Optimization of welding distortion of vacuum vessel for nuclear fusion based on finite element analysis

The vacuum vessel (VV) is a crucial part of the Chinese Fusion Engineering Test Reactor (CFETR). 1/8 VV is comprised of two identical 1/16 VVs with symmetrical properties. Welding at a high density between the sectors will affect the overall profile of the structure and may fail to meet the required fit accuracy. In addition, excessive distortion will influence the subsequent assembly of the VV and the degree of the mounting position of the internal components, which cannot be analyzed directly through experimentation due to the scale of the components. Therefore, before welding, a theoretical analysis must be performed to enhance the welding process and reduce welding distortion. In this investigation, welding distortion of plate butt joints in 1/8 VV was simulated using finite element analysis and experimentally confirmed. Local and global welding sequences and welding constraints were studied utilizing distortion curves and clouds. By optimizing the welding sequence, the overall average distortion can be reduced by approximately 13%, and by applying internal constraints, the average distortion can be reduced by approximately 18%, with the greatest change occurring in transverse distortion, which is reduced by approximately 35%. This paper is intended to provide data support and theoretical guidance for the actual processing of CFETR VV using finite element analysis.