Structural damage in a self-irradiated zirconolite-based Ceramic

Abstract

The zirconolite phase of SYNROC nuclear waste was fabricated with 5 mol% 238PuO 2 substituted for a like amount of ZrO 2, in order to induce self-irradiation damage. The resulting product exhibited a matrix of monoclinic zirconolite containing ∼~ 3.8 mol% PuO 2 along with roughly 20 vol.% of the cubic polymorph with approximately twice the PuO 2 content of the matrix. After a dose of 2.1 × 10 25 α decays/m 3 at room temperature (800 d storage) swelling reached 5.5 vol.% and neared saturation. The monoclinic phase became X-ray metamict at ∼~1.0 × 10 25 α/m 3 after slight atomic rearrangement within the crystalline material. Periodic TEM examination revealed a gradual evolution from the crystalline state to an amorphous condition with residual crystallites, consistent with a model involving conversion by alpha recoil tracks. Optical metallography showed extensive microcracking, attributed to differences in swelling rates of the two zirconolite polymorphs.