Summary of criticality data obtained at Battelle Pacific Northwest Laboratories on fixed and soluble poisons in U + Pu nitrate solutions

Knowledge of the effects of neutron poisons on U +Pu systems is necessary to better establish criticality safety programs. These data are needed in setting of criticality safety specifications for storage, processing and shipping of fissile material where it is desired to handle larger quantities with safety and efficiency. These data are needed also for validating calculational techniques and cross sections sets. U + Pu solutions containing 30% Pu in the total U + Pu were used in these experiments to determine the effect of neutron poisons. Criticality of heterogeneous systems of UO2-PuO2 rods in a lattice were studied when the U + Pu solutions with various amounts of Gd and + B were added to the system. Criticality of homogeneous systems of the U + Pu nitrate were determined with varying amounts of Gd and Gd + B added to the solution. Measurements were made to determine also the effect of boron-glass raschig rings on the criticality of the U + Pu nitrate solution systems