Photochemical mutual separation technology between plutonium and neptunium in nitric acid solution

A photochemical method of removing Np from a mixture of nitric acid solutions of Pu and Np has been studied in connection with the Purex reprocessing procedure. The valencies and concentrations of Pu and Np in the initial samples were adjusted to Pu(III) and Np(V) and to 1x10-4 or 1x10-3 M (M=mol.dm-3), respectively. Experiments were carried out under various conditions by varying the irradiation rates of the Hg lamp and concentrations of HNO3. Under the conditions of an irradiation rate of 0.015 Watt (W), a 3 N HNO3 solution containing reductants and a Pu concentration of 1x10-4 M, the initial valence of Pu(III) was rapidly oxidized to Pu(IV), and more than 95% of Pu(IV) remained at the same valence even after continuous irradiation. On the other hand, Np(V) did not change. These valences, Pu(III) and Np(V), are optimum for separating Np from Pu using TBP-n-dodecane extraction. These results lead to the conclusion that the photochemical valence adjustment has a high potential for removing Np from a Pu and Np mixed solution and for re-oxidation process technology instead of the conventional process using NOx gas. Furthermore, the photochemical reaction mechanism of Pu and Np was discussed from the standpoint of thermodynamic considerations, and then the applicability of this photochemical technology in a reprocessing process was discussed based on the experimental data obtained in this work. (orig.)