SynopsisA study explores the chemical changes occurring between S235JR carbon steel and CEM II/B concrete under water-saturated, anoxic conditions at 80°C, simulating conditions for the disposal of high-level radioactive waste. The research reveals that uniform corrosion processes lead to the rapid passivation of carbon steel, with magnetite identified as the primary corrosion product. While temperature increases and chemical alterations in the concrete were observed, they did not significantly affect the passivation process. These findings are promising for the long-term safety of disposal containers under such conditions, reports NatureArticleIn the realm of radioactive waste management, ensuring long-term safety is paramount. Deep geological repositories (DGRs) have emerged as the preferred solution for the final disposal of high-level radioactive waste. These repositories rely on multiple barriers, both natural and engineered, to safely isolate radioactive materials. One critical component of the engineered barrier system (EBS) is the waste container, designed to withstand the test of time.In Hungary, a DGR is being planned in the Boda Claystone Formation (BCF), and the interaction between carbon steel (C-steel) containers and CEM II-based concrete is a key concern. This concept involves low-carbon steel containers encased in cylindrical concrete buffers and is vital to the Hungarian national waste disposal program.The study aims to investigate the corrosion of C-steel in contact with CEM II-based concrete at a high temperature of 80°C, which simulates geologic disposal conditions. The choice of materials, S235JR carbon steel and CEM II/B concrete, aligns with Hungarian disposal concepts but has broader implications for disposal systems worldwide.The experiments revealed a uniform corrosion process that led to the rapid passivation of C-steel cylinders. Remarkably, magnetite emerged as the primary corrosion product, even after only three months of exposure to the simulated conditions. This passivation process is crucial for the long-term integrity of waste containers.Modeling supported these findings and demonstrated that while temperature increases led to changes in sulfate concentration and slight shifts in pH and chloride concentrations at the cement/steel interface, these variations did not significantly impact the passivation corrosion process. Furthermore, the study considered the thermodynamic possibility of Fe-siliceous hydrogarnet formation at 80°C but found that it did not interfere with magnetite passivation.ConclusionThis research offers promising insights into the corrosion and passivation of C-steel containers in high-temperature concrete, a crucial aspect of radioactive waste disposal. The ability to maintain passivation under these conditions enhances confidence in the long-term safety and integrity of disposal containers. Further investigations will build upon these findings to ensure the robustness of disposal systems in deep geological repositories.