The influence of temperature on the anodic oxidation/dissolution of uranium dioxide

The anodic dissolution of UIVO2 has been studied at 60 °C in 0.1 mol dm−3 KCl using a range of electrochemical methods and X-ray photoelectron spectroscopy (XPS). The results were compared to previous results obtained at 22 °C. This comparison shows that the threshold for the onset of anodic dissolution (−400 mV versus SCE) is not noticeably changed by this increase in temperature. However, both the oxidation of the surface (to UIV/VO2+x) and the rate of anodic dissolution (as UVIO22+) leading to the formation of a UVIO3·yH2O deposit are accelerated at the higher temperature. The XPS analysis shows that the conversion of UV–UVI occurs at lower potentials at 60 °C. Consequently, once the surface becomes blocked by the presence of a UVIO3·yH2O deposit, rapid dissolution coupled to uranyl ion hydrolysis causes the development of locally acidified sites within the fuel surface at lower potentials at the higher temperature.