UO 2 oxidation site densities determined by one- and two-electron oxidants

Abstract

The oxidation site density (number of oxidation sites per m 2) for UO 2 powder was determined by measuring the amount of oxidant needed to fully oxidize the surface (denoted the critical oxidant conversion). The point where the surface becomes fully oxidized is identified by a change in reaction order from first to zeroth order in HC O 3 - free systems. At the critical oxidant conversion the kinetics of the reaction becomes completely governed by dissolution of oxidized UO 2. The oxidants used in this study are H 2O 2 (two-electron oxidant) and IrC l 6 2 - (one-electron oxidant). The oxidation site densities determined using the two different oxidants are (2.1 ± 0.1) × 10 −4 and (2.7 ± 0.5) × 10 −4 mol m −2, respectively, expressed in two electron equivalents. The fairly good agreement between the two oxidants implies that the methodology used indeed gives a reasonable measure of the oxidation site density. In addition, oxidation site densities for different size fractions of UO 2 powder were determined. The results are discussed in terms of surface roughness.