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 t ime: more than 15 yr, size: 90-150, 300-355, and 850-1,000 mu m) was weighe d out accurately and dissolved in HNO3 solutions (300 cm(3)) stirred at 300 rpm. The dissolution reactions were followed by measuring [UO22+] and [HNO 2] in dissolvent solutions. Dissolution ratios were calculated as percentag e of [weight of uranium dissolved]/[initial weight of uranium in fuels]. It was found that the powdery irradiated fuels are dissolved easily even at r oom temperature in 3-4 M (mol/dm(3)) HNO3 solutions and much more rapidly t han non-irradiated UO2 powders (95% theoretical density). These results ind icate that the pulverization of irradiated fuels is effective for malting t he 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 f ission products in irradiated fuels, or the participation of oxidants other than HNO2 and NO3- in dissolution reactions of irradiated fuels.