Interaction of Neptunium and Technetium with UO2+x

Interaction of uranium dioxide with highly mobile radionuclides Np-237 and Tc-99 was studied under oxidative conditions. Sorption of these radionuclides at different pH was measured, and the mechanism of redox reaction occurring in the course of their sorption were determined. In alkaline solution, Np(V) is reduced on the UO2+x surface and is sorbed in the form of tetravalent species. In neutral solutions, Np is sorbed in the form of Np( V). This is due to the fact that the stoichiometry of the UO2+x surface corresponds to U4O9. In acid solution, U(VI) is leached to form surface UO2. Although the free surface area of a UO2+x sample is low, the Np distribution coefficients K-d at pH > 6 are relatively high: logK(d) > 2. Unlike N-p, Tc(VII) is not reduced on the UO2+x surface. However, the sorption capacity of uranium dioxide for Tc(IV) is high.