Thermal behavior of fission gases in UO₂ considering radiation-induced defects

During in-reactor irradiation, fission gases such as xenon or krypton are produced. In the fuel, those gases diffuse and precipitate to form bubbles. In addition, fission reactions induce small defects (vacancies and interstitials) and larger defects (cavities and dislocations) formation. Data acquire fission gases migration considering radiation-induced defects is thus necessary to better understand and improve models of in-pile fuel behavior. The experimental approach developed in this work aims to study thermal diffusion of rare gases and to understand their interaction with radiation-induced defects.To do this, separated effect studies were performed coupling ion implantations/irradiations to fine characterization techniques. Positron Annihilation Spectroscopy (PAS) coupled to Transmission Electron Microscopy (TEM) observations allows for defects characterizations (vacancies and/or cavities induced by ion implantation) and for their thermal behavior study. On the other hand, gas release measurements are performed by thermal desorption spectrometry. Simulation of gas kinetic release allows to determine diffusion coefficients and to lighten trapping mechanisms. The synthesis of those various experimental results brings us to identify gas migration mechanism and to describe their interaction with radiation-induced defects. (author)