Electromagnetic and structural analysis of thin-double-wall vacuum vessel with D-shape cross section of JT-60U

The vacuum vessel of the JAERI Tokamak-60 Upgrade (JT-60U) has a multiarced D-shaped cross section, and an Inconel 625 thin-double-wall structure is used as the main structure of the vessel. The electromagnetic forces introduced by disruption of moving plasma were analyzed by the MATEX code system using a three-dimensional 10° sector model. Structural analyses were also conducted by FEM (finite-element method) code systems. A three-dimensional fine-meshed model of a 20° sector was used for static stress analyses and dynamic response analyses. In this model, the thin double wall was changed to a single shell with the equivalent anisotropic stiffness calculated by FEM analyses. Local stresses of the thin double wall were analyzed with zooming models, and fatigue life was evaluated and confirmed by comparing the results of the FEM analyses and fatigue life experiments. The average dynamic factor (i.e. ratio of the dynamic result to the static result) was about 1.5 for stresses and reaction forces at supports. Based on the analyses and evaluation, the integrity of the JT-60U vacuum vessel was determined, and the results are reflected in the structural design and fabrication of the vessel