Photos (a) and (b) show the appearance of simulated debris samples with ZrO₂ contents of 10 and 65mol%, respectively. Photos (c) and (d) show the respective cross-sectional images of these samples. ZrO₂ content represents the cladding tube component. There are no defects, such as cracks in the external surface. The portion that is visible in the spotty pattern shows the grain boundary in the cross section. These grain sizes are 10－40 μm.