3-D Thermal-Hydraulic Modeling an in-Cryostat Loss-of-Coolant Accident From a Superconducting Magnet

Accidental transients in superconducting magnet systems for tokamak fusion reactors require thorough analysis, as they can jeopardize the integrity of critical, expensive, and often irreparable components like Toroidal Field (TF) coils. The in-cryostat Loss-of-Coolant Accident (LOCA) is particularly critical among these scenarios. This event is triggered by the release of pressurized Supercritical Helium (SHe), a phenomenon observed in experimental facilities, including ITER Central Solenoid Module (CSM) testing and JT-60SA commissioning. The SHe is discharged into the vacuum cryostat, forming an underexpanded supersonic jet; this rapid expansion results in a multiphase jet comprising supercritical, vapor, and liquid phases. Assessing potential magnet damage and developing diagnostics requires detailed knowledge of the 3D evolution of pressure and temperature distributions. Therefore, a 3D Computational Fluid Dynamics (CFD) model is essential for capturing the complex spatial and temporal dynamics of cryostat pressurization and jet propagation. In this work, a 3D transient analysis of the in-cryostat LOCA is performed, using a simplified ITER CSM geometry. The model simulates the SHe jet propagation from the moment of rupture for several minutes, allowing sufficient time for the module to heat-up. The physical models, especially the multiphase model, are validated against a 2D benchmark problem before application to the 3D scenario. In addition, an Adaptive Mesh Refinement algorithm dynamically tracks the expected shock fronts. Particular attention is paid to the temperature distribution in the CSM, with its evolution monitored from the onset of the accident to the end of the transient.