The localized corrosion behavior of austenitic stainless steels UNS S31603 and UNS N08904 was evaluated in solutions containing chloride, sulfate, and thiosulfate at near-neutral pH simulating deep geological clay environments. These stainless steels are considered as candidate container materials for the final disposal of high-level nuclear waste for the Belgian repository concept in an underground clay environment. Cyclic potentiodynamic polarization measurements were used as an electrochemical technique to compare the pitting behavior of the tested stainless steels. The experiments were conducted at 16 and 90°C in oxidized synthetic interstitial Boom clay water with varying sulfate concentrations of 216 and 5400 mg/L, chloride concentrations ranging from 100 to 10000 mg/L, and thiosulfate concentrations ranging from 2 to 200 mg/L. The surface of each specimen was investigated by Optical Microscopy and Scanning Electron Microscopy after electrochemical
testing. Pitting is initiated more easily with increasing temperature. Increasing the chloride concentration lowers...
Keywords: stainless steel, UNS S31603, UNS N08904, pitting corrosion, polarization, chloride, sulfate, thiosulfate, container materials, radioactive waste, disposal, underground, clay