Precipitation behavior of Pu and other transuranium elements with a combustible organic reagent Ncyclohexyl-2-pyrrolidone (NCP) has been examined to develop a simple reprocessing process of spent nuclear fuel based only on precipitation method. Experiments on the precipitation behavior of Pu in HNO 3 solution containing only Pu showed that both Pu(VI) and Pu(IV) were precipitated with NCP, but they required more NCP than in the U(VI) precipitation. Selective U(VI) precipitation from HNO 3 solution containing U(VI) and Pu(IV) (U(VI)-Pu(IV) solution) was achieved by stirring the solution for sufficient time after addition of NCP with ratio of [NCP]/[U] = 1.4. Addition of an enough amount of NCP to U(VI)-Pu(VI) or U(VI)-Pu(IV) solutions gave a quantitative precipitation of both U and Pu. From a viewpoint of the physical property of the precipitate, Pu(VI) was found to be favorable for the U-Pu precipitation. Hence, we have studied the oxidation of Pu(IV) to Pu(VI). As a result, heating of the solution was found to be a promising method for the present process. Furthermore, it was clarified that neither Am(III) nor Np(V) was precipitated in the selective U precipitation and the simultaneous U-Pu precipitation. These results demonstrate the feasibility of the reprocessing by precipitation with NCP.
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