On the potentiality of using ferritic/martensitic steels as structural materials for fusion reactors

Reduced activation ferritic/martensitic (RAFM) steels are the reference structural materials for future fusion reactors. They have proven to be a good alternative to austenitic steels for their higher swelling resistance, lower damage accumulation and improved thermal properties. However, irradiated RAFM steels exhibit a low temperature hardening and an increase in the ductile-to-brittle transition temperature, which imposes a severe restriction on reactor applications at temperatures below about 350degreesC. Furthermore, a high density of small cavities (voids or helium bubbles) has been recently evidenced in specimens irradiated with a mixed spectrum of neutrons and protons at about 300degreesC at a dose of 10 dpa, which could affect their fracture properties at intermediate temperatures. The upper temperature for the use of RAFM steels is presently limited by a drop in mechanical strength at about 500degreesC. New variants that can withstand higher temperatures are currently being developed, mainly using a stable oxide dispersion. This paper reviews European activity in the development of RAFM steels.