Dissolution of Iron Oxides on the Carbon Steel under Cathodic Polarization

The most effective method for reduction of radio activity in BWR nuclear power plants is to remove the iron oxide deposits on the coolant pipes. The dissolution behavior of Fe3O4 deposited on the carbon steel were studied in the EDTA solution by means of cathodic polarization method. Dissolution rate of Fe3O4 was constant and dependent on the electrode potential in the lower range of the rest potential of carbon steel. The potential of the highest dissolution rate was -1.25V vs. SCE in the electrolyte of 60°C. Temperature of electrolyte largely affected the dissolution of iron oxide. Logarithm of dissolution rate changes linearily with the inverse of absolute temperature. On the other hand, dissolved gas in the electrolyte also affected the dissolution. Dissolved oxygen caused to reduce the dissolution by the hydroxide film on iron oxide. Dissolved hydrogen slightly promoted dissolution by the Schikkor reverse reaction.