In-situ monitoring of the corrosion behavior and impurity enrichment of steam generator tube materials under P W R secondary side thermal hydraulic and heat transfer conditions

A high temperature recirculation loop was developed to simulate secondary side boiling conditions in nuclear power plant steam generators under both normal operating conditions and during impurity, e.g. chloride, transients. In-situ electrochemical impedance spectroscopy was used to study the corrosion behavior and impurity enrichment of steam generator tubing materials as a function of boiling, flow rate and impurity levels. The effect of boiling can be clearly observed in the electrochemical response and in the shape of the pressure-temperature difference curve. Experimental results reveal that boiling contributes to both the surface area of the sample in contact with the solution and increases the corrosion rate. In addition, chloride injections resulted in a further increase in the corrosion rate and, when boiling is stopped, hideout return can be observed and quantified, thus enabling for the correlation between surface-chloride concentration and corrosion rate to be determined. Post-test material and oxide scale characterizations were performed using scanning electron microscope, energy-dispersive X-ray spectroscopy and glow-discharge optical emission spectroscopy after exposure to secondary side thermal hydraulic and heat transfer conditions, along with simulated impurity transients.