On the Role of H₂ as an Inhibitor of UO₂ Matrix Dissolution

The study of spent fuel behaviour under disposal conditions is usually based on conservative approaches assuming oxidising conditions produced by water radiolysis at the fuel/water interface. However, the presence of H₂ from container corrosion can inhibit the dissolution of the UO₂ matrix and enhance its long-term stability. Several studies have confirmed the decrease in dissolution rates when H₂ is present in the system, although the exact mechanisms of interaction have not been fully established. This paper deals with a radiolytic modelling exercise to explore the consequences of the interaction of H₂ with radicals generated by radiolysis in the homogeneous phase. The main conclusion is that in all the modelled cases the presence of H₂ in the system leads to a decrease in matrix dissolution. The extent of the inhibition, and the threshold partial pressure for the inhibition to take place, both depend in a complex way on the chemical composition of the water and the type of radiation present in the system.