Transmutation and induced radioactivity of W in the armor and first wall of fusion reactors

The transmutation and induced activity of W in the armor and first wall of a fusion reactor were calculated for various blanket compositions, taking account of multiple step reactions. Neutron spectra calculated with ANISN showed that the flux of low energy neutrons at both armor and first wall using water coolant is fairly high compared to liquid Li, He gas and FliBe coolants. About 4% of W transmutes to Re for the W armor of all blankets after 10 MWy/ m(2) irradiation and is not affected by the difference in blanket composition. On the other hand, W in the first wall substantially transmutes to Re followed by Os for the water cooled blanket. For the longer irradiation, W was predicted to transmute to Os base alloy. The induced activity of the W armor is hardly influenced by the neutron spectrum, The formation of Re-186m and Re-186 controlling the induced activity of the armor for long cooling times is not significant from the viewpoint of the safety level. (C) 1998 Elsevier Science B.V. All rights reserved.