(Invited) Investigating Galvanic Corrosion at a through-Coating Defect on Cu-Coated Carbon Steel Using X-Ray Micro Computed Tomography (μ-CT)

Abstract

The Nuclear Waste Management Organization (NWMO) is preparing to implement the safe long-term disposal of Canada’s used nuclear fuel in robust, corrosion-resistant used fuel containers (UFC). The current UFC design employs a strong carbon steel vessel, coated with copper for corrosion protection. This project explores corrosion processes that could happen on the surface of a container with a through-coating defect that exposes a small area of the underlying carbon steel, in contact with the copper coating, which corrosion scientists would consider a risk for galvanic (dissimilar metal) corrosion. High resolution ex situ and operando observations of Cu-coated carbon steel specimens with an artificial defect penetrating the copper to the steel, exposed to saline solutions with and without dissolved oxygen, have been made using X-ray micro computed tomography (μ-CT) to reveal the three-dimensional form of the corrosion damage and follow its progression with time (as shown for example in Figure 1). These measurements have shown that the form of the corrosion damage is dependent on both the type of additive manufacturing procedure used to create the Cu coating (electrodeposition or cold spray deposition) and the quality of the Cu/steel interface. In the presence of oxygen, the volume of corrosion damage increases linearly with time, independent of the type of coating, but with a rate dependent on the availability of oxygen. In the absence of oxygen, the corrosion rate is low and decreases with time. Post-experiment characterization of corrosion products by Raman spectroscopy indicated the presence of akageneite (β-FeOOH) and lepidocrocite (γ-FeOOH), depending on the solution conditions within the corroding defect. Figure 1