Low activation ferritic alloys for nuclear fusion reactors

The fusion power reactor concept has an inherent advantage over fission reactor designs; the radioactivity of the fuel decays rapidly with time. However, this inherent advantage will be lost unless reactor structural materials can be employed which have similar advantages. Elemental additions of Nb, Mo, Ni, and N have half lives which will lead to high levels of radioactivity even after 100 years of storage. Therefore, the Office of Fusion Energy, DOE has funded development of low activation alloys, i.e., alloys with very limited additions of Nb, Mo, Ni and N. This paper describes the design and testing of one series of alloys from one of the classes of materials being studied. The alloys are bainitic or martensitic stainless steels which have tungsten and/or vanadium substituted for molybdenum. Alloy selection criterion, production and testing will be described including microstructural examination and mechanical properties testing following irradiation by fast neutrons in a liquid metal cooled fast breeder reactor. The results demonstrate that martensitic stainless steels in the Fe-9 to 12 Cr range appear most promising for fusion structural materials applications