Book Description

A process scheme for the recovery of uranium from fuel elements has been developed. The scheme combines continuous fluid-bed drying and fluoride volatility techniques after initial dissolution of the fuel element in the appropriate aqueous system, hence the designation ADF, Aqueous Dry Fluorination Process. The application of this process to the recovery of uranium from highly enriched, low uranium-zirconium alloy plate-type fuels is described. ln the process, the feed solution is sprayed horizontally through a two-fluid nozzle and is atomized directly in the heated fluidized bed. The spray droplets are dried on the fluidized particles and form a dense coating. Excessive particle growth was limited by the use of air attrition-jets inserted directly in the bed. Aqueous hydrofluoric acid solutions containing leaves2 to 3.6 M zirconiuni, 0.007 to 0.03 M uranium, and free acid concentrations from 1 to about l0 M were successfully processed in a 6-in.-diameter Inconel fluid-bed spray dryer. Rates equivalent to about 3.l kg/hr of zirconium were achieved, 160 ml/min with the most concentrated feed solution. Experiments were successfully carried out from 240 to 450 deg C.A new design for a two-fluid nozzle was developed. Extensive work was done to identify the various zirconium fluoride compounds formed. The granular dryer product was subsequently fluorinated at temperatures to 600 deg C in fluid beds and to 700 deg C in static beds to remove the uranium as the volatile hexafluoride. About 90 to 95% uranium removal was consistently achieved near 600 deg C. The relatively low uranium recovery under these conditions is a disadvantage for the application to zirconium-base fuels. It was found necessary to resort to static beds and higher temperatures to achieve greater removal. Since the fluorine attack on nickel, the material of construction, is prohibitive at temperatures above 600 deg C, a disposable fluorinator concept for use with static beds is described. Results of corrosion studies are reported. A preliminary chemical flowsheet with a design capacity of 1l00 kg of uranium (93% enriched) annually is presented. (auth).