Improved gamma-heating calculational methods for fast reactors and their validation for plutonium-burning configurations

A new calculational scheme has been developed for the accurate assessment o f gamma heating in fast reactors, its special feature being the determinati on of the gamma source distribution that is formulated in a near-to-exact m anner. The improved methodology, which has been implemented into the ERANOS (European Reactor Analysis Optimized System) code package, is currently va lidated for Puburning configurations, for which gamma-heating target accura cies are particularly high. This has been accomplished through comparisons with new integral measurements conducted at the MASURCA facility, as well a s with reevaluated earlier experiments. In the new measurements, absolute g amma-heating rates were determined in PuO2/UO2-fueled cores surrounded by a steel/sodium reflector mainly using TLD-700 thermoluminescent dosimeters. Thereby, a considerable effort was undertaken to minimize systematic errors . The calculation/experiment values determined from the analysis of the cri tical experiments are 0.90 for the PuO2/UO2 core region, 0.84 for the steel /sodium reflector, and 0.89 for an internal steel/sodium diluent zone. The most plausible causes for the observed discrepancies have been identified t o be data related, i.e., too low fission gamma energies and too low capture cross sections for the structural elements. The transferability of the cur rent validation findings to a modified Superphenix configuration, in which the radial fertile blanket is replaced by a steel/sodium reflector, and to the 1500 MW(electric) Pu-burning CAPRA 4/94 reference design has been demon strated.