Low activation austenitic Mn-steel for in-vessel fusion materials

Several compositions of austenitic manganese steels (Mn-steels) were investigated for in-vessel component materials in D-T fueled fusion reactor with respect to radiation exposure and waste disposal management. The 24.5Mn-13.5Cr steel was developed in which undesired impurities, such as Ni, Mo, Nb and Co, were controlled and C (∝0.025wt%) and N (∝0.22wt%) contents were well adjusted for corrosion resistance and weldability. Experimental observation has shown that this steel has a single γ-phase structure and good properties for vacuum vessel almost the same grade as type 316 stainless steel (316SS), such as low permeability, good weldability, good mechanical properties of strength and toughness and good corrosion resistance. Activation calculations were performed adopting this material for the JT-60 Super Upgrade (JT-60SU) vacuum vessel and the effectiveness of low activation was confirmed. (orig.)