Effects of Anionic Species on the Polarization Behavior of Copper for Waste Package Material in Artificial Ground Water

The effects of HCO{sub 3}{sup {minus}}, Cl{sup {minus}}, and SO{sub 4}{sup 2{minus}} (Bcar, Clor, and Sulf) on copper as a candidate material for overpacking for geological disposal of high level radioactive wastes are studied at 303 K in dissolved oxygen (DO)-controlled, ground-water simulating aqueous solutions by using a cyclic polarization curve method. Two types of polarization curve were determined: Type A in which free corrosion proceeds in the active dissolution mode, and Type Pin which passivation takes place in a potential domain characterized by a potential that corresponds to Eb, the potential at which the passivated film is broken. Polarization dependence on DO was also determined: when only Bcar is present, a Type A curve results for CO 3,000 ppm; when DO > 15 ppm, however, a Type P results for Bcar {ge} 10 ppm; when either Clor or Sulf coexists with Bcar, Bcar promotes passivation while Clor and Sulf promote active dissolution, the influence of Clor being greater than that of Sulf if Bcar content is constant. The presence of either Clor or Sulf over 100 ppm makes the curve Type Amore » irrespective of DO, both species shifting Eb toward the less noble direction. The constant potential test shows that the passivated film of copper is easily broken if Clor is present.« less