Long-term polarisation and immersion for copper corrosion in high-level nuclear waste environment

Long-term polarisation and immersion for copper corrosion were investigated in chloride-containing sulphide solutions. Results showed that no active state exists for copper in sulphide-containing solutions, whereas a typical active-to-passive transition exists in the second passivation region, indicating a hydroxyl activation effect on copper. After the sulphide passive film broke down, the pitting area was re-passivated by hydroxide ions; however, if the chloride and sulphide concentrations were both high, then there was no second passivation and the copper would dissolve rapidly. The corrosion resistance and the film thickness both increased with increasing immersion time and an average corrosion rate of 51.2 µm/year was obtained in aerobic solution, which was much higher than in bentonite or under deoxygenated conditions. Moreover, several local corrosion pits appeared after 1-year immersion and this would occur at the beginning of storage.