The Development of Castable Nanostructured Alloys for Fusion Reactor First-Wall/Blanket Applications.

Reduced Activation Ferritic-Martensitic (RAFM) steels are proposed as cooling plates and structural materials for first wall/blanket materials in fusion reactors. Conventional RAFM steels have reduced creep rupture strength compared to second-generation FM steels and they have limited upper operation temperature of 550C. Development of advanced RAFM steels targets to increase the creep rupture strength to extend the operation temperature limit. For that reason, we are developing Castable Nanostructured Alloys (CNAs) as the American RAFM steels. The phase fraction of nano-scaled precipitates in CNAs is maximized through optimized composition tailoring and thermomechanical treatments with the goal to improve the high temperature creep strength and radiation resistance. Here, the roadmap of CNAs development will be highlighted, and the microstructure and various properties of interest to fusion applications will be discussed and compared with conventional RAFM steels. Currently a multi-ton scale batch is being procured under the umbrella of an ARPA-E / GAMOW project. Evaluation of the multi-ton scale CNAs will focus on various mechanical properties, weldability, and radiation resistance. The objectives of the scale-up is to demonstrate the production viability, performance advantages and to increase its technical readiness level.