In the operation of JT-60SA tokamak device, such loads as electromagnetic (horizontal and vertical loads of 2.5 MN and 7.5 MN, respectively) and seismic are imposed on the VV, and thermal expansion takes place during the baking of Vacuum Vessel (VV). The nine Vacuum Vessel Gravity Supports (GSs) have to support the loads and total dead weight of 400 tons including in-vessel components and compensate thermal deformation. Assembling to realize precise positioning of each GS to the VV is indispensable in the limited space between toroidal field coils. To meet the design requirements described above, a GS is equipped with an assembly of flexible plates (FPs) in its lower part and a stem in its upper part with external thread that is screwed upward on the internal thread of VV stub for installation. Electric discharge machining is applied to form FPs without welding. Narrow gap TIG and electron beam welding are also adopted to suppress welding distortion. By the FEM analysis-based design and successful product manufacturing, we have established a design concept and manufacturing technology of GS that has both stiffness and flexibility. The installation mock-up test of GS has also successfully finished.

Blankets with a cylindrical structure have been developed for a water-cooled ceramic breeder concept considering a pipe break inside the blanket container. Most existing studies have examined a box structure for the blanket container. Structural change from a box to a cylinder can decrease in first wall thickness while maintaining the pressure resistance of the container. Two blankets with radial and toroidal/poloidal cylindrical axes have been developed. Their first walls are hemispherical and half cylindrical. The tritium breeding capabilities of the developed blankets were studied using Monte Carlo code MCNP5.14. Different combinations of breeder and neutron multiplier materials were considered. With the combination of lithium oxide and beryllium, the tritium breeding ratio of the blankets including surrounding gaps was evaluated as higher than 1.20, leading to a net tritium breeding ratio higher than 1.05.

The JT-60SA superconducting tokamak is being constructed under dual projects, the EU-JA international collaboration framework and Japanese national programme. To suppress magnetic field error to less than 0.01% with respect to the toroidal magnetic field for good confinement of plasma, QST has developed a precise onsite assembly technology of tokamak components such as vacuum vessel (VV) and toroidal magnetic field coils (TFC) with size of over 10-m scale. Prior to an onsite assembly, the assembly process is carefully simulated in a three dimension CAD model, through which the location and number of the reference points for the assembly are evaluated to determine each component position. In the onsite assembly, the tokamak components are positioned by measuring with the laser tracker of a 0.5 mm spatial resolution and assembled by adjusting with shims and splice plates. The onsite assembly of the VV 340 degrees sector has been succeeded in an allowable accuracy of +8/-4 mm with the 10 m diameter by welding sectors, each of which was circumferentially segmented and manufactured by taking into account the deformation due to the welding. The remaining 20 degrees sector will be installed after the TF coils installation. The metrology developed for the onsite assembly of the JT-60SA is expected to be applicable to ITER whose size is the double of JT-60SA.

Mitsuru Ejiri, Kazunori Kitamura, Takao Araki, Junji Ohmori, Shiro Asano, Atsuro Hayakawa Yusuke K. Shibama, Kei Masaki, Akira Sakasai 江尻 満, 喜多村和憲, 荒木隆夫,大森順次,浅野史朗,早川敦郎, 芝間祐介、正木 圭、逆井 章 Toshiba Corporation,8, shinsugita-cho, isogo-ku,Yokohama, 235-8523, Japan, Japan Atomic Energy Agency, 801-1, mukoyama, Naka , 311-0193,Ibaraki, Japan 株式会社 東芝, 〒235-8523 横浜市磯子区新杉田町8 独立行政法人 日本原子力研究開発機構, 〒311-0193 茨城県那珂市向山801-1

The real vacuum vessel (VV) manufacturing of JT-60SA has started since November 2009 at Toshiba. Prior to starting manufacturing, fundamental welding R&Ds had been performed by three stages. In the first stage, primary tests for screening welding method were performed. In the second stage, the trial welding for 1 m-long straight and curved double shell samples were conducted. The dependences of welding quality and distortion on the welding conditions, such as arc voltage and current, setting accuracy, welding sequence, and the shape of grooves were studied. In addition, welding condition with low heat input was explored. In the last stage, fabrication sequence was confirmed and established by the trial manufacturing of the 20° upper half mock-up [1]. This paper presents the R&D results obtained in the first and second stages.