Analysis of plate latticce heterogeneity effects of fast reactor with coarse group constants

An advanced method has been developed to analyze the heterogeneity effect of a multi-region plate lattice system accurately enough with the coarse group constants. This treatment is characterized by the modification brought to effective admixture cross sections and correction on elastic removal cross sections. The mutual interference among different plates are taken into account in determining the admixture cross sections. The effective cross sections thus obtained agree well with the results obtained by ultra fine spectrum codes. The elastic removal cross sections of light nuclides are corrected near the sodium resonance by means of a simple analytical expression for the flux depression. With this correction remarkable improvement was observed in the flux heterogeneity. In solving the multi-group transport equation for flux heterogeneity, the fission source iteration was found to be dispensable under most conditions. (auth.)