Reaction sintered glass: a durable matrix for spinel-forming nuclear wastecompositions

Glass formation by reaction sintering under isostatic pressure is an innova tive process to vitrify refractory-rich high-level radioactive waste. We us ed a typical defense waste composition, containing spinel-forming component s such as similar to 4 wt% of Cr2O3, similar to 23 wt% Al2O3, similar to 13 wt% Fe2O3, and similar to 9 wt% UO2, with CeO2 simulating UO2. Reaction si ntered silicate glasses with waste loading up to 45 wt% were prepared withi n three hours, by hot pressing at 800 degrees C. The glass former was amorp hous silica. Simulated waste was added as calcined oxides. The reaction sin tered glass samples were characterized using scanning and analytical electr on microscopy. The results show that extensive reaction sintering took plac e and a continuous glass phase formed. Waste components such as Na2O, CaO, MnO2, and Fe2O3, dissolved completely in the continuous glass phase. Cr2O3, Al2O3, and CeO2 were only partially dissolved due to incomplete dissolutio n (Al2O3) or super-saturation and reprecipitation (Cr2O3 and CeO2). The pre cipitation mechanism is related to a time dependent alkali content in the d eveloping glass phase. Short-term corrosion tests in water showed that the glasses are chemically more durable than melted nuclear waste glasses. Base d on hydration energies calculations, the long-term chemical durability of our reaction sintered glasses is expected to be comparable to that of rhyol itic and tektite glasses. (C) 2000 Elsevier Science B.V. All rights reserve d.