THE CONCEPT OF DRASTICALLY EASY MAINTENANCE (DREAM) TOKAMAK REACTOR

One of the most important features of a power plant is high availabili ty. An easy maintenance scheme is indispensable for high availability operation. For the easy maintenance scheme, a plasma configuration wit h high aspect ratio (with slender doughnut shape) of about 6 and a sma ll number of 12 torus sectors is introduced. The adjacent torus sector s are jointed mechanically by a bolt-flange structure. The plasma vacu um region comprises a cryostat system and 12 horizontal access doors. A whole section of each torus sector is pulled out horizontally in a s ingle radial straight motion between the adjacent toroidal field (TF) coils. The TF coil system is imbedded in the reactor building and can be repaired independent of the torus structure. The torus structure co nsists of a shield integrated vacuum vessel, a divertor structure and a tritium fuel breeding blanket structure. The divertor or blanket sys tem is replaced from the transverse (toroidal) direction after the tor us structure is pulled out. Even in the torus inboard region, there is a gap of 1 m between adjacent TF coils because of the high aspect rat io reactor configuration. Therefore, all the piping and feeder systems are gathered at the torus inboard region. The overall machine size is determined by a fusion power of 3 GW and almost 100% bootstrap curren t with a moderate Troyon coefficient of 3.5, magnetohydrodynamic safet y factor of 5 and plasma elongation of 1.6.