Development of a simple reprocessing process using selective precipitant for uranyl ions. Precipitation behaviors of plutonium and other transuranium elements

Precipitation behaviors of Pu and other transuranium elements with N-cyclohexyl-2-pyrrolidone (NCP) have been examined to develop a simple reprocessing process of spent nuclear fuel based only on precipitation method. It has been already found that a combustible organic reagent, NCP, can selectively precipitate UO22+ ions in aqueous HNO3 solutions. Experiments on the precipitation behavior of Pu in HNO3 solution containing only Pu showed that both Pu(VI) and Pu(VI) were precipitated with NCP, but they required more NCP than in U(VI) precipitation. It was found that selective U precipitation from U(VI)-Pu(IV) solution was possible by stirring the solution for sufficient time after addition of NCP with ratio of [NCP]/[U]=1.4. Addition of enough amount of NCP to U(VI)/P(VI) or U(VI)-P(IV) solutions gave a quantitative precipitation of both U and Pu. These results demonstrate the feasibility of the reprocessing by precipitation with NCP. (author)