Supercritical water-cooled reactors (SCWR) are promising advanced nuclear systems
because of their high thermal efficiency (i.e., about 45% vs. about 33% efficiency for current
light water reactors, LWRs) and considerable plant simplification. Materials for SCWR must
have adequate corrosion and stress corrosion cracking response. Initial examinations indicate
ferritic-martensitic steels may have excessive oxidation for thin-walled reactor components and
austenitc alloys are susceptible to stress corrosion cracking, with the problem exacerbated by
radiation. Two novel techniques, grain boundary engineering and surface modification, have
shown initial promise in improving performance of both alloy classes in supercritical water.
The promise of these techniques is demonstrated for an austenitic alloy, Alloy 800H, and a
ferritic-martensitic alloy, HT9.