Analytical study of the aqueous corrosion of uranium dioxide by physico-chemical methods

Sintered uranium dioxide pellets have undergone static leaching tests carried out between 25 and 90°C between 1 day and 12 months. The main aim of this study was to characterize the possible alterations of the UO₂ surface after an aqueous corrosion treatment, by the mean of the Rutherford backscattering spectroscopy, of the scanning electron microscopy and of the photoelectron spectrometry and to measure the release of uranium in solution. The results differ a lot according to the kind of the used leachate (deionized water or Volvic mineral water). The measurements of the uranium concentration in the leachates carried out by laser spectro-fluorimetry show that the release rate of this element increases with temperature in the deionized water and decreases in Volvic water. This last phenomenon is probably due to the formation of an alteration layer rich in magnesium silicate revealed at the surface of the leached samples in 90°C. At this temperature, the first steps of the aqueous corrosion are characterized by a constant U(IV)/U(VI) ratio. The leaching in deionized water brings no perceptible alteration at the surface state and proves that there is in this case a congruent dissolution. (O.M.)