Pretreatment of Hanford medium-curie wastes by fractional crystallization

Acceleration of the schedule for decontamination of the Hanford site using bulk vitrification requires implementation of a pretreatment operation. Medium-curie waste must be separated into two fractions: one is to go to a waste treatment and immobilization plant and a second, which is low-activity waste, is to be processed by bulk vitrification. The work described here reports research on using fractional crystallization for that pretreatment. Sodium salts are crystallized by evaporation of water from solutions simulating those removed from single-shell tanks, while leaving cesium in solution. The crystalline products are then recovered and qualified as low-activity waste, which is suitable upon redissolution for processing by bulk vitrification. The experimental program used semibatch operation in which a feed solution was continuously added to maintain a constant level in the crystallizer while evaporating water. The slurry recovered at the end of a run was filtered to recover product crystals, which were then analyzed to determine their composition. The results demonstrated that targets on cesium separation from the solids, fractional recovery of sodium salts, and sulfate content of the recovered salts can be achieved by the process tested.