Analysis of the structure of layers on UO2 leached in H2O

A brief description is given on nuclear techniques (Rutherford backscattering/channeling, resonance scattering and elastic recoil detection analysis using energetic He-ions) used in the analysis of surfaces of UO2 single crystals leached in demineralized water with different pH-values at temperatures up to 200 degrees C. The rate-law for layer-growth and the composition of the layers formed on UO2 depended on T and pH-value. For temperatures between 150 and 200 degrees C and pH in the range 6 to 10, a t(1/2)-law was found for growth of U3O7 layers; the deduced activation enthalpy of 0.7 +/- 0.1 eV is compatible with rate-controlling diffusion of oxygen-interstitials through the leach layers, These were water-foe and retained some coherence with the UO2. A thin (similar to 5 nm) distorted transition layer was formed between the UO2 and the U3O7 accommodating most of the misfit.