Influence of annealing and high energy ion irradiations on the Xe state in UO2

Uranium dioxide is used as standard nuclear fuel in light water reactors. During in-reactor operations, UO2 is subjected to simultaneous irradiations of various energetic particles. Fission fragments, like rare gases (Kr, Xe), transfer their energy to atomic nuclei and/or electrons of the UO2 matrix and induce a significant amount of damages, in particular gaseous bubbles, affecting the fuel in pile performances. To better understand the fuel changes, we are studying the Xe bubble growth and re-solution in UO2. Xe implantations at high-fluence were first carried out, followed by various thermal annealing to obtain different bubble populations, and finally different high-energy ion irradiations to promote re-solution. TEM was used to follow the Xe bubble evolution at nanometric scale. XAS measurements would allow us to obtain more information on the Xe state and environment with a larger representative volume after annealing and re-solution.