Hydrothermal leaching of rhyolite glass in the environment has implications for nuclear waste disposal

Glass has been widely advocated as a suitable medium for the immobilization of high-level nuclear waste1–6. Methods of vitrification to borosilicate glass are advanced, with processes set up on a semi-industrial scale7–9, but an alternative strategy would be to incorporate waste into a high-silica glass10. It is generally proposed5,6 that vitrified radioactive waste be enclosed in metal canisters and stored underground. However, the presence of heated groundwater in rocks means that the canisters may corrode, allowing hot aqueous fluids to come into contact with the radioactive waste glass and leach out radioactive elements. Numerous laboratory tests have been performed for short periods and at relatively low temperatures to assess the leaching performances of different types of glass11–15, however, extrapolation to predict the long-term behaviour of glasses after burial is very uncertain. I report here a microprobe analysis technique which investigated hydrothermal leaching of rhyolite glass adjacent to a fluid conduit in the Tertiary hydrothermal system of the Isle of Skye, north-west Scotland. As the composition of rhyolite and proposed high-silica radioactive waste glasses are similar, this study may help to predict the long-term leaching behaviour of such glasses after underground burial.