Cryogenic Aspects of a Demountable Toroidal Field Magnet System for Tokamak-Type Fusion Reactors

Abstract

The toroidal field (TF) coils in a tokamak fusion reactor have to be interlaced with the plasma chamber, OH, and poloidal field coils, and the neutral beam, coolant and vacuum lines, etc., in a very complex arrangement. This makes the construction of the reactor cumbersome since the continuously wound TF coils have to be built on-site first and the rest of the reactor components installed inside the coil assembly afterwards. This creates serious problems of space and accessibility and requires complicated installation procedures for that part of the reactor system inside the TF coil assembly. Figure 1 shows the complicated structures of the ORNL Tokamak EPR design [1]. In addition, the replacement of a failed TF coil after construction would be extremely difficult, if not impossible, which then requires that the TF coil system must be very reliable over its 30-year service lifetime. Replacing a failed TF coil in this type of reactor construction would involve removing and replacing a large number of highly radioactive, massive components with many major cuts and seals to be made. This means a very long plant downtown, even if were technically feasible, reduced plant availability, and large capital losses. Figure 2 illustrates how TF coils will have to be orders of magnitude more reliable than has been demonstrated to date if plant availability is to be above an acceptable limit of ~ 95%.