Selenate reduction in environmental geomedia

Due to its long half-life and high activity, 79Se is an important radionuclide to monitor for a correct assessment of the safety of nuclear waste repositories. Selenate [Se(VI)], the most oxidized form of Se, is an anion with high mobility in the pore waters of the clayey formations that will host the French repository for high-activity and long-life nuclear waste. It is known that magnetite, a Fe(II)-bearing phase present as a result of the corrosion of the steel canisters, can reduce selenate to elemental Se, a non-mobile solid species. Here, we aim at studying how carbonate –an ion present in the pore waters of the repository- and Fe(II) –an ion present due to the corrosion of the steel canisters- can affect the reduction kinetics of selenate by interactions at the magnetite-water interface. The presence of these ions could pose kinetic barriers for the reduction. Assessing this risk is essential for reliable assessments of the safety of an underground repository.