Possibility on the Thermal Quench of the Superconducting Coil at the Loss-of-Coolant Accident

Abstract

Sequential phenomena of fusion reactor at anomaly events, e.g., sudden loss of coolant due to leaks or guillotine breaks at ex-vessel, should be carefully studied before the construction and operation of the fusion power demonstration reactor (DEMO). While a possibility of plasma termination due to impurity ejection from the wall by the loss of its cooling ability is usually considered, there might be a possibility of a plasma disruption induced by the thermal quench of the toroidal field (TF) coil due to the decrease of nuclear radiation shielding performance. Neutronics analyses taken for the Slim-CS DEMO designs with and without coolant water in the shield blanket showed that the nuclear heating rate at its TF coil increases more than 100 times by the coolant loss. Thermal calculation with the calculated heating rates indicated that the TF coil would reach the critical temperature within several seconds. Thus, a passive shutdown sequence other than the impurity from the wall sequence possibly occurs in case of the loss-of-coolant accident (LOCA) by a large penetration of neutrons onto the TF coils, a quench of coil current, and a termination of plasma confinement.