ITER, knowns as International Thermonuclear Experimental Reactor being proceeded under an international project. The toroidal field coil (TF coil), one of main components, is high-nitrogen 316LNH stainless steel for use at cryogenic temperature. The D-shaped Radial Plates(RPs) are inserted the conductor of TF coil and the height, width and thickness of one RP are 13m, 9m and 116mm.In the fabrication of RPs, it is necessary to perform joint welding of 116 mm thickness and seal welding of cover plate (CP) after inserting the conductor. For one RP, ten joint welds and a total CP length of 1.5 km are required. High-quality, high-efficiency welding is required for these joints, and the RP is required to be fabricated with high-precision with flatness and profile within 3 mm.In order to realize high-precision assembly, we developed a welding method of laser beam welding and applied it to 38 RPs in charge of manufacturing. Specifically, in the joint welding of RPs, we have established a high-quality welding technology for high-nitrogen 316LNH stainless steel using a high-power fiber laser. Using this technology, the required accuracy, which was difficult to achieve by conventional manufacturing technology due to welding deformation, was realized by laser welding a thickness of 116 mm at the center of the plate thickness of 70 mm from both sides at flat and overhead position, followed by machine TIG welding of the remaining portions from both sides. For seal welding of CPs, a robot welding system was developed, and efficiency was improved by simultaneous welding of multiple CPs while minimizing variations in welding. In addition, in order to suppress deformation, a procedure to minimize welding deformation by utilizing welding deformation simulation was established, and a method to achieve the target accuracy was established. These RPs, with 7 layers stacked, are installed in a TF coil that is also manufactured with high-precision for a large welded structure with a height of about 16.5m, a width of about 9m, and a weight of about 300 tons, a high-precision of less than 1/ 10,000 was achieved.As a result, the quality and delivery time of the TF coil have been secured, and it has greatly contributed to the international project. We will continue to contribute to ensuring stable quality by applying high energy beam welding to large structures such as ITER and nuclear power plants.

Application of High-Precision Assembly Technology for Large Structures by Laser Beam Welding

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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