Design and analysis of the CFETR cryostat

Cryostat is one of the most important systems of the China Fusion Engineering Test Reactor (CFETR) which is a next-generation device in the China fusion research roadmap for the realization of fusion energy. It is a large vacuum tight container (outer diameter: 38 m, height: 39.6 m) that provides 10−4 Pa vacuum environment for the superconductor magnet system and thermal shield system, which will be operated at 4.5 K and 80 K, respectively. The cryostat encloses the entire basic systems of the tokamak and must support all types of load, including gravitational loading, electromagnetic forces, and seismic loads generated from other components and itself. The CFETR cryostat comprises a dome-shaped top lid, two cylindrical sections with circumferential stiffening ribs, a bottom base section, a bottom pedestal, and a support. It is mainly made of stainless steel (SS) 304 L/304. Based on the design requirements, the cryostat has sixteen ports at the top, six ports in the middle, and sixteen ports at the bottom, respectively to provide penetrations for heating, vacuum-pumping, diagnostic, maintenance, etc. In this paper, motivation and main technical parameters of the cryostat are described. Interfaces between the cryostat and other systems are generally presented. Structural analysis, seismic analysis and buckling analysis have been carried out in the normal and abnormal operation cases. The external vacuum cryostat and the vacuum vessel are connected through the bellows in order to absorb relative displacement between them. In addition, the strength check and fatigue life assessment of the bellows of the cryostat are also carried out at the same time. Results live up to the expectation and a technology foundation will be laid for the future construction of the cryostat.