Effect of bentonite form on the corrosion behavior of copper for high-level nuclear waste disposal canister

The corrosion of copper as the disposal canister material was related to the form of bentonite in the deep geological repository (DGR). The corrosion behavior was investigated by the electrochemical tests, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) in a 0.1 mol/L NaHCO 3 + 0.05 mol/L NaCl + 0.05 mol/L Na 2 SO 4 solution. The results reveal that although bentonite can restrict oxygen diffusion, it accelerates copper corrosion in the short term due to the dissolved anions. In the top supernatant, corrosion-induced aggregation and detachment of bentonite lead to the decrease of its barrier property. However, the resulting increase in the corrosion rate promotes the formation of corrosion products, which ultimately protect the substrate from further corrosion. In the bottom slurry, local aggregation of the thicker bentonite layer does not fully compromise its barrier function. The corrosion products remain influenced by oxygen transport and exhibit a composition different from that formed in the supernatant. After copper immersion in the bentonite environment, a mixed layer composed of corrosion products and bentonite particles was observed on the surface. XPS results confirmed the presence of CuO, Cu 2 O, SiO 2 , silicates, Al-silicate, and Al 2 O 3 in this mixed layer.