Addition versus radiolytic production effects of hydrogen peroxide on aqueous corrosion of UO2

Abstract The effects of hydrogen peroxide, H 2 O 2 , on UO 2 corrosion is investigated in aerated deionized water in two types of situations. The H 2 O 2 species is either added to water or produced by radiolysis at UO 2 /H 2 O interfaces. The concentrations vary in the range 10 −5 –10 −1  mol l −1 . The radiolysis is induced by irradiating the UO 2 /H 2 O interfaces with a He 2+ -beam emerging from the UO 2 discs into the solutions. Both the evolution of the aqueous solutions and the UO 2 surfaces are characterised. In both types of experiments, the alteration of UO 2 results in the formation of the same secondary phase, an hydrated uranium peroxide called studtite (UO 2 (O) 2  · 4H 2 O). However, the uranium release at the interface differs strikingly. It is much higher when H 2 O 2 is produced by irradiation than when it is simply added. Furthermore, it varies in opposite direction as a function of the H 2 O 2 concentration. This gives evidence that the chemistry at the UO 2 interface under irradiation differs significantly from the chemistry induced by simply adding H 2 O 2 to the solution. Rutherford backscattering spectrometry is used to determine the growth rate of the corrosion layer. For H 2 O 2 addition, the layer thickness increases with increasing leaching time, although as time increases, the U release tends towards zero. It is possible to establish the first empirical equation relating the corrosion rates to the added H 2 O 2 concentrations. For H 2 O 2 radiolytic production, the growth is continuous as irradiation time increases but the growth rate seems to decrease as the layer grows and to reach a limit.