Manufacturing Status of JT-60SA Vacuum Vessel and the Related Technology of Welding

JT-60SA is a fully superconducting coil tokamak upgraded from the JT-60U, and this paper focuses on the vacuum vessel (VV, 150 tons) design concept with the related technology of welding and its manufacturing status. The design concept is developed from the ASME Boiler and Pressure Vessel Code Section VIII Division 2, and the damage tolerant concept is adopted into the welding part hardly inspected. These weld joints are treated as a partial penetration and residual strength is evaluated in the design process. Consequently, accuracy of VV weld structure is enhanced due to reduction of the welding heat input and also less process of weld work is achieved. The vacuum vessel has been manufactured since Nov. 2009. Welding technology related to the VV is surveyed and developed in three stages; element test, 1-m size trail and 20-degree upper half mock-up manufacture. The welding methodologies are selected from element tests, and then the typical vessel segments as a 1-m size are tested. The welding conditions to control its quality and the distortion are evaluated, and the lower heat input condition is additionally researched. On the basis of these results, the manufacturing sequences are established through the large size trial of the mock-up manufacturing.