Dislocation substructures and networks induced by compression test in polycrystalline UO2 at 1550 °C

Understanding the plastic behavior of UO 2 fuel pellets is a major challenge for nuclear safety, particularly during off-normal operating conditions of pressurized water reactors. This study provides insights into dislocation interactions and sub-grain boundary formation under load at high temperatures. Characterizations using transmission electron microscopy and electron backscattered diffraction are performed on polycrystalline UO 2 pellets deformed using uniaxial compression tests at 1550 °C with a constant strain rate. For the first time, a detailed characterization of various sub-grain boundaries is conducted in UO 2 , including dislocation networks composed of one to three independent dislocation populations with various types of dislocation junctions. Experiments are interpreted using dislocation dynamics simulations and theoretical models, both relying on the elastic theory. This study helps at improving our understanding of high-temperature plastic deformation mechanisms in nuclear fuel at the nanoscale.