Corrosion and Plugging of the Hollow Copper Conductor Caused by CO2 Inleakage: Thermodynamic Analysis and Field Evidence

The corrosion and plugging of the hollow copper conductor caused by CO2 inleakage are increasingly recognized as one of the main threats to the safe operation of the generator in power plants. To guide field operation, it is necessary to reveal the underlying effects of CO2 inleakage on corrosion and plugging. Herein, this issue is studied by combining thermodynamic analysis of the Cu-O-2-CO2-H2O system and failure analysis on a typical case in a nuclear power plant. The results demonstrate that CO2 inleakage triggers the chain reaction of the generation, release, and selective redeposition of copper corrosion products. The leaked CO2 accelerates the copper oxidation rate by reinforcing the cathode reaction of the O-2 reduction. Further, due to acidic dissolution and phase transformation caused by the CO2, the oxidation layer is damaged and released into the cooling water. In the failure case, corrosion products in the form of loose clusters and malachite are found. Worst of all, the CO2 markedly aggravates the selective redeposition of the released corrosion products in high-temperature regions. In the failure case, the deposition at the conductor outlet with a higher temperature is much more severe than that at the inlet. This study provides insights into the negative impacts of CO2 inleakage on corrosion and plugging of the hollow copper conductor, which can serve as the theoretical basis for field operation.