Uranium dioxide interaction with groundwater - Leaching behavior and sorption tests

The solubility of three UO2 samples that were synthesized at different temperatures in reducing atmosphere and having different composition of surface oxidized layer was studied in distilled water and tuff groundwater (J-13). The solubility of the samples was governed by the presence of U(VI) in the surface oxidized layer. The sorption of Np(V) on those samples was accompanied by its partial reduction upon contact with UO2 (samples). For Np(IV) a partial oxidation was observed at pH values between 4.5 and 6.5. The most oxidized sample, with the highest U(VI) content in the surface layer, despite the highest solubility, was more efficient in the sorption of Np(V).