Dissolution behavior of pulverized irradiated fuels in nitric acid solutions

In order to examine the dissolution behavior of pulverized irradiated fuels, approximately 1g of powdery irradiated fuels (burnup: 50 GWd/t, cooling time: more than 15 yr, size: 90-150, 300-355, and 850-1,000 mu m) was weighed out accurately and dissolved in HNO3 solutions (300 cm(3)) stirred at 300 rpm. The dissolution reactions were followed by measuring [UO22+] and [HNO2] in dissolvent solutions. Dissolution ratios were calculated as percentage of [weight of uranium dissolved]/[initial weight of uranium in fuels]. It was found that the powdery irradiated fuels are dissolved easily even at room temperature in 3-4 M (mol/dm(3)) HNO3 solutions and much more rapidly than non-irradiated UO2 powders (95% theoretical density). These results indicate that the pulverization of irradiated fuels is effective for malting the dissolution conditions mild. Furthermore, the difference in dissolution behavior between powdery non- and irradiated fuels were suggested to he due to the difference in their densities, the acceleration effect of certain fission products in irradiated fuels, or the participation of oxidants other than HNO2 and NO3- in dissolution reactions of irradiated fuels.