CONIFERS - A Reactor Core Analysis Program with Emphasis on Reactors with Channels

Abstract

CONIFERS is a reactor core analysis program. Its main special feature is that it offers the option of solving either the conventional finite-element diffusion equation or a neutron-balance equation that is particularly intended for nuclear reactors whose fuel is in channels that are separated from each other by several neutron mean-free-path lengths of moderator. Different parts of the core can be represented by different options. The purpose of the channel-oriented option is to improve the accuracy when adjacent channels contain strongly different fuel bundles, so that a cell coders modelling of the cell's environment is inaccurate. In the channel-oriented option, CONIFERS characterizes the neutron flux distribution in the core by means of one number per cell per energy group, as in the conventional finite-difference procedure, but the transverse leakage and the reaction rates are calculated according to a formula based on the use of boundary conditions on the channel surface that are derived from the reaction rates, itemized by group number, and the average macroscopic cross sections in the moderator that are calculated by the cell code. Other features of CONIFERS are that: Its geometry is particularly flexible, It can handle a wide variety of reactivity scales, including ones that are based on adjustments of reactivity devices, and can handle several at once. As a further contribution to flexibility, CONIFERS is in the form of a set of subroutines. Although CONIFERS offers the option of mixing the channel-oriented and the finite-difference representations in one core, serious disagreement with experiment occurs in the interfacing. Until this problem has been solved, it will not be possible to test accurately the efficacy of the channel-oriented equation in calculating the behaviour of cores with great difference between adjacent channels.