Study on Nuclear Fuel Reprocessing Using Photochemical Reactions

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In the nuclear fuel reprocessing, interest has been focused on the recovery of transuranium elements, such as Pu, Np, Am and Cm, because of their hazardous radioactive neture. In order to recover these transuranium elements, the valence adjustments are of primary importance. For example, in the Purex method using tributylphosphate (TBP) as an extracting reagent, Pu(VI), Pu(IV) and Np(VI) are extracted to the organic phase with U(VI), but Pu(III) and Np(V) remain in the aqueous phase. Am(VI) is also extracted to the organic phase, if oxidized by a strong oxidant.In the present study, a photochemical method of adjusting the oxidation states of actinide ions has been investigated. It was found that the irradiation of high pressure mercury lamp to the nitric acid solution containing Pu^3+ and NpO_2+ oxidized only Pu^3+ to Pu^4+ keeping NpO_2+ at pentavalent ion under suitable irradiation conditions. Therefore, the selective extraction of Pu is possible from the solution containing Pu and Np. Under the irradiation of high intensity of light in the similar solution described above, both Pu and Np were oxidized to hexa-valent ions, MO_2^2+. This means that both Pu and Np are extracted to the organic phase and it was confirmed by extraction experiments. On the other hand, in the irradiation of the organic solution containing Pu(VI) and Np(VI) ions, resulted in the back extraction of Np to the aqueous phase accompanied by the photo-reaction of Np(VI) to Np(V).