COMPREHENSIVE SAFETY ANALYSIS CODE SYSTEM FOR NUCLEAR-FUSION REACTORS.3. EX-VESSEL LOCA ANALYSES CONSIDERING PASSIVE SAFETY

Ex-vessel loss-of-coolant accidents (LOCAs) in a fusion reactor have b een analyzed to investigate the possibility of passive plasma shutdown . For this purpose, a hybrid code of the plasma dynamics and thermal c haracteristics of the reactor structures, which has been modified to i nclude the impurity emission from plasma-facing components (PRCs), has been developed. Ex-vessel LOCAs of the cooling system during the igni tion operation in the International Thermonuclear Experimental Reactor (ITER), in which graphite PFCs were employed in conceptual design act ivity, were assumed. When double-ended break occurs at the cold leg of the divertor cooling system, the copper cooling tube begins to melt w ithin 3 s after the LOCA, even though the plasma is passively shut dow n at similar to 4 s. An active plasma shutdown system will be needed f or such rapid transient accidents. On the other hand, when a small (1% ) break LOCA occurs there, the plasma is passively shut down at simila r to 36 s, which happens before the copper cooling tube begins to melt . When the double-ended break LOCA occurs at the cold leg of the first -wall cooling system, there is enough time (similar to 100 s) to shut down the plasma with a controllable method before the reactor structur es are damaged.