Study on the new manufacture of ITER vacuum vessel thermal shield

Abstract

This paper describes the preparation and the status for the manufacturing of the new Vacuum Vessel Thermal Shield (VVTS) for ITER machine. As the delivered VVTS had the corrosion problem at the pipe weld, the VVTS was determined to be repaired and re-manufactured. The new VVTS has no silver coating and its pipe material is changed to exclude corrosion cracking at the cooling pipe. Roughness of the panel surface is reduced to have lower emissivity without silver coating. Several technical efforts to improve the pipe welding are presented in this paper. Stitch weld between the pipe and the panel is carefully tested with various specimens as Pre-Production Sample (PPS). Tack weld position is intended not to be overlapped with the stitch weld. Back shielding at the opposite side of the stitch weld is also applied to minimize the oxidation. Down-slope current of the welding machine is optimized for the pipe stitch weld. Heat correction method after the welding is investigated to confirm the soundness of the weld joint and the base metal. Impact test and corrosion test are performed for the specimens after the heat correction. All the manufactured VVTS panels are subjected to be leak-tested in a huge vacuum chamber with the pressurized cooling pipe with helium gas. Delivery status of the re-manufactured VVTS panels is presented and the anticipated manufacturing schedule are introduced in this paper.