Critical Three-Dimensional Arrays of U(93.2)-Metal Cylinders

Criticality studies were made of three-dimensional arrays of uranium-metal cylinders enriched to 93.2 wt% in ²³⁵U. Four weight groups of units, ranging from 10.4 to 26.2 kg of uranium in five geometries, were employed to determine the critical surface separation between units as a function of the number in an array. The influence on criticality of hydrogenous neutron reflecting and moderating materials, unit shape, array shape, and of other controlled perturbations to some assemblies was examined. Monte Carlo calculations were performed of the experimental assemblies to confirm the neutron multiplication factors and to interpret the behavior of several subcritical assemblies. The Hansen-Roach neutron cross-section sets reproduce the results of the experiments, in a majority of cases, to an accuracy of ≈1% in k_eff.