The Effects of Chloride Ion Concentration on the Pitting Behavior of 309L Cladding by Using Micro-Electrochemical Measurement and In Situ Optical Observation

The influence of chloride ion concentration in the pitting behavior of 309L cladding used in nuclear power plants has been investigated in-situ by potentiodynamic polarization and morphology observation using microscale electrodes and ex-situ 2D and 3D geometrical characterizations. The results indicate that the concentration of chloride ion affects not only the pitting potential but also the geometry of the pit. The effects of lowering the chloride ions concentration are to enhance the pit growth in depth rather than width. An extremely low chloride ion concentration (0.001 mol/L) cannot give rise to “normal” pitting corrosion but to a transpassivation-induced pit. The related mechanisms are also discussed.