[en] 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_2O_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_2O_2 production area and UO_2 surface. Then, in this work, the radiolytic corrosion of UO_2 particles by oxidative species produced by "4He"2"+ radiolysis of water was investigated in open to air atmosphere. The dose rate, the localization of H_2O_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_2O_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_2O_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_2O_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_2O_2 formation lower the H_2O_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_2O_2 may undergo a dismutation reaction leading to the formation of OH at the UO_2 surface.