Corrosion resistance and material optimization in supercritical water oxidation for radioactive waste treatment

This study addresses the severe corrosion of materials during the supercritical water oxidation (SCWO) treatment of tributyl phosphate (TBP), a key radioactive organic solvent. The corrosion behavior of SS316, Incoloy 800, Incoloy 825, and Inconel 625 was evaluated under oxygen-free, oxidizing, and alkaline conditions in subcritical and supercritical water. Results showed that SS316, although cost-effective, undergoes rapid degradation in oxidizing environments, with a corrosion rate of 1.6 mm/a. In contrast, Inconel 625 maintained excellent corrosion resistance at 0.46 mm/a due to the formation of stable NiCr₂O₄ and Cr₂O₃ oxide layers. Notably, this study demonstrates that phosphate anions derived from TBP decomposition can enhance alloy passivation by forming protective phosphate films. Additionally, alkaline modulation using 1 wt.% sodium hydroxide was shown to reduce corrosion rates across all tested alloys significantly. By coupling corrosion environment control with tailored material selection, a corrosion-resistant SCWO reactor was developed, whose innovative structural design also enhances nuclide separation efficiency, offering valuable engineering insights for SCWO systems.