Electrochemical study of the pitting corrosion of stainless steel candidate overpack materials for the disposal of high-level radioactive waste in boom clay

The corrosion behaviour in repository conditions is an important factor in the selection of a container material for the disposal of conditioned high-level radioactive waste. To assess the corosion resistance of candidate container materials, electrochemical experiments are performed at SCK•CEN. More specifically, polarisation curves are recorded for eight selected alloys: carbon steel TStE 355, AISI 316L, AISI 316L hMo, UHB 904L, Cronifer 1925 hMo, Hastelloy C4, Ti/0.2Pd, and AISI 316Ti. From these curves, the characteristic pitting potentials E_np and E_pp were derived. The investigated parameters were: chloride concentration, sulphate concentration, temperature, and alloy composition. From the results can be concluded that an increasing chloride content increases the pitting susceptibility of the investigated metals in clay water. A higher sulphate content decreases the pitting susceptibility in clay water. At higher temperatures, the alloys are less resistant to pitting.