Modifications of oxidized Zircaloy-4 surface in contact with radiolysed wet air

International audienceIn the framework of radioactive waste geological disposal, the long term evolution of the nuclear wastes packages and the release of the radionuclides from the wastes have to be studied. Regarding compacted wastes (cladding tubes) coming from reprocessing of spent fuel, the Zircaloy-4 (zirconium alloy) cladding tubes have been activated and oxidized in reactors. In the disposal, the radioactive waste is exposed to humid air in a first phase and to water after the resaturation phase. In order to better assess the degradation process of these nuclear waste package, the influence of wet air proton radiolysis on the behavior of surface oxidized Zircaloy-4 has been investigated. Radiolysis experiments were performed using an irradiation cell which is associated to an extracted beam. Samples are exposed to wet air, under and without radiolysis, during 12 and 24 h. The water partial pressure has been fixed at 6 and 50 mbar in order to have, respectively, localized adsorbed water molecules and a thin film of adsorbed water. Before and after each treatment, sample surfaces were characterized by X-ray Photoelectron Spectroscopy (XPS) in order to identify the elements at the topmost surface of the solid. The wet air radiolysis causes changes at the surface of oxidized Zircaloy-4 and influences the corrosion phenomenon. Indeed, an enrichment of tin and the presence of nitrogen species were observed. It could be due to the formation of tritin(II) tetrahydroxide dinitrate and a Zr4+ tetramer on the topmost oxide surface

PROCESSUS PRIMAIRES EN CHIMIE SOUS RAYONNEMENT. INFLUENCE DU TRANSFERT D'ENERGIE LINEIQUE SUR LA RADIOLYSE DE L'EAU

ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Researches in safety of compacted waste and spent nuclear fuel

International audienceIRSN (the French Institute of Radioprotection and Nuclear Safety) is in charge of reviewing the LL-HLW geological repository project managed by ANDRA (the French National Radioactive Waste Management Agency) in support of the nuclear safety authority (ASN). Amongst other IRSN paies particular attention to the performance of confinement of the nuclear wastes packages, to the release of the radionuclides from the wastes and the associated uncertainties. In order to better assess the degradation process of the nuclear waste packages, IRSN has developed an experimental program in collaboration with laboratories from the university, the ENSMSE (École nationale supérieure des mines de Saint-Étienne) and the CNRS (the French National Center for Scientific Research). The studies concern on the one hand the activated compacted wastes packages and on the other hand the spent fuel.Regarding compacted wastes packages, at the end of the light water reactors operation, the Zircaloy (zirconium alloy) cladding tubes had been activated and oxidised. After processing, these cladding tubes are compacted in a wafer form, placed into a steel container, and then into a concrete over-pack with a view to being disposed of in geological repository. These wastes are mostly composed of activated oxidized metal pieces which also contain traces of fission, activation products and actinides. In the repository, they are exposed to radioactivity in presence of resaturation water. The water radiolysis may accelerate the oxidised metal corrosion processes. By the way, the wastes degradation is mainly due to corrosion process. A fundamental study has thus been defined on the effects of water radiolysis on Zircaloy corrosion. The second study aims at better understanding the influence of the fuel matrix defects on the radiolytic degradation of spent fuel. As a matter of fact, fission products and actinides decay during storage may cause defects of the fuel matrix by changing its composition and microstructure. The study is performed in close collaboration with CNRS laboratory