The Role of Crystal Orientation in the Dissolution of UO$_2$ Thin Films

Epitaxial thin films have been utilised to investigate the radiolytic dissolution of uranium dioxide interfaces. Thin films of UO$_2$ deposited on single crystal yttria stabilised zirconia substrates have been exposed to water in the presence of a high flux, monochromatic, synchrotron x-ray source. In particular, this technique was applied to induce dissolution of three UO$_2$ thin films, grown along the principle UO$_2$ crystallographic orientations: (001), (110) and (111). Dissolution of each film was induced for 9 accumulative corrosion periods, totalling 270s, after which XRR spectra were recorded to observe the change in morphology of the films as a function of exposure time. While the (001) and (110) oriented films were found to corrode almost linearly and at comparable rates, the (111) film was found to be significantly more corrosion resistant, with no loss of UO$_2$ material being observed after the initial 90s corrosion period. These results distinctly show the effect of crystallographic orientation on the rate of x-ray induced UO$_2$ dissolution. This result may have important consequences for theoretical dissolution models, as it is evident that orientation dependence must be taken into consideration to obtain accurate predictions of the dissolution behaviour of UO$_2$.