Nanoparticle Precipitation in Irradiated and Annealed Ceria Doped with Metals for Emulation of Spent Fuels

Abstract

Epsilon-phase alloy precipitates have been observed with varied compositions and sizes in spent nuclear fuels, such as UO2. The presence of the inclusions, along with other oxide precipitates, gas bubbles, and irradiation-induced structural defects, can significantly degrade the physical properties of the fuel. To predict fuel performance, a fundamental study of the precipitation processes is needed. This study uses ceria (CeO2) as a surrogate for UO2. Polycrystalline CeO2 films doped with Mo, Ru, Rh, Pd, and Re (surrogate for Tc) were grown at 823 K using pulsed laser deposition, irradiated at 673 K with He+ ions, and subsequently annealed at higher temperatures. A number of methods, including transmission electron microscopy and atom probe tomography, were applied to characterize the samples. The results indicate that there is a uniform distribution of the doped metals in the as-grown CeO2 film. Pd particles of ∼3 nm in size appear near the dislocation edges after He+ ion irradiation to ∼13 dpa. Thermal annealing at 1073 K in air leads to formation of precipitates of Mo and Pd near the grain boundaries. Further annealing at 1373 K produces 70 nm sized precipitates consisting of nanograins at cavities.