Effect of ruthenium metallic particles on the kinetics of dissolution of UO2 in nitric acid.

Abstract : UO2 pellets containing 3 mol. % of Ru were prepared then characterized. The speciation, the morphology and the spatial distribution of Ru in the sintered samples were determined. These samples were submitted to dissolution tests in nitric and hydrochloric acids, as well as UO2 pellets in the presence and in absence of Ru-metal particles in solution. The evolution of the elemental concentrations in solution was followed, then the residues of dissolution were characterized. The presence of metallic particles of Ru incorporated in the pellet increased significantly the dissolution rate of UO2, both in nitric and hydrochloric media. A mechanism was then proposed to explain their influence on the kinetics of dissolution of UO2 in nitric acid solutions.