Vitrified nuclear waste durability in complex natural environments

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Understanding the long-term durability of nuclear waste glass in the subsurface is important in the UK and internationally as many countries intend to dispose of vitrified radioactive waste in underground geological disposal facilities. In order to ensure safe disposal, we need to be confident that radioactive elements will remain isolated and immobilised for sufficient time to allow radioactivity to decay to safe levels. There will be multiple barriers in place (e.g. a metal container and engineered backfill) to delay groundwater from reaching the nuclear waste glass but eventually contact with water is expected. Although there are a number of laboratory tests currently used to determine the rate of glass dissolution in water all accelerate corrosion by increasing the temperature, surface area, or both and give very different predictions depending on the test conditions. Laboratory tests are also performed under simplified, stable, sterile conditions and using deionised water taking no account of how changing geochemical conditions will affect glass corrosion rates. This fellowship will combine materials science, geochemistry and geomicrobiology to study how glass corrodes in real-time in dynamic complex natural environments. I will improve understanding of key factors affecting corrosion (temperature, groundwater geochemistry, saturation, and microbiology) using the Ballidon long duration experiment, where glass samples have been buried for nearly 50 years. To predict the durability of nuclear waste glass thousands of years into the future I will study simulant nuclear waste glass's in conditions relevant to UK and US disposal concepts. The result of this novel investigation will be to critically evaluate, and improve, upon durability tests for glass, to build an improved model of glass corrosion and to establish further long duration experiments to inform the safety case for geological disposal in the UK and abroad.