Assembly and final dimensional inspection at factory of the JT-60SA Cryostat Vessel Body Cylindrical Section

Abstract

The superconducting tokamak JT-60SA is currently being assembled at the QST laboratories in Naka (Japan). Within the European contribution in the framework of the Broader Approach, Spain has been responsible for providing JT-60SA cryostat. The cryostat is a large vacuum vessel made up of 304 stainless steel which encloses the tokamak providing the vacuum environment to reduce thermal loads on the components at cryogenic temperature. It must withstand the external atmospheric pressure during normal operation and the internal overpressure in case of an accident. Due to functional purposes, the cryostat has been divided in three assemblies: the Cryostat Base (CB), the Cryostat Vessel Body Cylindrical Section (CVBCS) and the Top Lid. For transport and assembly reasons the cryostat is made up of 20 main parts: 7 making up the CB and 13 making up the CVBCS (including the top lid). The joints between them rely on bolted flanges together with light seal welds, non-structural fillet welds performed from inside and/or outside of the cryostat. The single wall is externally reinforced with ribs to support the weight of all the ports and port plugs and also to withstand the vacuum pressure. The material is SS 304 (Co < 0.05 wt%) with a permeability (μrel) below 1.1. The CVBCS made of a single wall is a stainless steel shell with a thickness of 34 mm. The CB was manufactured and assembled in-situ in 2013, while the CVBCS has been manufactured, assembled, measured by a Spanish company (ASTURFEITO S.A) and delivered to Japan in November 2017. The paper summarizes the assembly and final measurement of the CVBCS at the factory.