Uncertainty in the Breeding Ratio of a Large Liquid-Metal Fast Breeder Reactor: Theory and Results

Abstract

Using an extensive data base of sensitivities and evaluated covariances, this work incorporates 11 fast-reactor benchmark experiments and 2 neutron-field benchmark experiments into the adjustment of a 26-group cross-section library based primarily on Evaluated Nuclear Data File (ENDF)/B-IV. The covariance data include correlations between cross sections for different energies, reactions, and materials, and between integral experiments, and covariances of calculational bias factors due to specific modeling and calculational procedures. The adjustments of the group cross sections are examined in some detail and are smaller than the estimated standard deviations. The results of the adjustment are applied to the determination of the uncertainties in the multiplication factor and in the breeding ratio of a large liquid-metal fast breeder reactor design model fixed by the Large Core Code Evaluation Working Group. For this static model the adjustment procedure reduces the calculated uncertainty in keff from 3.1% to 0.5% and in breeding ratio for the critical reactor from 3.5% to 1.9%.