Galvanic Corrosion Between the Nuclear Waste Disposal Container Material Pairs of Copper-Nickel Alloys and Carbon Steel in Salt Brines

In the present work, the galvanic corrosion of candidate disposal container material pairs of Cu-Ni 90-10/TStE355 carbon steel (CS) and Cu-Ni 70-30/TStE355 steel (contact specimens), respectively, has been investigated in two disposal-relevant salt brines at 150°C, both without gamma irradiation and in the presence of a gamma radiation field of 10 Gy/h (irradiated brine environment only for Cu-Ni 70-30/TStE355 steel). The results of the long-term immersion experiments up to 1.5 years indicate that in the sodium chloride (NaCl)-rich test brine, both with and without gamma radiation, the coupled material pairs form stable corrosion protective surface layers, and, therefore, no galvanic corrosion occurs. In the magnesium chloride (MgCl₂)-rich Q-brine, however, both in unirradiated and irradiated environments, the corrosion surface layers formed on the steel show localized corrosion attack, and, subsequently, galvanic corrosion occurs. This results in localized corrosion on the less noble coupled CS and a significant increase in the general corrosion rate compared to the value of the uncoupled steel specimens. For the more noble coupled Cu-Ni alloys, a clear decrease in corrosion rate is observed in the unirradiated MgCl₂-rich brine compared to the values of the uncoupled specimens. This means that in this brine the Cu-Ni alloys are cathodically protected by the CS.