Conceptual study of maintenance for fusion DMEO reactor toward reduction of radioactive waste

Someya, Yoji; Tobita, Kenji; Uto, Hiroyasu; Asakura, Nobuyuki; Hoshino, Kazuo; Nakamura, Makoto; Sakamoto, Yoshiteru; Tokunaga, Shinsuke

We are considering the reduction of radioactive waste which is generated in every replacement of an in-vessel component such as a blanket segment and divertor cassette for fusion DEMO reactor. Main parameters of DEMO reactor are 8.2 m of major radius and 1.35 GW of fusion output. Maintenance scheme is to replace the blanket segment and divertor cassette independently, as the lifetime of them is different. The blanket segment consists of some blanket modules mounted to back-plate. Total weight is estimated to amount to about 5,630 ton (1,930 ton of blanket module, 3,700 ton of back-plate and 990 ton of divertor cassette). The lifetimes of blanket segment and divertor cassette are assumed to be 3 years and 1 year, respectively, 8,600 ton wastes is generated in 3 years. Therefore, there is a concern that a contamination controlled area for the radioactive waste may increase because much the waste is generated in every replacement. In this paper, management scenario is proposed to reduce the radioactive waste. The back-plates and cassette bodies (628 ton) of divertor was reused. As a result of three dimensional neutron transportation code MCNP, the displacement per atom (DPA) of the back-plates of SUS316L was about 0.6 DPA/3years and that of the cassette bodies of F82H was 1.0 DPA/year. Therefore, reusing the back-plates and cassette bodies would be possible, if re-welding points are arranged under neutron shielding. It was found that radioactive waste in 3 years could be reduced by 68%.