Validation of Fabricability for ITER TF Coil Structures

The ITER superconducting magnet system consists of 18 Troidal Field (TF) coils, 6 Central Solenoid (CS) modules, 6 Poloidal Field (PF) coils and 18 Correction coils. The Japan Atomic Energy Agency (JAEA), acting as the Japan Domestic Energy Agency (JADA) in the ITER project, is responsible for the procurement of 9 TF coil winding packs (WP), structures for 19 TF coils, (including one spare), and assembly of the WP and the coil structures for 9TF coils [1]. TF coil structures, which support large electromagnetic force generated in TF coils under the cryogenic temperature (about 4K), are the mega welding structures composed of coil case and support structures made of heavy thickness high strength and high toughness stainless steel. JAEA started the study on welding trials for the materials to be used since 2008 and have been demonstrating of full scale mock-up model fabrication for main sub-components since 2010. This paper introduces the results on welding trials and status of full scale mock-up model fabrication before fabricating actual products. Enough weld joint performance was obtained with the base metal of JJ1 (FMJJ1 specified by JSME (The Japan Society of Mechanical Engineers) Code [2] and is developed in Japan) and SS316LN (FM316LN specified by JSME Code), and also their combination using JJ1 filler wire (FMYJJ1 specified by JSME Code and is developed in Japan) by narrow gap GTAW process. Welding deformation such as angular distortion between outer plate and side plates of U-shape segment could be controlled and minimized by using effective restraint jig in trial manufacturing of 1m long leg. Validity of welding technology and manufacturing design are confirmed during full scale mock-up model fabrication. And also investigations such as UT (ultrasonic test) and effective welding process for rationalization have been performed.