Study on radiation-induced oxide-reduction of actinoid ions in acid solution

Many studies have been made on the application of actinoid ion, especially UO22+ to change atomic valance but the mechanism of photoreduction has not yet been solved. In this study, the mechanism of photoreduction of UO22+ in acid solution was investigated. As functions of alcohol and acid concentrations, φ(UIV) was determined and photoreduction of UO22+ was investigated as well as NpO22+. As an increase of alcohol content (EtOH, MtOH, iso-PrOH), φ(UIV) increased to reach a plateau (∼0.6). In addition, φ(UIV) increased linearly with an increase of acid content and the value became smaller in the order, H3PO4, H2SO4, HClO4 solution. Comparing with these results of UO22+, photoreduction of NpO22+ was investigated. Only NpO2+ was produced as the final products, but not NpIV and NPIII. Alcohol dependency of NpO22+ photoreduction was similar to that of UO22+ system but the plateau level of φ (NpO22+) was lower (∼0.15) than the latter. (M.N.)