Perspectives on Corrosion in Supercritical Water Environment: Materials and Novel Treatments

Supercritical water is being considered as a cooling medium for the next generation nuclear reactors because it provides for high thermal efficiency and plant simplification.  However, materials corrosion has been identified as a critical problem because of the oxidative nature of supercritical water.  A number of Cr-containing ferritic steels as well as austenitic steels have been evaluated for corrosion in SCW environment at temperatures up to 600°C after exposure durations of up to 1000 hours.  The ferritic steels develop a distinct two-layered oxide structure, consisting of an outer magnetite layer and an inner Fe-Cr oxide spinel layer.  Surface modification was noted to improve oxidation resistance of these steels.  Austenitic steels exhibited a higher oxidation resistance, but in some cases oxide spallation was observed.  Oxide spallation in these steels was mitigated by thermo-mechanical treatments aimed at enhancing the population of low energy grain boundaries.