Figure 6
(a) A scheme imposed on an optical microscopy image of an indent on the pure UO2 pellet with marked a and c, two dimensional parameters used for fracture toughness estimation; (b)SEM images show the indentation induced cracks propagating along grain boundaries in the pure UO2 pellet, resulting in grain spallation and clearly visible grain boundaries; Red box shows where the indent sits; (c) On contrary, the cracks in the UO2-GNP composite fuel pellets can be effectively harnessed by GNP, leaving grain structure behind GPN intact; (d–f) SEM images further show crack tips effectively pined and deflected by GNP.
