There is international consensus that the environmentally safest place to dispose of toxic radioactive waste is deep underground. Because transport of contaminants occurs in solution, i.e. via the pore water, repositories of radioactive waste will be built within geological formations where water movement is expected to be slow. The chemical characteristics of pore waters in low-permeability rocks contain valuable archives of geochemical conditions that prevailed in the distant past and of processes that occurred since then, often over millions of years. We can learn from Nature by understanding such processes and use this information to predict the expected future evolution of the repository environment. A multi-barrier concept is envisaged, in which metal canisters holding the waste are embedded in swelling clays (which seal against moving groundwater) and cement, and the entire repository is excavated within a low permeability host rock.
Research is needed to understand in detail how these repository components act as barriers and how radioactive contaminants could migrate outwards once the protecting canister has corroded. Based on laboratory and underground experiments, the future behaviour of the repository in its geological setting is predicted by numerical modelling. This is an unusual case for geologists and geochemists, because here the challenge is to predict the future.
Our group has been involved in numerous research projects targeted at radioactive waste over the past 30 years. We focus on the geochemistry of host rocks acting as aquitards and on the geochemistry and hydrogeology of the surrounding aquifers. A further research field includes the geochemistry of bentonite (a swelling clay material) and cementitious materials used in underground structures. We take an integrated approach that combines field work (e.g. drilling campaigns) with laboratory studies and state-of-the-art reactive-transport modelling.
