X-ray photoelectron spectroscopy (XPS) study of surface oxidation of UO2 doped with Gd2O3 at different temperatures and atmospheres

Abstract

In this work, the influence of GdIII doping on the surface oxidation of UO2 has been investigated in situ by XPS. The samples were put in contact with either hydrogen, argon or synthetic air streams saturated with water and were heated at different temperatures (60, 200 and 350 °C). The results indicated that, in absence of porosity, doping UO2 with Gd2O3 completely inhibited the oxidation of UO2. Such behaviour could be explained by the matrix stabilization effect of gadolinia (Gd2O3). However, for porous samples, the oxidation of UO2 in presence of Gd2O3 depends strongly on the surrounding gas atmosphere. In presence of hydrogen, the oxidation was significantly supressed, particularly above 200 °C, due to the hydrogen reducing effect. At 350 °C and in the presence of argon, the reactivity of the samples increased slightly when comparing to H2, whereas in contact with synthetic air, the complete oxidation of the samples could not be prevented by Gd2O3. These results could be explained by assuming that the porosity might favour the oxidation of the samples. Therefore, the presence of porosity in the samples is an important parameter to consider when studying the surface oxidation of UO2 doped with Gd2O3.