Hydrogen yields from water on the surface of plutonium dioxide

The long term storage of separated plutonium dioxide (PuO2) in sealed canisters requires an understanding of the processes occurring within the cans. This includes potential mechanisms that lead to can pressurisation, including the radiolysis of adsorbed water forming hydrogen. New measurements of H2 production rates from three sources of PuO2 show low rates at low water monolayer coverage but a sharp increase between 75% and 95% relative humidity. This behaviour being quite different to that reported for CeO2 and UO2, which, therefore, cannot be considered as suitable analogues for PuO2/H2O radiation chemistry. It is concluded that surface recombination reactions are likely to be important in the radiation chemistry and that the H2 production arises from a radiolytic process and not a thermal reaction, at least in these experiments.

► Hydrogen evolution due to water radiolysis on samples of Sellafield PuO2. ► Sharp increase in hydrogen evolution above 75% relative humidity. ► Hydrogen evolution due to radiolytic rather than thermal reaction. ► Analysis of trends from literature data.