Design and manufacture of the ITER cryostat

The ITER cryostat is a vacuum containment vessel having a very large volume of ~16000 m
³
designed to evacuate to a base pressure of 1×10
^-4
Pa. It is one of the most important and critical systems in the ITER project, providing the function of a vacuum environment for the thermal insulation to the magnet system operating at 4.5K and the thermal shield system operating at 80K. The Cryostat support system design is recently updated and is comprising of the pedestal ring, 18 sliding bearing system, concrete crown support and the skirt support. The cryostat support system is designed to support the ITER tokamak, including both the Vacuum Vessel and the superconducting magnet systems. The entire support system including pedestal ring and skirt support system is categorized as SIC-1 (SIC-Safety Important Components) as it provides the support to the Vacuum Vessel. The ITER cryostat is a fully welded stainless steel cylindrical chamber with top dome shaped lid and bottom flat head. The ASME Section VIII Division-2 is used as a reference code for design, construction and testing of the cryostat. The design and analysis update is done to incorporate the recent project change requirements affecting the building and cryostat support systems, interface design updates affected by changes in the Vacuum Vessel pumping system (Torus Cryo-Pump Housing) and TCWS (Tokamak Cooling Water Systems), regulatory requirements and safety classification of the cryostat support structure. The major challenges involved in the cryostat design and manufacturing are stringent tolerances, code requirements, high vacuum compatible welding of large wall thicknesses, and access limitation for welding, non-destructive examination, and interfaces with a large number of tokamak systems. As the cryostat is huge in size, the limitation on transportation and assembly sequence of the tokamak drives the fabrication stages. The fabrication of cylindrical sections of the cryostat necessitates the huge on-site workshop. The site workshop is being constructed at ITER site. Manufacturing activities such as prototype and welding mock-ups are being initiated by Industry.