Dissolution of UO2 by one- and two-electron oxidants

In this work, the efficiency of one- and two-electron oxidants in oxidative dissolution Of UO2 has been investigated. This was accomplished by measuring the U(VI)-concentration in solution after exposing UO2-powder to controlled amounts of oxidants in aqueous solution. The oxidants used in this study are H2O2, IrCl62-, CO3.- and OH..H2O2 acts as a two-electron oxidant while the remaining three oxidants are one-electron oxidants. CO3.- and OH. were generated using gamma-radiolysis. The results clearly show that the dissolution yields for one-electron oxidants (per electron pair) are lower than the yields for two-electron oxidants. Furthermore, the yields for one-electron oxidants increase with increasing amount of oxidant (especially at low amounts of oxidant). The rationale for this is that U(VI) is the main soluble species which is formed directly upon two-electron oxidation. For one-electron oxidants the primary oxidation product is U(V) which can form U(VI) upon reaction with a second oxidant. The probability for a second oxidation is however low at low concentrations of oxidant.