Corrosion failure analysis of hollow copper coil used in generator internal cooling water system operated at low-oxygen/neutral water chemistry

This paper reports the corrosion failure analysis of hollow copper coil used in generator internal cooling water (GICW) system operated at low-oxygen/neutral water chemistry in a nuclear power plant. Optical microscope, 3D surface profiler, SEM and tube endoscope were used to characterize the surface morphology of the copper coil. XRD, XPS, EDS and TOF-SIMS were used to identify the chemical composition of the corrosion products. The results show that the copper coil is seriously corroded and plugged. The corrosion products are mainly composed of CuO, Cu(OH)(2), Cu2O and CuCO3 center dot Cu(OH)(2). This failure is attributed to O-2 leakage and CO2 leakage during GICW system operation and shutdown. Their negative effects on the system are then revealed combined the thermodynamics analysis and the field evidences. The low-oxygen/neutral water chemistry requires stringently stable GICW water quality condition, whereas it was markedly changed by the leaked O-2 and CO2. Thereby, the passive film was destabilized by phase transformation of the corrosion products and acidic erosion, resulting in the release of copper compound particles and subsequent system plugging. Further, suggestions for the field operation are drawn from this failure analysis. This case study can serve as a warning and a guidance for the safe management of GICW system.