The development of austenitic stainless steels as low-activity structural materials for fusion reactors

A study based on published information has been performed to examine the feasibility of designing low-activity austenitic stainless steels to replace the conventional steels AISI 316, 320 and 321 and the proprietary steel FV548 for use as first wall and blanket materials in a fusion reactor. The alternative compositions have been chosen subject to the condition that the contact gamma ray dose rate associated with the induced radioactivity does not exceed 2.5 x 10-5 Gyh-1 after a decay period of 100 years. This limit should permit relatively safe handling of discarded components for subsequent recycling. The approach adopted in designing the alternative alloys involved the replacement of the high-activity elements that occur in conventional stainless steels with elements exhibiting low residual dose rates, while at the same time retaining the fully austenitic structure and equivalent transformation characteristics and mechanical properties. The major replacements suggested were Ni by Mn-N combinations, Mo by W, Tb by Ta. (author)