Synchrotron-Based Micro-CT Investigation of Oxic Corrosion of Copper-Coated Carbon Steel for Potential Use in a Deep Geological Repository for Used Nuclear Fuel
Department of Chemistry, the University of Western Ontario, London, ON N6A 5B7, Canada
Surface Science Western, the University of Western Ontario, London, ON N6G 0J3, Canada
Nuclear Waste Management Organization, Toronto, ON M4T 2S3, Canada
Author to whom correspondence should be addressed.
Geosciences 2018, 8(10), 360; https://doi.org/10.3390/geosciences8100360
Received: 14 August 2018 / Revised: 17 September 2018 / Accepted: 20 September 2018 / Published: 26 September 2018
(This article belongs to the Special Issue The Development and Use of Synchrotron Radiation Techniques for the Geological Disposal of Radioactive Wastes)
Within the multi-barrier system proposed for the permanent disposal of used nuclear fuel, the primary engineered barrier is the sealed metallic container. The present Canadian container design utilizes a carbon steel vessel coated with Cu for corrosion protection. In the event of a defect in the Cu coating that exposes the steel substrate, galvanically accelerated corrosion of steel is, in principle, possible. In this work, the progression of corrosion at a simulated through-coating defect in 3.0 mol/L NaCl solution containing dissolved O2 was monitored using electrochemical measurements and imaged non-destructively using synchrotron X-ray micro computed tomography (micro-CT). The damage volume at the base of the simulated defect was measured from the 3D micro-CT data and used to calculate the amount of O2 used to drive steel corrosion. The results demonstrate that the availability of O2 determines the rate and overall extent of corrosion, while the coatings produced using different deposition and treatment methods (cold spray deposition, heat-treated cold spray deposition, electrodeposition) lead to different corrosion propagation geometries, with the distribution of damage depending on the quality of the Cu/steel interface.