Dynamic simulation of ITER cryo-distribution system using Aspen HYSYS

The ITER cryogenic system consists of the Liquid Helium (LHe) plant, the Cryo-Distribution (CD) system, and the cryo-lines. The Auxiliary Cold Boxes (ACBs) dedicated to cooling the superconducting (SC) magnet system and the Cryoplant Termination Cold Box (CTCB) of the ITER CD system are in the factory acceptance phase. The internal components of ACBs, e.g., cryogenic valves, a cold compressor (CCp), heat exchangers, and a cold circulator (CCr), have been sized and assembled, ensuring their functionality. The interdependency of the functional parameters of one component over the others needs to be assessed, as their integrated performance under the dynamic heat load deposition from the SC magnets may impact the overall operation of the ITER cryogenic system. The ACBs are equipped with two helium baths having ∼ 1200 kg of He inventory and situated inside the Tokamak building. These baths act as a thermal buffer for the LHe plant, situated in the cryoplant building, allowing it to operate at a quasi-steady state despite heat load variation from the applications. Such a large helium inventory can challenge the secondary confinement system of ITER due to helium ingress accidental events and thus needs to be optimized. The integrated system-level simulation is therefore necessary for the safe and reliable operation of the cryogenic system under such demanding requirements. The present study summarizes the results obtained for ACBs dedicated to the magnet system, including CTCB for the enhanced ITER operation modes, and confirms the integrated performance of the system. The results show that the LHe baths inside the ACBs can be used as a thermal buffer with the proposed limit of initial filling and by keeping a constant opening of the respective J-T valves upstream of the LHe baths. The study outcome and the proposed recommendations would be beneficial to mitigate the pulsed heat load to the LHe plant while minimizing the helium inventory.