Corrosion Current Density of the Carbon Steel API 5L X65, in Contact with Natural Callovo-Oxfordian Clay Pore Water, Assessed by Various Electrochemical Methods during 180 Days

Near-neutral pH and low redox potentials (EH) are considered favorable conditions for radionuclides immobilization in deep repository systems in clay geological formations. Cigeo is a future Industrial Centre for Geological Disposal for Nuclear Waste (NW) for high-level and intermediate level long-lived radioactive waste, to be built in France, at 500 m depth within the Callovo-Oxfordian clay formation. Deep knowledge of the mechanisms and kinetics of corrosion occurring at the external surface of tubings made of API 5L X65 carbon steel (CS-X65) in contact with COx pore water, is essential for a reversible NW management of the Cigeo site. By using robust handmade electrodes and electrochemical and gravimetric techniques, this work aimed to determine the corrosion phenomenology and kinetics of CS-X65 in contact with COx pore water flowing continuously through a Multi-Parameter Probe (MPP) device, placed at 500 m depth, for more than 180 days. It also aimed at demonstrating the reliability and the robustness of the measurement methodology for the corrosion evaluation of the metallic liner of the future nuclear waste disposal site. Two iron oxidants were encountered, oxygen, who was depleted, and proton, who was accompanied by hydrogen sulfide. Corrosion mechanisms and kinetics were well established for two CS-X65, electrochemically perturbed and not. The corrosion thickness loss rates stand between 0.016 and 0.032 mm/y.