In ITER, the vacuum vessel (VV) is designed to be a water cooled, double-walled toroidal structure made of 316LN stainless steel with a D-shaped cross section approximately 9 m wide and 15 m high. The design work which began at the beginning of the ITER-EDA is nearing completion by resolving the technical issues. In parallel with the design activities, the R&D program, Full-scale VV Sector Model Project, was initiated in 1995 to resolve the design and fabrication issues. The full-scale sector model corresponds to an 18° sector (9° sub-sector×2) and is being fabricated on schedule. To date, 60% of the fabrication had been completed. The fabrication of full-scale model including sector-to-sector connection will be completed by the end of 1997 and performance tests are scheduled until the end of ITER-EDA. This paper describes the latest status of the ITER VV design and the Full-scale Sector Model Project.

Recent design progress of the vacuum vessel for the International Thermonuclear Experimental Reactor is presented. A structural design strategy has been developed for the VV in which the VV will be designed, fabricated, and tested per the requirements of the ASME Code Section VIII, Div. 2. The inboard structure that was originally designed polygonal cylinder has been modified to a cylindrical shape in order to resist the induced forces due to the fast current discharge of the TF coil. The shielding material under the TF coils in the upper outboard region has been changed to a ferromagnetic material (SS 430) instead of SS 30467 to reduce toroidal field ripple. The thermal and hydraulic analyses indicate sufficient heat removal capability from the VV. Although detailed design modifications continue to be made to reinforce areas of high stress and to accommodate interfaces with other systems, problems completing the design from a structural standpoint are not anticipated

Major functional requirements for the vacuum vessel are to provide the first safety barrier and to support electromagnetic loads due to plasma disruptions and vertical displacement events, and to withstand plausible accidents without losing confinement. A double wall structure concept has been developed for the vacuum vessel due to its beneficial characteristics from the viewpoints of structural integrity and electrical continuity. An electromagnetic analysis of the blanket modules and the vacuum vessel has been performed to investigate force distributions on in-vessel components. According to the vertical displacement events (VDE) scenario, which assumes a critical q-value of 1.5, the total downward vertical force, induced by coupling between the eddy current and external fields, is about 110 MN. We have performed a stress analysis for the vacuum vessel using the VDE disruption forces acting on the blankets, and a maximum stress intensity of 112 MPa was obtained in the vicinity of the lower support of the vessel.

The Vacuum Vessel is part of the Tokamak-Basic Machine and provides the primary high vacuum and tritium boundary for the plasma. The vessel is also a major safety barrier and must support electromagnetic loads during plasma disruptions and vertical displacement events (VDE) and withstand plausible accidents without losing confinement. It is made from SS 316 LN and has a water cooled, double wall structure. The minor and major radii of the tokamak are 4.1 m and 13 m respectively, and the overall height is 14.5 m. The total thickness of this structure is typically in the range of 0.45-0.83 m. The inner and outer shells are made of welded plates, 40 mm in thickness. The space between the vessel shells is filled with an array of shield plate inserts which, in combination with the blanket and divertor, provide neutron radiation shielding for the coils. As the principal plasma facing component of ITER, the blanket system must be designed to perform power removal and shielding functions. The First Wall (FW) is the most critical component of the blanket and must be designed to remove the surface heat flux from the plasma, while, in combination with a structurally integral shield, reduce the nuclear effects in the vacuum vessel and protect the superconducting coils from excessive nuclear heating and radiation damage. The first wall is exposed to the 1500 MW fusion power at an average neutron wall loading of about 1 MW/m2 and must be designed for a life of 0.3 MWa/m 2 during the Basic Performance Phase. In addition the First Wall must successfully withstand peaked thermal and electromagnetic loads resulting from plasma disruptions. The total electrical resistance of the vacuum vessel and the blanket structure is approximately 4.5 μΩ to limit the induced eddy current flow while allowing magnetic field penetration