Effect of Temperature on the Repassivation Kinetics of Crevice-Corroded Nickel Base Alloys

摘要

Nickel alloys containing chromium and molybdenum are candidate materials for the construction of high-level nuclear waste containers. The temperature at the waste containers surface will rise after the repository closure due to the heat released from radioactive decay. After reaching a peak, temperature will slowly decrease. In the present work, we have studied the crevice corrosion repassivation kinetics on cooling, for alloys N06022, N07022 and N10362 in chloride solutions. A two-stage electrochemical test was used. Crevice corrosion initiation and propagation occurred after an incubation period within the first 24 hours of polarization at constant temperature. Then, the temperature was decreased at a certain cooling rate while the potential was kept constant throughout the entire test. Alloy N10362 re-passivated 2-12 K above the theoretical repassivation temperature. Alloy N07022 repassivated 1-10 K below the theoretical value. Alloy N06022 repassivated 10-20 K below the theoretical temperature depending on the testing condition. In general, the repassivation temperature slightly increased as the cooling rate decreased. Extremely low cooling rates are expected in high-level nuclear repositories. Considering the repassivation temperatures determined in the present work, the safety operation conditions previously stated from repassivation potentials as a function of temperature and chloride concentration can be considered conservative.