Effect of Liquid Film Thickness and Flow Velocity on the Cathodic Reaction of Carbon Steel Under Liquid Film Flow Conditions

This study examines how liquid film thickness and flow velocity affect the cathodic reaction rate of carbon steel under flowing liquid film conditions, relevant to the Fukushima Daiichi Nuclear Power Station environment. Liquid film flow equipment was developed, enabling independent control of film thickness (200–1000 µm) and flow velocity (0.3–1.3 m s⁻1). Carbon steel and pure silver electrodes were tested using electrochemical methods to clarify the effects of oxygen transport under different flow conditions. The cathodic limiting current density increased with increased flow velocity and decreased film thickness. However, for carbon steel, the experimental limiting current density associated with changes in flow velocity was different from the theoretical value, mainly because corrosion products formed on the electrode surface. Corrosion products hinder the transport of oxygen, and the increase in flow velocity suppresses the increase in limiting current density. In contrast, the experimental values for pure silver, which does not produce corrosion products, were close to the theoretical values.