Cryostat Pressurization in the ITER plant during an out-Vessel Loss of Cooling Accident Sequence

The paper analyses the pressurization of the ITER cryostat during an ex-vessel loss of coolant accident (LOCA) in the first wall–shielding blanket (FW–SB) primary cooling loop. Since the cryostat is a strong barrier against the release of mobilized hazardous material, its integrity is essential in meeting the ITER safety objectives. The analyses refer to ITER TAC 4 design and were performed by means of a fast running thermal fluid dynamic code that allowed parametric studies. Helium LOCA can be handled by the code, so that the analyses did take into account phenomena such as coil quench and electrical arcing between coil turns, that may occur in tokamaks with superconducting cables in the magnet coils. The main result was that even in the worst conditions the pressure transient in the cryostat does not damage its integrity provided that the plasma facing components (PFC) cooling loops in the vacuum vessel remain undamaged. Hence, if no other energy sources than those coming from an ex-vessel LOCA are added to water, helium and heat structures in the cryostat, the cryostat maintains its integrity. More analyses are needed to evaluate an in-vessel LOCA and the consequent cryostat pressurization transient. In fact this event would add decay heat and exothermic chemical reaction as energy sources to be possibly taken into account in the pressurization transient. These analyses are not within the scope of this work.