Uranium dioxide oxidation/dissolution mechanism

In the case of deep geological storage of spent fuels, the environment waters will arrive at the surface of the fuel after some thousand years. It is then necessary to understand the leaching mechanisms of the UO2 matrix in contact with the interstitial waters of the potential storage site. At first, the characterization of the intrinsic properties of the UO22+/UO2 system is carried out by an electrochemical way on a uranium dioxide electrode (semi conductor material). The electrochemical parameters of this system such as anodic charge transfer coefficient and standard velocity constant of the electrochemical reaction are determined in the speciation conditions adapted to the study of the UO22+/UO2 redox couple study. The second part deals with the dependence of pH and carbonate ions on the dissolution of UO2. On the other hand, the solid is characterized by ex-situ methods as XPS to reveal the eventual secondary phases precipitated at the surface of the UO2. The aim of this work is to verify that the limiting step to the dissolution of the nuclear ceramics in presence of complexing agents is the progression of the oxidation front. (O.M.)