Aseismatic analysis of ITER vacuum vessel, (1)

Aseismatic analysis of the ITER vacuum vessel was carried out based on the structure designed during the Concept Design Activity (CDA) from 1988 to 1990. A 1/16 sector of the vacuum vessel was modeled and analyzed by using a finite element method (FEM) in order to obtain the vibrational behaviors in the poloidal plane. Also, a simplified FEM model of the torus structure was developed to obtain the behaviors in toroidal plane. This report describes the results and discussion on the aseismatic analysis of the 1/16 sector, the modeling method to simplify the double-skin structure used in the vacuum vessel into orthotropic plates and the aseismatic analysis of the 1/2 torus structure of the vacuum vessel. The major conclusions obtained by a series of analyses are as follows ; (1) The simplified model employing an orthotropic plate as a double-skin reinforced with ribs is useful to represent the vibrational behavior of the vacuum vessel. (2) The natural frequency at the first mode obtained in the analysis of the 1/2 torus structure is about 13 Hz under the free boundary condition of each port and about 50 Hz under the fixed one. (3) The vibrational behaviors at the lower modes are almost dominated by the stiffness of the vessel shell and the mass of the upper port. (J.P.N.)