The use and performance of graphite and metal ISSECS in tokamak fusion reactors

Carbon and the metallic elements molybdenum, niobium, vanadium and tungsten have been considered for use as an ISSEC (International Spectral Shifter and Energy Converter) in tokamak fusion reactors. All five materials have been shown to reduce the radiation damage in the 316 SS structural first wall and thus increase the first wall lifetime. On a per unit thickness basis, a tungsten ISSEC is most effective in this regard follwed by Mo, Nb, V and carbon ISSECS in decreasing order. Among the four metals studied, Mo is considered to be the best material for use as an ISSEC. A definitive choice between a graphite and Mo ISSEC is difficult at this time as both materials have strong positive features; carbon being superior from radioactivity, afterheat, cost and fabricability standpoint, but Mo being more effective in reducing the radiation damage in the first structural wall and increasing the energy multiplication in the blanket. (Auth.)