Corrosion performance of metals for supercritical water, oxidation-utilized organic waste-processing reactors

Corrosion tests were conducted to select the structural material for a reactor to decompose organic wastes generated from nuclear power plants, utilizing the supercritical water oxidation (SCWO) process. Test conditions were based on the decomposition of chloroprene (C₄H₅Cl) and cation exchange resin, which generate hydrochloric acid (HCl) and sulfuric acid (H₂SO₄) in process fluids. In order to select candidate materials, short-period screening tests were carried out on various corrosion-resistant materials in HCl and H₂SO₄ solutions, using static test vessels at 300°C, 400°C, and 450°C. Subsequently, cyclic corrosion tests were carried out for Ta. Ti, and Ti alloys to estimate the corrosion rate and to evaluate their applicability for waste-processing plants. The results of these tests indicate that the corrosion resistance of Ti alloys is sufficient for them to be applied as reactor materials for organic waste decomposition systems using the SCWO process. In this paper, the stability of surface films is discussed using potential-pH diagrams and oxide film analyses. Based on the test results, a bench scale, flow-through-type test reactor and a pilot plant for resin decomposition were designed and constructed.