Electrochemical behaviour of copper–nickel alloys as immobilisation matrices for the storage of fission products in CO2-enriched synthetic groundwater

•A material selection to immobilise reducible fission products.•Cu–Ni alloys were evaluated in contact with electrolytes simulating groundwater.•Under aerated conditions, Cu into the Ni alloy affects passive film resistance.•In CO2-saturated media, Ni is in pre-passive field which affect the passive film.•The addition of copper will be limited to 30 wt% Cu.

The surface properties of nickel and copper alloys exposed to simulated French Callovo-Oxfordien groundwater (aerated and CO2-saturated solutions) have been evaluated from electrochemical impedance spectroscopy in conjunction with X-ray photoelectron spectroscopy.The kinetic reactions and physical properties of the layers grown on the alloy's surfaces, change versus the Ni content in the alloys and the presence of CO2 in the solution.Nickel alloys retain favourable passive properties in such environments, whereas oxide products on copper alloys are insufficiently protective when formed in the absence of dissolved oxygen in the electrolyte. A maximum addition of 30 wt% of copper in nickel alloys provides good results with respect to corrosion resistance. Electrochemical measurements allow discriminating behaviour between oxide layers maintained by diffusion phenomena through layer and passive films which are maintained from migration phenomena.