Anaerobic Corrosion Phenomena of Cast Iron and Copper in Artificial Groundwater at Elevated Temperature

Abstract

The material choice for the canister for the deep geological repository of high-level nuclear waste is a crucial aspect for long-term safety of the repository. In the presented study, the impact of salinity of water in a bentonite slurry on the corrosion behavior of cast iron with spheroidal graphite and copper was investigated. The metal coupons were exposed under anoxic conditions at 60°C for 4 months in a bentonite suspension prepared with artificial water representing Opalinus clay pore water chemistry with different salinity and a water with hydrochemistry from a crystalline host rock in Germany. Light-optical microscopy, µ-Xray fluorescence, X-ray diffraction, µ-Raman spectroscopy and scanning electron microscopy was applied to investigate the corrosion mechanisms on varying length scales. After exposure, cast iron with spheroidal graphite shows an increase in material degradation with higher salinity of the artificial water. The thickness of the Cu₂O layer increases with lower salinity. Despite the difference in material chemistry, the results suggest a general dependence of the corrosion process on salinity of the electrolyte in a bentonite slurry.