An Analysis of Selected Fast Critical Assemblies Using ENDF/B-IV Neutron Cross Sections

Measured integral quantities such as k_eff, central reaction-rate ratios, and central reactivity coefficients for 18 fast critical assemblies were calculated using the ENDF/B-IV neutron cross-section set. The correlations between calculation and experiment using Version IV were then compared to those obtained with earlier cross-section data, specifically, Versions I, II, and III of ENDF/B and the Bondarenko cross-section set. In general, ENDF/B-IV was found to do an excellent job of calculating k_eff. However, discrepancies between calculation and experiment did exist for both reaction-rate ratios and reactivity coefficients. Of particular interest, the fissile-fuel central-worth discrepancy for plutonium assemblies was found to be ∼20%.