The local crystal orientations in these domains were close to that of the original grain. Most of the fission gas bubbles were located on the boundaries. Their shapes were far from spherical and far from lenticular. No interlinked bubble network was found. These observations shed light on previous unexplained observations. They plead for a revision of the classical description of fission gas release mechanisms for the center of high burn-up UO2. Yet, complementary detailed observations are needed to better understand the mechanisms involved. | Focused ion beamescanning electron microscope examination of high burn-up UO2 in the center of a pellet
