Groundwater solution composition effects on copper corrosion in deep geological repositories

International designs for safe disposal of spent nuclear fuel in deep geological repositories (DGRs) typically include placing spent fuel in metallic used fuel containers (UFCs), surrounded by low permeability swelling clay buffers, in stable host rock formations, generally below the water table. Understanding the impact of groundwater chemistry on repository performance is an important aspect of DGR safety assessments, including the geochemical interaction of copper-coated UFCs with that groundwater. Research into copper corrosion in DGR relevant environments often uses sodium chloride solutions as analogues for DGR groundwater or as supporting electrolytes in electrochemical studies. It is, however, unclear whether solutions that mimic the expected ion composition of the groundwater will alter copper corrosion behaviour. Here, electrochemical experiments were used, in combination with surface analyses, to determine the corrosion behaviour of Cu in different solution compositions. Copper was exposed to 0.5 M NaCl, 0.25 M NaCl, and an analogue of groundwater found in a Canadian DGR hosted in crystalline rocks of the Precambrian Canadian Shield (based on the previously developed CR-10 model water). It was determined that the presence of oxygen (i.e., oxic vs. anoxic), the ionic strength, and the solution’s composition all impact the corrosion behaviour. A direct relationship between ionic strength and corrosion rate was determined with corrosion rates in solutions with a 0.5 mol/L ionic strength being twice that of solutions with a 0.25 mol/L ionic strength, particularly in oxic environments. The ion composition had an impact on copper corrosion in all instances with the groundwater analogue resulting in lower corrosion rates than the NaCl solutions.