Structural integrity assessment for ITER lower VS coil feedthrough

Abstract

The ITER vertical stabilization coil system is designed to provide fast plasma stabilization in all scenarios with elongated plasma cross-section. It consists of two water-cooled coils located in upper and lower portions of the vacuum vessel (VV), with feedthroughs responsible for the transfer of electricity and cooling water across the vacuum boundary of VV. Depending on location, the feedthroughs can be divided into upper port feedthroughs (UPR feedthroughs) and lower port feedthroughs (LWR feedthroughs), each family sharing the same design. Both designs are subject to demanding operation scheme, a severe working environment and the presence of interfacing components, which impose important thermal, electromagnetic and seismic loads on the components. In particular, the LWR feedthrough, object of present paper, is more impacted by seismic loads due to the more flexible structure compared to the UPR feedthrough. During the worst seismic event, it is subjected to a vertical acceleration of 28.8 m s−2, acting on an effective mass of 249.9 kg at its first order modal mode. Furthermore, the current circulating in the conductor of the LWR feedthrough, impose significant linear forces, up to 27.7 kN m−1 during normal operation and 30.3 kN m−1 during categories I & II abnormal plasma events, respectively. Finally, the effect of differential thermal expansions of interfacing structures imposes a relative displacement between the supports up to 32.9 mm in X (radial) direction and up to 14.67 mm in Z (vertical) direction, during baking. Being part of the vacuum boundary, the feedthrough must assure confinement function under all normal and accidental loading conditions, with proper structural integrity assessment by applying analysis approach and design criteria foreseen by the applicable nuclear codes. The paper details the load types and categories, the analysis methodologies, the structural design criteria, and the assessment results in views of static stress and fatigue for the LWR feedthrough. This study could be a comprehensive reference for the structural integrity assessment of other similar components in fusion devices.