Article pubs.acs.org/JPCC
Radiolytic Corrosion of Uranium Dioxide: Role of Molecular Species Ali Traboulsi,† Johan Vandenborre,*,† Guillaume Blain,† Bernard Humbert,‡ Jacques Barbet,§ and Massoud Fattahi† †
SUBATECH, UMR 6457, Ecole des Mines de Nantes − CNRS/IN2P3, 4 rue Alfred Kastler, La Chantrerie Bp 20722, 44307 Nantes cedex 3, France ‡ Institut des Matériaux Jean Rouxel, UMR 6502, Université de Nantes − CNRS, 2 rue de la Houssinière, BP 322229, 44340 Nantes, France § Cyclotron Arronax, 1 rue Arronax, CS 10112, 44817 Saint Herblain cedex, France ABSTRACT: In this work, the oxidative corrosion of UO2 particles by molecular species produced by 4He2+ radiolysis of water (simulated by irradiation with a 4He2+ beam) has been investigated as a function of the absorbed dose under open and closed atmospheres. This work was carried out by coupling for the first time (1) characterization of the UO2 surface after oxidation, (2) analysis of H2 and H2O2 produced by water radiolysis, and (3) quantification of the uranium species leached into the solution during irradiation. Oxidation of the surface of the UO2 particles was characterized by Raman spectroscopy. H 2 and H 2 O 2 were analyzed by micro gas chromatography and UV−vis spectrophotometry, respectively. Inductively coupled plasma mass spectrometry was used to quantify the soluble uranium species released into the solution. The results showed that, when the ultrapure water above the UO2 particles was irradiated in an open atmosphere, metastudtite was formed on the UO2 surface, indicating its oxidation by the H2O2 produced by water radiolysis. This oxidation was accompanied by migration of soluble uranium species [U(VI)] into the irradiated solution. After irradiation in a closed atmosphere, oxidation of the UO2 surface and migration of soluble uranium species were limited due to the presence of H2. The inhibition does not occur by direct effect of H2 on H2O2 but more probably by adsorption of H2 molecules on the UO2 surface.
1. INTRODUCTION Management of nuclear waste such as spent nuclear fuel is one of the major political, social, and scientific concerns in countries using nuclear industry.1 Among various management possibilities, the concept of direct disposal of this high-level waste in deep geological vaults (500−1000 m in depth) is being seriously considered by several countries.2 In this case, the spent nuclear fuel will be stored in canisters (made of steel or copper) in the presence of a series of natural and artificial barriers whose aim is to protect the biosphere from eventual radioactive contamination by insulating the waste from the outside environment.3 However, the impact of these disposal repositories on the environment over tens or hundreds of thousands of years is still being studied. In the concept of deep geological disposal, groundwater is assumed to be able to percolate within geological time scales (≥300−1000 years)4,5 through the different barriers and arrive at the nuclear waste package. Considering the scenario of canister failure, groundwater could then come into direct contact with the spent fuel. It is therefore crucial to study the behavior of the spent fuel in the presence of water under real conditions encountered in deep geological sites to predict its possible dissolution mechanism and dissolution rate and, thus, the migration of radioactive elements into the environment. In fact, the spent nuclear fuel matrix is formed mainly by uranium © 2013 American Chemical Society
dioxide (UO2) with a small fraction (
