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.

In Situ Study of Particle Precipitation in Metal-Doped CeO2 during Thermal Treatment and Ion Irradiation for Emulation of Irradiating Fuels

“…A sequence of high-angle annular dark-field (HAADF) STEM images for the film under 20 min isochronal annealing at temperatures from 873 to 1373 K are shown in Figure . Our previous study showed formation of small Pd particles (∼3 nm in size) in the as-irradiated film. Those particles are not visible in the low magnification image of Figure a.…”

“…In fact, the calculated atomic ratio of Ru to Mo is 0.80 for 43 GW d/t U after 100 years cooling time as compared to 0.75 in this study. Pd has been found to be the most mobile element among the five dopants in CeO 2 . Pd atoms can be clustered and precipitated to small particles at an elevated temperature, which then become immobile at higher temperatures.…”

Thermal Energy Transport in Oxide Nuclear Fuel

“…In a recent study involving emulated spent fuel, Jiang et al [464] used TEM and APT to study thin films of CeO2 doped with metallic fission products. They found a uniform distribution of doped metals within the as-grown film.…”

Nanoscale oxygen defect gradients in UO 2+ x surfaces

“…A simple estimate using Shannon ionic radii 43 shows that a transition from eightfold-coordinated U 4+ (1 Å) → U 6+ (0.86 Å) amounts to a 14% ion size reduction, in line with the change from Ce 3+ (1.14 Å) → Ce 4+ (0.97 Å) of 17.5%. While CeO 2 possesses a fluorite structure very similar to UO 2 and is often used as a proxy to simulate radiation damage effects, 44,45 we expect even greater channeling behavior due to the higher atomic scattering factor of U (Z = 92) versus Ce (Z = 58). 46 As shown in supplementary Fig.…”