Abstract UO 2 pellets incorporating 3 mol.% of Ru was prepared by using a wet chemistry route and then characterised. The speciation, morphology, as well as spatial distribution of Ru in the sintered samples, were determined. The synthesised samples were submitted to dissolution tests in 0.1 M nitric acid at 60 °C and the dissolution of pure UO 2 pellets was also studied with and without the presence of Ru metallic particles in the solution. The evolution of the U, Ru, and nitrous acid concentrations in solution was measured and the residues of dissolution were further characterised. The obtained results unambiguously demonstrated the catalytic activity of Ru-metal particles during UO 2 dissolution in nitric acid provided that a solid/solid interface existed between UO 2 and Ru-metal particles. This positive impact on the dissolution kinetics of UO 2 was supported by redox reactions taking place at both nitric acid solution/Ru-metal particles and at Ru-metal particles/UO 2 interfaces.