Dihydrogen H2 steady state in α-radiolysis of water adsorbed on PuO2 surface

Radiolysis of water adsorbed on PuO 2 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 PuO 2 surface. Radiolysis of adsorbed water on PuO 2 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 , PuO 2 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 PuO 2 surface aging. This result might be related to an evolution of the surface physicochemical state induced by a long-term storage in H 2 O/H 2 /O 2 atmosphere. The surface evolution modifies the equilibrium between generation and consumption of hydrogen. Several annealing thermal treatment were necessary to retrieve H 2 accumulations kinetics similar to the ones obtained with the same sample as freshly prepared. This indicates an important evolution of PuO 2 surface and subsurface. A mechanism is described to explain the surface evolution and its effect on H 2 accumulation through radiolysis of adsorbed water.