Retention of Aqueous 226Ra Fluxes from a Subaqueous Mill Tailings Disposal at the Bois Noirs Site (Loire, France)

This study focuses on a subaqueous mill tailings disposal site located in France (Bois Noirs) where 1.3 million tons of uranium mill sludge (fine tailings fraction < 50 μm) have been disposed since the 60ʹs in a man-made pond below 4 meters of water maintained artificially by a rock-fill dam. A significant attenuation of aqueous 226Ra activity is observed in ground waters. This paper presents the preliminary modeling work performed for evaluating the role of water-rock interactions on aqueous 226Ra attenuation through the dam. This modeling attempt, assuming thermodynamic equilibrium, aims at checking the hydrochemical conceptual model developed in a previous study, in which Ra retention through the dam was assumed to most likely result from sorption onto metallic oxide-hydroxides. A 2D coupled reactive transport model was conceived to test this hypothesis over time and identify the measurements required to verify its consistency over the long term.