Comparison of FEM Predicted and Measured Values of the ITER TF Coil Closure Welding Distortion

Abstract

The ITER reactor relies in magnetic confinement of hot plasma. The main driver for the confinement is played by the Toroidal Field Coils. These magnets are composed by a Winding Pack, made of Nb3Sn superconductors, and a surrounding stainless steel structure or Coil Case which is closed by welding once the Winding Pack is inserted. The closure GTAW weld of the cases includes about 70m of weld ranging from 40 to 120 mm. Due to the tight tolerances that have to be respected on the final Toroidal Field Coils, a mechanical quasi-static Finite Element Model has been developed using ANSYS software by Enginsoft and SIMIC, under the work frame of a Fusion for Energy contract, to predict the welding distortion by simulating different welding scenarios and to confirm the definition of the required extra-material in the Toroidal Field Coil Cases. The FEM model was firstly benchmarked with validation coupons, then verified and fine-tuned with four 1:1 scaled Toroidal Field Coil Case cross section mock ups. Finally, a full Finite Element Model has been developed in order to predict the deformation of the cases during the welding process. The first Toroidal Field Coil has been welded during the first half of 2019. In this paper, a comparison between the deformation predicted by Finite Element Model and direct dimensional measurements of the distortions carried out during the welding process is presented.