Pulsed Reactivity Measurements of Large ²³⁵U-AI Castings in H₂O

Subcritical multiplication constants have been derived from pulsed-neutron measurements for 2×3 square pitch and hexagonal arrays of massive hollow cylinders of uranium-aluminum alloy in H₂O. The cylinders were 22.02-cm-o.d., 14.80-cm-i.d. bare ²³⁵U-Al alloy castings of 30.50 wt% uranium (76.97% ²³⁵U) in aluminum. These measurements extend previous benchmark experiments on similar castings with lower enrichments. KENO-IV, a multigroup Monte Carlo criticality code (with Hansen-Roach cross sections), calculates the subcritical multiplication constants for these lattices over the reactivity range 0.77 < k_eff < 0.98, with an average conservative bias of ∼0.005 in k_eff.