Head-end reprocessing studies of H.B. Robinson-2 fuel: II. Parametric voloxidation studies

A series of hot-cell tests was conducted with UO{sub 2} that had been irradiated to an average of 28,000 MWd/t in the H.B. Robinson-2 reactor of the Carolina Power and Light Company. The tests examined the effects of temperature and of the rate of oxygen supply on the release of gaseous and semivolatile fission products, while the fuel fragments were tumbled at 12 rpm during voloxidation - the high-temperature oxidation of UO{sub 2} to U{sub 3}O{sub 8}. The experiments showed that >99.9% of the tritium in the irradiated UO{sub 2} was released to the off-gas stream at temperatures of 480 and 550{sup 0}C and at oxygen feed rates ranging from 0.1 to 1.2 mol/h. The release of {sup 85}Kr varied from 2 to 7% of the fuel inventory. The U{sub 3}O{sub 8} product ({similar_to}99% smaller than 44 {mu}m) was easily dissolved in 7 M HNO{sub 3}. One 2-h leach in 7 M HNO{sub 3} dissolved {similar_to}99.5% of the heavy metals; a second 2-h leach in 7 M HNO{sub 3} brought the total to >99.98%. Voloxidation did not affect the final solubility of the uranium and plutonium but did increase the weight of the insoluble fission product residue from 0.18% of the irradiated UO{sub 2} to {similar_to}0.62%