Overview of the Belgian Corrosion Programme in the Framework of the Supercontainer Design for the Final Disposal of Vitrified High‐Level Radioactive Waste and Spent Fuel

In Belgium, deep geological disposal was proposed as the solution in principle by a Royal Decree in 2022. A societal debate in 2023–2024 broadly confirmed this option. A new Royal Decree is being prepared to define the staged process for siting and implementation. ONDRAF/NIRAS currently considers disposal in poorly indurated clay as the reference for its R&D programme. The supercontainer concept is being considered as reference design for disposing of vitrified high‐level waste and spent fuel. It establishes an engineered environment around a metallic overpack, ensuring favourable chemical conditions where corrosion remains slow and predictable, thus supporting long‐term safety no specific rock has been selected yet as host for geological disposal in Belgium; the repository design itself is still generic to a large extent. Moreover, future changes in cement formulations may also influence environmental conditions around the overpack. ONDRAF/NIRAS' programme currently aims at understanding the general trends related to the corrosion behaviour of carbon steel in different environments. The development of novel materials for the overpack are also monitored.