Radiation enhanced diffusion of neodymium in single crystal thin film UO2

Abstract

Radiation-enhanced diffusion (RED) of a Nd buried tracer layer in UO2 thin films was measured with Secondary Ion Mass Spectrometry (SIMS). Samples were irradiated with 1.8 MeV Kr+ over a temperature range from 400 to 800 C. RED in UO2 was found to be in the recombination limited regime. Dose rate dependence measurement showed radiation enhanced diffusivity was proportional to the square root of the irradiation flux, further demonstrating that the diffusion mechanism in the temperature range could be characterized by the recombination limited kinetics. Mixing parameter measurements indicated that ballistic mixing was the dominant mechanism of ion mixing. Thermal diffusion was also measured in the temperature range above. A very small yet observable diffusivity was measured at 800 C. A comparison of the diffusion properties between UO2 and CeO2 showed different behavior of the two materials, which indicated that the CeO2 system might not be a good surrogate for the UO2 system in terms of radiation enhanced diffusion.