Analysis of a Protected Loss of Flow Accident (LOFA) in the ITER TF Coil Cooling Circuit

In moving toward ITER operation, the detailed analysis of fault conditions for the magnets becomes of increasing importance, to verify that the magnet protection system can safely manage them without any damage to the magnets. A “protected” loss of flow accident in the ITER toroidal field coils, detected by the coil flow meters and managed by the central interlock system, is investigated here using the validated thermal-hydraulic code 4C. We simulate the entire sequence of events that is foreseen to protect the magnet, aiming at verifying the impact on the magnet. The loss of flow accident consequences are investigated in terms of both the temperature margin in the winding pack and of the needed recooling time, which will affect the availability of the machine. It turns out that, for an “accelerated” discharge (i.e., a linear ramp-down) of the magnet current lasting less than 30 min, no quench should occur, while the corresponding recooling time should not exceed 1 h. During the transient, ~10% of the He mass in the coil is vented to the quench tank due to the opening of the safety valves, and requires recooling.