Study of safety concept for a helical-type fusion reactor, FFHR

Safety concepts for a force free helical reactor (FFHR), of which conceptual designs have been studied in parallel with the construction of the large helical device (LHD), are presented. The main safety features expected for the FFHR are, steady-state plasma operation, no dangerous current disruptions, and the selection of a molten-salt Flibe blanket for a tritium breeder which has low tritium inventory, self cooling effect and low chemical activity. The blanket reaches such high temperatures that the tritium permeation rate increases and this tritium must be continuously recovered. Then the first wall is expected to have a low tritium inventory. Based on the classification of the plant systems and components, it is shown that the high mobility and large radioactivity release accident accompanied with the energy release is avoidable. Fundamental safety would be secured by multiple protection systems. To prevent escalation to a severe accident caused by the fracture of any of the large radioactivity confinement components, passive and reliable active protection systems are proposed. Thus, FFHR will be designed to be as safe as possible.