ANALYSES FOR PASSIVE SAFETY OF FUSION-REACTOR DURING EX-VESSEL LOSS-OF-COOLANT ACCIDENT

Passive safety of nuclear fusion reactors during ex-vessel Loss-of-Coo lant Accidents (LOCAs) in the divertor cooling system has been investi gated using a hybrid code, which can treat the interaction of the plas ma and plasma facing components (PFCs). The code has been modified to include the impurity emission from PFCs with a diffusion model at the edge plasma. Wie assumed an ex-vessel LOCA of the divertor cooling sys tem during the ignited operation in International Thermonuclear Experi mental Reactor (ITER), in which a carbon-copper brazed divertor plate was employed in the Conceptual Design Activity (CDA). When a double-en ded break occurs at the cold leg of the divertor cooling system, the i mpurity density in the main plasma becomes about twice within 2s after the LOCA due to radiation enhanced sublimation of graphite PFCs. The copper cooling tube of the divertor begins to melt at about 3s after t he LOCA, even though the plasma is passively shut down at about 4s due to the impurity accumulation. It is necessary to apply other PFC mate rials, which can shorten the time period for passive shutdown, or an a ctive shutdown system to keep the reactor structures intact for such r apid transient accident.