Fig. 2-14 Schematic view of a 1/20 sector of the real size annular vacuum vessel

Fig. 2-15 The half sectors, A and B, fabricated in the factory The half sectors, A and B, were joined by welding, and the final accuracy was within 10 mm.

The vacuum vessel of the fusion experimental reactor, ITER, has an annular radius of around 8 m, its cross section is of D shape, its height is around 15 m, and its width of around 4 m. The wall has a double structure similar to corrugated cardboard to accommodate cooling water pipes. Many parts are assembled and welded, and the finishing accuracy should be within 20 mm. As a part of the ITER technology R&D, we have fabricated the real size vacuum vessel in cross section, and 1/20 sector in azimuth. Furthermore, we have developed a computer code to estimate the dimensional accuracy. An assembly view of the 1/20 sector is shown in Fig. 2-14. Figure 2-15 shows pictures of the fabricated real structures. The dimensional accuracy was 3 mm at this stage. Particular parts were locally shrunk with the metal welding heat, and the size was varied. The shrinkage due to welding was empirically obtained in the actual fabrications and in some local model tests. The results were taken into account in existing computer codes. As a result, we will be able to estimate skillfully the dimensional accuracy of complicated 3-dimensional structures by welding. This kind of achievement will provide one of the fundamental bases for the construction of ITER by international cooperation.

Reference K. Koizumi et al., Fabrication and Assembly of Full-Scale Sector Models for ITER Vacuum Vessel, Fusion Technol., 34 (3, pt2), 586 (1998).

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