Chemical reactivity of argillaceous material in engineered barrier: Rare earth disilicate formation under subcritical conditions

The Deep Geological Repository (DGR) is the most internationally accepted option for the storage of high radioactive wastes. This confinement is based on the multibarrier concept where the engineered barrier is crucial for the safety of the repository. Nowadays, bentonite is accepted as the best argillaceous material in the engineered barrier of DGR. Additionally to its well-known physical role, a chemical interaction between lutetium, as actinide simulator, and the smectite has been demonstrated. The aim of this paper is the study of the hydrothermal reaction of smectite and a wide set of rare earth cations as trivalent actinide simulators. Saponite was submitted to hydrothermal treatment at 300 °C with a solution of REE3+ cations (REE = Sc, Lu, Y, Sm, Nd and La). The products were analyzed by XRD, NMR and electron microscopy. Under hydrothermal conditions, saponite formed rare earth silicates. The final products and the reactivity of saponite depend on, among other factors, the nature of those cations.