1Effect of External Hydride Layer on Fuel-Cladding Deformation during EDC- Testing

The Expansion Due to Compression (EDC) test has been developed for the study of irradiated and hydrided cladding failure, under conditions of pellet cladding mechanical interaction, which are expected during a reactivity initiated accident (RIA) or an in-pile test. During the experiment, a pair of pistons compresses a polymer pellet, which is placed inside a fuel cladding tube. The diameter of the pellet increases, leading to development of contact pressure on the internal surface of the tube. The part of the tube, which is in contact with the pellet, suffers relatively high tensile hoop stress. Finite element simulations of the EDC-test are performed with the objectives: (i) to understand the deformation of the cladding, during the experiment and (ii) to provide information, necessary for the development of failure criteria. The effect of external oxide and hydride layers on cladding deformation, during the EDC-test, is discussed. The zirconium alloy in the cladding is assumed to be elastic-plastic with or without hardening. On the other hand the external hydride and oxide layers are assumed to behave only elastically. Calculations have been performed for different hydride layer thickness. The oxide layer, when considered in the present calculations, has the thickness of the innermost adherent layer, measured in used fuel cladding tubes. The distributions of important field quantities, with respect to the damage of the cladding, as well as th