to ordinary calculations of multigroup flux maps (author)