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

Reduced activation ferritic/martensitic (RAFM) steels are the reference as structural materials for the future fusion reactors. They have proven to be a good alternative to austenitic steels for their higher swelling resistance. However, RAFM steels exhibit irradiation-induced low temperature hardening and increase in the ductile-to-brittle transition temperature, which imposes a severe restriction on their reactor applications at temperatures below 300 deg C. Furthermore, a high density of small helium bubbles has been recently evidenced in specimens proton-irradiated at about 300 deg C to a dose of 10 dpa, which could affect their fracture mechanical behavior at intermediate temperatures. Their temperature window of use is presently limited by a drop in mechanical strength at about 600 deg C. So, new variants that can better resist at high temperatures, are currently being developed, mainly using a stable oxide dispersion. The potentiality of using present RAFM steels and the variants being developed for the first wall of future fusion reactors are reviewed below. (author)