Annealing behavior of (Pu,Cm)O lattice and bulk expanded by self-irradiation damage

Takano, Masahide ; Akabori, Mitsuo; Arai, Yasuo

To investigate the influence of self-irradiation damage and accumulation of He in oxide fuel pellets containing minor actinides, the expansion and annealing behavior of the crystal lattice and bulk were examined comparatively on a (PuCm)O specimen. The lattice parameter and pellet dimension at room temperature grew with the similar dependence on storage time, and their linear expansion saturated to 0.3 % within 60 days. After two years storage, the annealing examinations were performed in the temperature range up to 1433 K. The lattice parameter recovered to the undamaged value, whereas the pellet dimension grew again during the heat treatment at 1433 K. The fractured surface of the annealed pellet was then observed by a scanning electron microscope. The gas bubbles with 200-300 nm in diameter were recognized along the grain boundaries like the fission gas bubbles. It was considered the dissolved He atoms moved toward grain boundaries by diffusion and formed gas bubbles, which resulted in the He gas swelling of the pellet specimen.