Sintering of Silica Aerogels for Glass Synthesis: Application to Nuclear Waste Containment

To ensure long-term storage, long-life nuclear wastes (actinides) must be incorporated in a matrix exhibiting excellent chemical durability. Among the usual glasses, silica glass, which does not contain alkali and boron, is expected to present high durability. Associated with good mechanical properties, a low thermal expansion, and consequently a good thermal shock resistance, silica glass is a promising candidate. However, the glass preparation requires a high temperature (1,800°C) melting process. Nevertheless, silica glasses can be synthesized from silica aerogels followed by a sintering in a temperature range (1,000°C) close to half of that of the glass melting process. The impregnation of aerogels by actinide solutions followed by aerogels sintering has been proposed. After sintering, the aerogel silica matrix traps the nuclear waste and protects them against water erosion. The resulting material is a nanocomposite material (glass-ceramic) composed of nuclear wastes embedded in the silica matrix. The dissolution rate of such a composite in water is almost 102 times lower than that of the common nuclear glasses. This result clearly proves the improvement of the chemical durability of the glass-ceramic made from aerogels and, thanks to the high mechanical properties, these new materials can be suitable matrices for the containment of actinides. This contribution describes the different steps of the gel–aerogel–glass transformations and the characterization of the durability and mechanical properties of such glass- ceramics trapping the nuclear waste. The interest of silica aerogel as host matrix for nuclear waste containment is emphasized.