Creep and fatigue issues for structural materials in demonstration fusion energy systems

The structural materials proposed for use in future fusion energy systems must perform reliably in an environment consisting of intense neutron irradiation, high temperatures, and cyclic stress. Therefore, thermal creep and creep-fatigue (in addition to irradiation creep) are anticipated to be important issues for the engineering design of structural materials for fusion reactors. The key materials systems under consideration for structures of fusion reactors include 8–9%Cr ferritic/martensitic steels, oxide dispersion strengthened ferritic steels, vanadium alloys and SiC fiber-reinforced SiC matrix ceramic composites. The current elevated temperature creep-fatigue design rules based on the American Society of Mechanical Engineers (ASME) code are discussed, along with a brief review of creep-fatigue interaction mechanisms. Refinements to current international design codes to include radiation-induced phenomena such as reduction in uniform elongation have been performed in association with the engineering design of the ITER fusion energy device currently under construction in France. Several other creep-fatigue issues of potential importance for fusion energy applications are discussed.