Effects of Environment on Localized Corrosion of Copper-Based, High-Level Waste Container Materials

Effects of environmental factors on localized corrosion of copper (Cu)-based materials that are candidates for use in high-level nuclear waste containers were examined. Effects of bicarbonate (HCO₃⁻), chloride (Cl⁻), and sulfate (SO₄²⁻), which are present in the ground water near the proposed Yucca Mountain site for a high-level waste repository, were studied. Localized corrosion was observed only at low temperatures in environments involving combinations of high HCO₃⁻ with high Cl⁻ or high SO₄²⁻. Uniform corrosion was observed at low concentrations of HCO₃⁻ (< ∼ 2,000 ppm), especially when Cl⁻ or SO₄²⁻ concentration was high. A passive behavior without localized corrosion was observed at high HCO₃⁻ concentrations at temperatures > 80°C, irrespective of the Cl⁻ and SO₄²⁻ concentrations. Localized corrosion observed in the Cu-based alloys was much shallower than in stainless steels and nickel (Ni)-based alloys and tended to broaden with time under potentiostatic conditions. Oxygen-free Cu (CDA-102, UNS C10200) exhibited a greater tendency toward localized corrosion than a 70% Cu-30% Ni alloy (CDA-715, UNS C71500).