Galvanic corrosion of copper-coated carbon steel for used nuclear fuel containers

Abstract

Canada is currently considering Cu-coated carbon steel containers for the long-term storage of used nuclear fuel in a deep geological repository. The Cu coating provides a corrosion-resistant barrier, protecting the underlying steel from coming into contact with groundwater. However, galvanically accelerated corrosion of steel is possible if there is a defect through the Cu coating. To investigate this scenario, the progression of steel corrosion at the base of a simulated though-coating defect was imaged using synchrotron X-ray micro-computed tomography. Results show that coatings produced using different methods (cold spray, annealed cold spray, electrodeposition) lead to different corrosion propagation geometries. These findings can be used for modelling steel corrosion at a though-coating defect under deep geological repository conditions.

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

“…The extent of propagation along the interface is greatest for steel coated with cold spray Cu, less for heat-treated Cu/steel, and least for electrodeposited Cu/steel in all studied conditions. The greater extent of corrosion along the cold spray Cu/steel interface is likely due to its greater roughness and strain, and lower adhesion compared to the electrodeposited Cu/steel, as described previously in more detail [2].…”

“…The micro-CT image slices of cold spray, heat-treated cold spray, and electrodeposited Cu/steel samples exposed for 42 h to an O 2 -sparged 3.0 mol/L NaCl solution, Figures 5-7, and to an air-sparged 3.0 mol/L NaCl solution, Figures 8-10, show how the corrosion front propagated into the steel and along the Cu/steel interface and where corrosion products have been deposited. Selected micro-CT image slices for the samples exposed to O 2 -sparged solution have been shown previously in a summary article [2]. However, for this systematic study, the image slices included here ( Figures 5-7) were chosen so that the 0 h and 42 h images showed the same locations within each sample, and all of the micro-CT images have been colour treated to facilitate differentiation among Cu, steel, corrosion products, and voids.…”

“…Within this proposed multi-barrier system, the key engineered barrier is the robust used fuel container, which consists of a carbon steel inner vessel coated with~3 mm of Cu, applied via cold spray deposition and electrodeposition. The DGR concept and container have been described in detail previously [1][2][3][4][5][6]. Upon closure, the conditions in a DGR will evolve over time, beginning as warm, dry and oxic, and then evolving to cool, wet and anoxic.…”

Exposure tests of copper foils in a slurries of different bentonites

“…Copper is material believed as corrosion resistant in wet bentonite environment of radioactive waste deep geological repositories. It is candidate material for outer case in Scandinavian concept [1][2][3][4][5] and for coating in Canadian [6][7][8][9][10]. Copper is also one of the candidate materials for construction of canisters in Czech concept [11][12][13][14][15][16][17][18].…”

1D simulation of canister galvanic corrosion in saturated compacted bentonite

“…The use of slurry caused a slight increase in the corrosion rate compared to ground waters. The work of Standish et al was rather qualitative, without quantification of the galvanic corrosion rate of carbon steel in a couple with copper. Experiments were carried out in a 3 mol dm −3 solution of NaCl under aerobic and anaerobic conditions.…”