First determination of dissolution rates of oriented UO2 single crystals

Millimetre UO2 single crystals were cut and oriented at JRC Karlsruhe. The orientation of each face of the parallelepiped single crystals was determined with Laue diffraction and the corresponding surface area by geometric measurements. Then, the (111), (100), (110) faces of each single crystal were polished to optical grade and characterized by XRD in order to confirm the surface orientation. The dissolution of the three single crystals was achieved in nitric acid media under dynamic conditions, at room temperature. Two dissolution regimes were observed for all samples. The normalized dissolution rate measured in the first step was not influenced by the crystallographic orientation of the faces. However, during the second step, (110) oriented faces were found to dissolve 4 times faster than the (100) faces. One explanation could involve the atomic composition of each oriented surface in the fluorite-type structure.