Annealing behavior of (Pu,Cm)O2 lattice and bulk expansion from self-irradiation damage

In order to investigate the effect of self-irradiation damage and accumulation of He on oxide fuel pellets containing minor actinides, the expansion and annealing behavior of (Pu0.95Cm0.05)O2 lattice and bulk were examined comparatively. Since the lattice and bulk expansion at room temperature showed a similar dependence on the storage duration, the main factor of bulk expansion was found to be the lattice expansion due to the generation of point defects. The lattice parameter recovered to the undamaged value by annealing at 1429 K for 2 h, whereas the bulk expanded again by annealing at 1433 K and did not recover to the undamaged value. In the micrographs of the fracture surface of the annealed pellet, the formation of gas bubbles along grain boundaries was confirmed. The He gas bubble formation resulted in the pellet swelling, and it may affect the pellet thermal conduction.