On the Behavior of Uranium Dioxide Toward Aqueous Corrosion: Incidence of Electronic Stopping of Fission Fragments

Abstract

The scenario of spent fuel direct storage in a deep geological repository is currently under consideration in many countries. In this approach the nuclear fuel — mainly uranium dioxide —acts as a first barrier towards fission fragment and actinide release. Although the access of water in such a repository is rather unlikely, evaluating the safety of a disposal requires the knowledge of the mechanisms and kinetics of alteration and dissolution of the nuclear fuel in groundwaters. Despite the fact that the reported litterature on the topic is really extensive, it is still a challenging problem due to the complexity of the system: the used nuclear fuel cannot identify with uranium dioxide itself due to both radiation damage and modification of the matrix composition during reactor operation. Parametric studies in well-defined conditions on simple systems are therefore of prime importance in order to determine the relevant parameters involved in the structural transformations of the uranium-oxygen-water systenL The aim of the present work was to study the incidence of the electronic stopping of fission fragments on the behavior of nuclear fuel towards leaching in deionized water under oxidative conditions. Several features were of special interest: (i) quantification of the damage induced by swift-heavy ion irradiation prior to aqueous corrosion; (ii) stoichiometry and oxygen depth concentration of the alterated surface region; (iii) structural transformation of the crystalline structure induced by incorporation of additional O atoms; (iv) comparison between unirradiated and irradiated samples