PROCESS FOR THE FINE PURIFICATION, BY LOTS, OF URANIUM OR PLUTONIUM WHICH MUST BE RECOVERED IN AN OPERATION FOR THE PROCESSING OF NUCLEAR FUELS AND / OR IRRADIATED FERTILE MATERIALS

摘要

Process for the batch purification of uranium recovered in a reprocessing process, after a first separation of impurities, in which for each batch an aqueous, nitric acid uranyl-nitrate solution (UNH original solution), which still contains residual amounts of impurities, is cooled to crystallize out purified UO2(NO3)2x6H2O (UNH) from the solution and the resulting crystals are separated out of their mother liquor and washed. The original solution is adjusted to a specified uranium concentration and the adjusted solution is cooled to below 0 DEG C. to bring about the crystallization. The duration between starting and ending the crystallization is held between 0.1 and 10 hours. The amount of the UNH crystals which is crystallized out corresponds to at least about 80 weight % of the uranium content introduced. The ratio of the volume of the crystals formed to the volume of the remaining mother liquor is not larger than 0.5. A final concentration of nitric acid is estabilished in the mother liquor between 6 and 12 mol/l HNO3 at room temperature. A joint crystallizing out of UNH with water as ice and/or with nitric acid trihydrate (HNO3x 3H2O) is avoided. The resulting mother liquor is separated from the crystals and then recycled. The separated crystals are washed at least one time with an HNO3 solution having a similar acid content and similar temperature to that of the separated mother liquor at the end of the crystallization procedure. A batch process for purifying plutonium or plutonium and uranium is also disclosed.