Criticality Research on Plutonium

Based on the analyses of criticality data from recent experiments on homogeneous, hydrogeneous mixtures of Pu at an H/Pu ratio of 15, previously estimated curves for critical dimensions of homogeneous water moderated plutonium in the under moderated range have been revised significantly using transport calculations confirmed by the experiments. Curves of infinite cylinder diameters and slab thicknesses, sphere volumes, and masses, are presented for the concentration range from 0.1 to 10 kg/litre. Computed curves are given to show the effect of 240Pu on criticality, together with experimental data points at 2.2% and 8% 240Pu. Measured decay constants from pulsed neutron source and noise analysis experiments on critical and subcritical Pu systems are compared with computed values for H/Pu atomic ratios of 15-1068, An analysis of critical data on plutonium solutions has been made showing the effect of nitrate on criticality for reflected spheres with nitrate and plutonium concentrations extending to several hundred grams per litre. The results of a subcritical neutron interaction experiment performed with cans of dry PuO2 powder in a low density reflected cubic array are reported. The average density of PuO2 in the array was 1.16 g/cm3; the estimated critical mass was about 300 kg. (author)