Effect of Fixed and Soluble Neutron Absorbers on the Criticality of Uranium-Plutonium Systems

Knowledge of the effects of neutron absorbers on the criticality of uranium-plutonium systems is necessary to better establish criticality safety programs. These data are needed in setting criticality safety specifications for storage, processing, and shipping of fissile materials where it is desired to handle quantities with safety and efficiency. These data are also needed for validating calculational techniques and cross-section sets. Aqueous solutions of the nitrates of uranium and plutonium were used in these experiments to determine the effect of neutron absorbers on criticality. In some experiments, UO2 and PuO2 rods were latticed in the solutions to which various amounts of gadolinium and a gadolinium-boron mixture were added. Critical dimensions were measured of homogeneous mixtures of the solutions with varying amounts of gadolinium and gadolinium-boron added. The effect of boron-glass Raschig rings on the criticality of the solutions was also determined. Plutonium comprised 30 wt% of the uranium-plutonium component of the solution.