FEMU based identification of the creep behavior of Zircaloy-4 claddings under simulated RIA thermo-mechanical conditions

Abstract : This study aims to identify the creep behavior of Zircaloy-4 fuel claddings under simulated reactivity initiated accident (RIA) thermo-mechanical conditions. In a previous work ballooning creep tests performed in simulated RIA conditions were described. A challenge to overcome when analyzing these experiments is that ballooning tests imply structural effects during the deformation of the specimen that have to be taken into account to identify the creep behavior of the material. In this paper a FEMU (finite element model updating) based identification is proposed to identify the creep law of the cladding, weakly coupled to the phase transformation of the material at high temperatures. Since the loading conditions are solely known in the part of the optical field of the cameras used for stereocorrelation, only this region is modeled using a Love-Kirchhoff assumption to impose the boundary conditions through the sample thickness. A Norton creep law, whose parameters are expressed as a function of the β phase fraction in the material, is identified and reproduces the first 10 seconds of the experiments with mean errors on the radial displacement rates of about 10%. Finally, an extension to higher time scale is proposed in Norton's law to model the non linearity in the material response by taking into account the grain growth contribution.