Impact of platinum group metals (Ru, Pd, Rh) on the dissolution of UO2

The effect of metallic particles containing Platinum Group Metal (PGM) elements on the dissolution of sintered UO2 samples was examined through the development of multiparametric dissolution tests on sintered UO2 and UO2 + 3 mol.% PGM samples. This effect was found to be more important for CHNO3 < 1 mol L−1 whereas it was lowered for higher nitric acid concentrations due to the preponderant oxidation of U(IV) by nitrate ions. Increase of the normalised dissolution rate of the ceramics was associated to the presence of PGM elements along with the decrease of the duration of the induction period (the stronger effect being observed for ruthenium). Simultaneously, the decrease of the apparent activation energy associated to the reaction of dissolution supported the existence of catalytic effect. This latter was connected to redox reaction between the metallic particles and nitrate ions either in solution or at the PGM/UO2/solution interface. The involved reactions induced the formation of nitrogen species close to the PGM bearing particles. Among them, nitrous acid played an important role due to its strong oxidative power regarding to U(IV). Additionally, no synergistic effect was evidenced when mixing the three PGM elements.