Progress in DEMO design study and issues

Tobita, Kenji

Status of DEMO design conducted under the Broader Approach Activity is reported highlighting on Japanese design activity. Remote maintenance is one of the most critical design issues in DEMO in that a reasonable plant availability needs to be attained in severe radiation environment. Recent design study revealed that the application of "sector maintenance" scheme to a medium size DEMO with a major radius of about 8 m would lead to increase in the size of toroidal field coils, the required current of poloidal field coils and the sector weight. For this reason, "banana-type segment" scheme is under study instead of the sector scheme. In order to resolve diverter heat removal problem, use of copper alloy pipes in high heat flux and low dpa (displacements per atom) zones is under study. Besides, a possible management scenario of radioactive waste produced in periodic maintenance and the resulting waste-related facilities for DEMO are presented.