Corrosion Behavior of NF616 and D9 as Candidate Alloys for Supercritical Water Reactors

Abstract The corrosion behavior of a ferritic-martensitic steel NF616 and an austenitic stainless steel D9 exposed to supercritical water (SCW) at two different dissolved oxygen concentrations, 25ppb and 2 ppm, for exposure times of up to 505 hours at 500°C was characterized. The oxide development and microstructural characteristics of the oxides that formed on the samples were analyzed by measuring weight change, oxide layer thickness, and compositional variation through the oxide layer using a Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopy (EDS) capabilities. The dissolved oxygen concentration plays a significant role in the oxidation behavior of the alloys. Both alloys exhibited much finer oxide particulates in the outer oxide layer under exposure conditions with higher oxygen concentration. For these short time tests, both NF616 and D9 showed a tendency to form a stable, self-protective oxide layer, but for D9 exposed to high oxygen concentration, a severe exfoliation of the outer oxide was observed.