Criticality of Plutonium-Uranium Mixtures Containing 5 to 8 wt% Plutonium

Results are presented from a series of criticality experiments with homogeneous plutonium-uranium fuel mixtures with plutonium content in the range of 5 to 8 wt%. The H:(Pu+U) atomic ratios covered a range from 19.5 to a high of 80.7: the experiments provide data in the region of moderation where the minimum critical volume occurs for homogeneous plutonium-uranium systems with a plutonium content of 8 wt%. The minimum critical spherical radius for material containing 8 wt% Pu in PuO₂-UO₂-water mixtures was determined to be 14.98 cm., The criticality factors were computed with neutron transport theory and Monte Carlo calculations, using the DTF-IV and the KENO-II codes with both ENDF/B-II and ENDF/B-III version cross sections. The calculated values were found to be within ±2% of unity.