Investigation of stress corrosion properties of 9Cr-ODS-Al steel in supercritical water

Abstract

Consideration is being given to the Supercritical Water-Cooled Reactor (SCWR) as a prospective reactor configuration due to its superior thermal efficiency and the simplification of its structure, which obviates the need for steam generators and separators. This has led to the proposition of a supercritical water-based cooling concept within the scope of fusion reactor designs. When selecting alternative structural materials for the fusion breeding blanket, it is imperative to evaluate their resilience against corrosion and their vulnerability to stress corrosion cracking (SCC). In this context, the performance of 9Cr-ODS-Al steel, an oxide dispersion strengthened alloy, was examined under supercritical water (SCW) conditions at temperatures of 400 °C, 550 °C, and a pressure of 25 MPa over a period extending to 1152 h. The analytical findings from SEM and EDS confirmed the formation of a dual-layered oxide on the 9Cr-ODS-Al, consisting of an external layer and an internal compound oxide of Fe, Cr and Al. Slow Strain Rate Testing (SSRT) showed no signs of SCC on the examined fracture surfaces of the alloy, while a decrease in both ultimate tensile strength (UTS) and yield strength (YS) was observed at 550 °C/25MPa. Additionally, the fracture surfaces demonstrated characteristics of toughness, and the growth rate of stress corrosion cracks in the steel escalated with the stress intensity factor.