Study on Nuclear Fuel Reprocessing Using Photochemical Reactions

在核燃料后处理中，由于钚、Np、Am和Cm等超铀元素具有危险的放射性，其回收一直是人们关注的焦点。为了回收这些超铀元素，价调整是最重要的。例如，在以磷酸三丁酯（TBP）为萃取剂的Purex法中，Pu（VI）、Pu（IV）和Np（VI）与U（VI）一起被萃取到有机相中，而Pu（III）和Np(V)则留在水相中。如果被强氧化剂氧化，Am（VI）也被萃取到有机相。本文研究了一种调节锕系离子氧化态的光化学方法。发现高压汞灯在适当的照射条件下，将Pu^3+和NpO_2+的硝酸溶液中，只将Pu^3+氧化为Pu^4+，并使NpO_2+保持在五价离子状态。因此，从含有Pu和Np的溶液中选择性地提取Pu是可能的。在上述类似溶液的强光照射下，Pu和Np都被氧化成六价离子MO_2^2+。这意味着Pu和Np都被萃取到有机相，并通过萃取实验得到了证实。另一方面，在含有Pu（VI）和Np（VI）离子的有机溶液的照射下，Np被反萃取到水相中，同时Np（VI）与Np(V)发生光反应。

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).