Effect of surface orientation on dissolution rate and surface dynamics of UO₂ single crystals in nitric acid

UO₂ single crystals with (100) (110) and (111) oriented faces were dissolved in 2 mol.L^-1 HNO₃ at room temperature. The evolution of the topography of the surface was monitored and reliable dissolution rates corresponding to the three crystallographic orientations were determined under controlled hydrodynamic and chemical conditions. The dissolution tests of UO₂ polished single crystals showed two different kinetic steps. During the first uncatalyzed kinetic regime, the enhanced reactivity of the surface at defect sites was demonstrated. The second kinetic step was attributed to a catalysed dissolution mechanism involving species produced at the solid/solution interface during the first step. (authors)