Passivity degradation of nuclear steam generator tubing alloy induced by Pb contamination at high temperature

Effects of Pb contamination on the passivity of a Ni-based alloy (UNS N06690) in a simulated crevice chemistry of steam generator with near-neutral pH at 300 °C are elucidated using electrochemical measurements and surface analysis techniques. The experimental observations reveal that Pb impurity can enter anodic film, which results in substantial changes in the films structure via hindering the dehydration during the passivation and retarding the formation of spinel oxides. The presence of Pb-contamination can also increase hydrogen content in anodic film. Finally, the mechanism of passivity degradation induced by Pb contamination is described on the basis of the experimental data and established theory.