Electrochemical properties of carbon steel and low alloy steels in simulated geological disposal environment

Carbon steel is considered to be the most promising material for an overpack container used for the geological disposal of radioactive wastes. In order to know the effect of alloying elements on corrosion resistance in the disposal environment, corrosion mass loss, polarization curves and electrochemical impedance spectra were measured on carbon steel and low alloy steels in compressed bentonite containing simulated bentonite contact water with chloride at pH 8 to 13. It was found that 0.5%Ni-alloying increases but 0.5%Mo-alloying decreases corrosion resistance in the environments. A relatively large dissolution rate was observed on 0.5%Ni-containing steel in the early stage of corrosion. However, the dissolution rate decreased in a short time by the formation of protective film. The dissolution rates of 0.5%Mo-containing steel and carbon steel were smaller than that of 0.5%Ni-containing steel in the early stage but hardly decreased with time. (author)