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The proposed long‐term management plan for used nuclear fuel is to isolate it within a multiple‐barrier system underground in a deep geological repository (DGR). In the Canadian design, used fuel bundles will be sealed in copper‐coated carbon steel used fuel containers, encased in blocks of bentonite clay, emplaced approximately 500–800 m below ground, and surrounded by a bentonite gapfill material. A laboratory experimental campaign has been undertaken to demonstrate the integrity of the multiple‐barrier system. DGR‐relevant copper materials were embedded in bentonite clay, compacted to various densities, and sealed into a hermetic pressure vessel pressurized with demineralized water. Experiments explored the influence of bentonite compaction in the range of 1100–1600 kg/m3 on copper corrosion over durations of 1–18 months. Postexposure analysis of the copper coupons showed nonhomogeneous corrosion, with corrosion products composed of Cu2O, with some Cu2S. The average corrosion rates decreased as a function of time and increasing bentonite compaction density. In general, we observed that higher bentonite compaction density suppressed the corrosion of embedded copper. [ABSTRACT FROM AUTHOR]

The strategy for the permanent disposal of high‐level nuclear waste in Canada involves sealing it in a copper‐coated steel container and burying it in a deep geologic repository. During the early emplacement period, the container could be exposed to warm humid air, which could result in the condensation of nitric acid, produced by the radiolysis of the humid air, on the copper surface. Previous studies have suggested that both nitrate and oxygen reduction will drive copper corrosion, with the nitrate reduction kinetics being dependent on the concentration of soluble copper(I) produced by the anodic dissolution of copper in the reaction with oxygen. This study focused on determining the kinetics of nitrate and oxygen reduction and elucidating the synergistic relationship between the two processes. This was investigated using corrosion potential and polarization measurements in conjunction with scanning electron microscopy and X‐ray photoelectron spectroscopy. Oxygen reduction was shown to be the dominant cathodic reaction with the oxidation of copper(I) to copper(II) by nitrate, promoting the catalytic cycle involving the reaction of copper(II) with copper to reproduce copper(I). [ABSTRACT FROM AUTHOR]

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. This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems. [ABSTRACT FROM AUTHOR]

The corrosion behavior of copper cold spray coatings on a carbon steel substrate was compared to that of commercially available wrought copper under the conditions anticipated in a nuclear waste repository. Corrosion potential and linear polarization resistance measurements were conducted over 90 d to 120 d in 3.0 mol/L NaCl under anoxic (1) and oxygenated-to-anoxic (2) conditions to simulate the long (1) and short (2) term redox conditions expected in a Canadian repository. Scanning electron microscopy and x-ray diffractometry were used to observe the morphology of the corroded surface and to identify the corrosion products formed. The two specimens behaved very similarly under both sets of conditions. Negligible corrosion was observed under anoxic conditions and the formation of both Cu+1 (Cu2O) and Cu+2 (Cu2(OH)3Cl) phases occurred under oxygenated conditions. No evidence was observed to suggest the particle boundaries in the cold sprayed coating were preferential corrosion sites. [ABSTRACT FROM AUTHOR]

The corrosion of high level nuclear waste containers under permanent disposal conditions can occur via a number of processes which change in importance as the environment within a deep geologic repository evolves from oxic to anoxic. The container design involves a copper coating on a steel vessel. The characteristics of these coatings are being assessed using standard analytical methods, including microscopy and electron backscatter diffraction. The corrosion processes on the surface of the coatings and at through-coating defects are also being investigated electrochemically. Although minor differences exist, the surface corrosion of cold sprayed and electrodeposited coatings generally exhibited similar corrosion behaviour to standard wrought copper. Corrosion at the base of a simulated through-coating defect in a cold-sprayed coating was found to proceed via galvanic coupling to oxygen reduction on the coating surface. Besides accumulating damage at the base of the defect, corrosion propagated along the copper/steel interface, most likely a consequence of the damage inflicted during the deposition process. [ABSTRACT FROM AUTHOR]