Oxygen self-diffusion in polycrystalline uranium-plutonium mixed oxide U0.55Pu0.45O2

Atomic transport properties in uranium-plutonium mixed oxides U1-yPuyO2 are of essential concern because they impact numerous aspects of their physicochemical behavior at all stages of the fuel cycle. In this paper, we report oxygen tracer diffusion coefficients in homogeneous U0.55Pu0.45O2 mixed oxide. The study is based on tracer diffusion coefficient measurements obtained using Secondary Ion Mass Spectrometry (SIMS) following diffusion annealing involving gas-solid 18O/16O isotopic exchange. As for other fundamental material properties governed by the nature and behavior of point defects, we show that a careful study of tracer diffusion coefficients as a function of oxygen partial pressure and temperature is liable to provide insight into prevailing diffusion mechanisms. Under the conditions studied in this work, it appears that oxygen diffusion is vacancy mediated.