Helium behaviour in stoichiometric and hyper-stoichiometric UO_2

摘要

Understanding the long-term behaviour of the UO_2 spent fuel in terms of helium build-up and oxidation is a very important issue for safety aspects of storage and disposal. Although helium behaviour in stoichiometric UO_2 has been studied by many authors, it has not been well established and there is a lack of experimental studies in non-stoichiometric UO_2. In this study, an infusion technique was chosen to introduce helium in stoichiometric and hyperstoichiometric single and polycrystalline UO_2 and polycrystalline U_3O_8 samples. Characterization of the samples before and after infusion and after thermal desorption measurements were performed by thermogravimetry, X-ray diffraction, laser flash technique and scanning electron microscopy. It was observed that the increase of stoichiometry in UO_2 affects barely the dissolved helium quantity (under the same infusion conditions as in stoichiometric), while it has a more pronounced influence on the helium diffusion. These two effects are much more pronounced for U_3O_8.