Assessment of an electro-kinetic decontamination process for cementitious materials

In nuclear facilities more than 80% of the volume of contaminated materials is part of the concrete structures, mainly treated by mechanical abrasion and blasting techniques. However, contaminants such as cesium and strontium are transported through the porous material (> 6 cm) and cannot be treated by mechanical techniques. An electro-kinetic remediation process is still under assessment and development as a specific method for deeply contaminated structures. It consists in using the reinforcing steel as an anode and placing a cathode at the surface of the structure, immersed in a conductive electrolyte. The cathode-electrolyte ensures the conduction of electric currents within the material, and imposes an electric field between the two electrodes. The contaminant ions within the pore solution migrate toward the electrolyte. Experiments are performed on mortar cylinders artificially contaminated by nonradioactive cesium to estimate the efficiency of the process at small scale (about 10 cm) on reinforced mortar cylinders. Electrolyte samples are analyzed by ion chromatography to measure the cesium fluxes and decontamination rate. Characterization experiments have been performed to determine the main diffusion and porosity parameters. A model has been developed to describe ion transport under an electrical field. Natural diffusion and ion migration are taken into account, osmosis and convection are neglected. The governing equations are obtained by combining the fluxes expressions with the mass balance equations. Electric and transport phenomena are coupled using the electro-neutrality equation. The numerical outcomes give the evolution of the cesium concentration within the porous media. Electric field and potential iso-lines are calculated for different times. Remaining quantities of ionic species are obtained by integration of mass fluxes. (authors)