Results of ITER Toroidal Field Coil Cover Plate Welding Test

Abstract

Results of ITER Toroidal Field Coil Cover Plate Welding TestNorikiyo KOIZUMI ＊1, † , Kunihiro MATSUI ＊1 , Tatsuya SHIMIZU ＊1 , Hideo NAKAJIMA ＊1Ami IIJIMA ＊2 and Yoshinobu MAKINO ＊2 Synopsis:In ITER Toroidal Field (TF) coils, cover plates (CP) are welded to the teeth of the radial plate (RP) to fix conductors in the grooves of the RP. Though the total length of the welds is approximately 1.5 km and the height and width of the RP are 14 and 9 m, respectively, welding deformation of smaller than 1 mm for local out-of-plane distortion and smaller than several millimeters for in-plane deformation is required. Therefore, laser welding is used for CP welding to reduce welding deformation as much as possible. However, the gap in welding joints is expected to be a maximum of 0.5 mm. Thus, a laser welding technique to enable welding of joints with a gap of 0.5 mm in width has been developed. Applying this technology, a CP welding trial using an RP mock-up was successfully performed. The achieved local flatness, that is, the flatness of the cross-section of the RP mock-up, is 0.6 mm. The analysis using inherent strains, which are derived from the welding test using flat plates, also indicates that better local flatness can be achieved if the initial distortion is zero. In addition, the welding deformation of a full-scale RP is evaluated via analysis using the inherent strain. The analytical results show that in-plane deformation is approximately 5 mm and large out-ofplane deformation, consisting of approximately 5 mm-long wave distortion and a twist of approximately 1.5 mm in the RP crosssection, is generated. It is expected that the required profile can be achieved by determining the original geometry of an RP by simulating deformation during welding. It is also expected that the required local flatness of a DP can be achieved, since out-of-plane deformation can be reduced by increasing the number of RPs turned over during CP welding. A more detailed study is required.