Mössbauer study and structural characterization of UO2-Gd2O3 sintered compounds

Samples of UO2 and up to 10 wt% of Gd2O3 were prepared by solid-state reaction under a reducing atmosphere, in a thermal path comprising ramps and dwell times in the temperature range of 900-1750 °C. The sintered material was analyzed by X-ray diffraction and 155Gd Mössbauer spectroscopy. The results showed that for samples annealed up to 900 °C, the gadolinium sesquioxide remained unreacted. However, when the temperature was increased to 1300 °C, a solid-state reaction took place forming mixed oxides. For the more severe sintering condition, at 1750 °C, gadolinia left urania partially unreacted producing a material consisting of two compositions, UO2 (with no dissolved gadolinium) and (U, Gd)O2. The proposed heating cycle provided pellets free from Gd2O3 phase and may be used by the nuclear fuel industry as a suitable sintering process.