Dihydrogen H₂ steady state in alpha-radiolysis of water adsorbed on PUO₂ surface

Radiolysis of water adsorbed on PUO₂ surface has been the subject of several studies but still remains poorly understood. The present study brings new experimental results helping to further understand the phenomena occurring at PUO₂ surface. Radiolysis of adsorbed water on PUO₂ surface leads to the reach of a steady state in hydrogen content when relative humidity is kept constant implying an equilibrium between generation and consumption of hydrogen. The influences of specific surface area, relative humidity, PUO₂ dose rate and composition of the atmosphere (Ar vs air) on hydrogen generation were investigated. A significant evolution of the hydrogen generation kinetics was observed upon PUO₂ surface aging. This result might be related to an evolution of the surface physicochemical state induced by a long-term storage in H₂O/H₂/O₂ atmosphere. The surface evolution modifies the equilibrium between generation and consumption of hydrogen. Several annealing thermal treatment were necessary to retrieve H₂ accumulations kinetics similar to the ones obtained with the same sample as freshly prepared. This indicates an important evolution of PUO₂ surface and subsurface. A mechanism is described to explain the surface evolution and its effect on H₂ accumulation through radiolysis of adsorbed water. (authors)