Abstract
The polished hemispheres of ThO2 kernels were irradiated by fission fragments, which recoiled from the covered Al-U alloy foils. After irradiation, the lattice parameters of the kernels were measured by microbeam X-ray diffractometer. It was found that the lattice parameter increased initially in a linear relationship with increasing fission fragment dose and reached a saturation value at doses higher than about 1×1016 fission fragments⋅cm-3. The saturation value was smaller for the fine-grained specimen than for the coarsegrained. The recovery began at about 400°C for both the specimens and lasted to higher temperature for the coarse-grained.
