Water corrosion of borosilicate glasses - example of nuclear glasses

Glass is the benchmark solution for conditioning high-level long-lived waste. It is an amorphous material that can incorporate a large number of chemical elements with widely varying stoichiometries into a homogeneous matrix, which is particularly the case for fission product solutions resulting from the processing of spent fuel from nuclear power plants. What's more, glass is a relatively easy material to produce: vitrification processes for solid or liquid waste do not require a large number of stages or material transfers, and glass can be poured directly into a storage container. This is the only solidification process compatible with high levels of radioactivity to have been successfully implemented on an industrial scale, when various solidification processes were envisaged in the 1960s. Finally, glass is a durable material, both with regard to the effects of irradiation and water damage. On this last point in particular, the need to quantify the very long-term evolution of fission product confinement capacities in the glass matrix has led to the development of a good understanding of the weathering mechanisms of these glasses, despite the difficulty inherent in the experimental quantification of very low weathering rates.

After recalling some basic characteristics of glasses, and in particular borosilicate glasses whose composition is suitable for nuclear waste conditioning, this article presents the general phenomenology observed during long-term weathering of borosilicate glasses by natural waters, then details the mechanisms of water weathering of these glasses, highlighting the influence of different parameters (temperature, pH, variations in glass composition and weathering solutions) on these mechanisms. Finally, it explains how competition between the various weathering mechanisms leads to different weathering kinetics, representative of solution renewal rates. Experimental methods for characterizing mechanisms and quantifying glass weathering kinetics are also presented.