GALVANIC CORROSION BETWEEN THE NUCLEAR WASTE DISPOSAL CONTAINER MATERIALS COPPER-NICKEL ALLOYS AND CARBON STEEL IN SALT BRINES

摘要

In the present work, the galvanic corrosion of the candidate disposal container material pairs Cu-Ni 90-10/TStE355 carbon steel and Cu-Ni 70-30/TStE355 steel (contact specimens), respectively, has been investigated in two disposal relevant salt brines at 150 deg 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 indicate that in the 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 MgCl_2-rich Q-brine, however, both in unirradiated and irradiated environment 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 carbon steel and significant increase of 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 MgCl_2-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 carbon steel.