A Comprehensive Electrochemical Impedance Spectroscopic Study of Passive Carbon Steel in Concrete Pore Water

The prediction of corrosion damage to times that are experimentally inaccessible by a large factor (e.g., to over 1000 to 1,000,000 years) is vitally important in assessing various concepts for the disposal of High Level Nuclear Waste (HLNW). Such prediction can only be made using deterministic models, whose outputs are constrained to being "physically real" by the time- and space-invariant natural laws [conservation of mass, energy, charge and mass-charge equivalence (Faraday's Law)]. In this paper, we explore the long-term passivity behavior of carbon steel in contact with concrete pore water solution at 80°C [sat. Ca(OH)2 + sufficient NaOH to yield pH25C = 13.5] by modeling the electrochemical impedance spectroscopic behavior using the Point Defect Model. As a result, we developed a single set of kinetic parameters that might be used, in order to predict the accumulation of general corrosion damage to the supercontainer in Belgium's HLNW clay repository. The results of the optimization indicate that iron interstitials are the dominant defects in the defective barrier oxide layer and that the diffusivity of the defect calculated to be ≈10−15 cm2 s−1.