Radiolytic corrosion of uranium dioxide induced by He2+ localized irradiation of water: Role of the produced H2O2 distance

The short-range (few μm in water) of the α-emitting from the spent fuel involves that the radiolytic corrosion of this kind of sample occurs at the solid/solution interface. In order to establish the role of localization of H 2 O 2 species produced by the He 2+ particle beam in water from the surface, we perform UO 2 radiolytic corrosion experiment with different distance between H 2 O 2 production area and UO 2 surface. Then, in this work, the radiolytic corrosion of UO 2 particles by oxidative species produced by 4 He 2+ radiolysis of water was investigated in open to air atmosphere. The dose rate, the localization of H 2 O 2 produced by water radiolysis and the grain boundaries present on the surface of the particles were investigated. UO 2 corrosion was investigated by in situ (during irradiation) characterization of the solid surface, analysis of H 2 O 2 produced by water radiolysis and quantification of the uranium species released into the solution during irradiation. Characterization of the UO 2 particles, surface and volume, was realized by Raman spectroscopy. UV–vis spectrophotometry was used to monitor H 2 O 2 produced by water radiolysis and in parallel the soluble uranium species released into the solution were quantified by inductively coupled plasma mass spectrometry. During the He 2+ irradiation of ultra-pure water in contact with the UO 2 particles, metastudtite phase was formed on the solid surface indicating an oxidation process of the particles by the oxidative species produced by water radiolysis. This oxidation occurred essentially on the grain boundaries and was accompanied by migration of soluble uranium species (U(VI)) into the irradiated solution. Closer to the surface the localization of H 2 O 2 formation, higher the UO 2 oxidation process occurs, whereas the dose rate had no effect on it. Simultaneously, closer to the surface the localization of H 2 O 2 formation lower the H 2 O 2 concentration measured in solution. Moreover, the metastudtite was the only secondary phase formed whatever the irradiation conditions. One hypothesis proposed in this work is the H 2 O 2 may undergo a dismutation reaction leading to the formation of OH at the UO 2 surface.