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As a participant of ITER project, ITER Korea has to supply two ITER vacuum vessel sectors (Sector #6, #1) of total nine ITER VV sectors. After the procurement arrangement with ITER Organization, ITER Korea made the contract with Hyundai Heavy Industries (HHI) for fabrication of two sectors. Then the start of the manufacturing design was initiated from January 2010. HHI made three real scale R&D mock-ups to verify the critical fabrication feasibility issues on electron beam welding, 3D forming, welding distortion and achievable tolerances. The documentation according to IO and the French nuclear safety regulation requirement, the qualification of welding and nondestructive examination procedures conform to RCC-MR 2007 were proceed in parallel. The mass production of raw material was done after receiving ANB (agreed notified body) verification of product/parts and shop qualification. The manufacturing drawing, manufacturing and inspection plan of VV sector with supporting fabrication procedures are also verified by ANB, accordingly the first cutting and forming of plates for VV sector fabrication started from February 2012. This paper reports the latest fabrication progress of ITER vacuum vessel Sector #6 that will be assembled as the first sector in the ITER pit. The overall fabrication route, R&D mock-up fabrication results with forming and welding distortion analysis, qualification status of welding and nondestructive examination (NDE) are also presented.

The structural analyses of vacuum vessel have been performed to investigate the effect of shell thickness reduction on structural integrity. The finite element models of vacuum vessel considering original design and thickness reduction have been developed. The expected maximum thickness reduction possibly caused by forming and bending processes during fabrication was applied to the curved region of the analysis models. The linear elastic and nonlinear limit analyses have been performed. The structural integrity of main vessel including lower port stub extension has been verified in accordance with the requirements of RCC-MR. It is concluded that the inner and outer shells of main vessel still have enough strength margins under pressure and VDE (Vertical Displacement Event) load conditions in spite of thickness reduction. These results have been reviewed and approved by ITER Organization and ANB (Agreed Notified Body).

A vacuum vessel is one of the core facilities of ITER (International Thermonuclear Experimental Reactor) and basically all-welded structure. Korea is responsible for the procurement of sector 1 and 6 of the main vessel. Accordingly, the design review for the fabrication is in progress by ITER Korea and Hyundai Heavy Industries. Due to anticipated manufacturing problems such as the welding distortion, the design of some components of main vessel, IWS (In-Wall Shield) supporting rib and ELM (Edge Localized Mode) coil support, needs to be modified. To release the risk of welding distortion, the welding method called “bridge type” is suggested and the shape of weld joint is adjusted to secure the manufacturability of the issued components. The elastic and limit analyses with fatigue evaluation have been performed under the most critical loading condition to verify the structural integrity of modified design. Analysis results show that the proposed designs meet the design criteria of RCC-MR. The design deviation requests have been submitted to ITER Organization and ANB (Agreed Notified Body) for approval and their verification is currently in progress.

The ITER vacuum vessel (VV) consists of three main sub-components; main vessel, port structures and the VV supporting system. In this study, the modified designs for the main vessel and the supporting system have been proposed, and the stress analyses have been conducted to investigate their structural integrities. In the original design of the main vessel, the assembling works of the flexible support housing into the outer shell is so difficult that the modified design concept is suggested for easier fabrication. To simplify the VV supporting system for better maintainability and to reduce its fabricating cost, the multi-flexible plates with rigid restraint for the VV support have been proposed. The flexible plate support is surrounded by a rigid restraint with a rectangular cask. As a result of this study, the availability to adopt the modified design concept of the supporting system as well as the main vessel in the ITER VV design has been reviewed.

The ITER vacuum vessel support systems located in the lower level sustain loads in radial and vertical direction. The support system consists of various sub-components like a linkage system, a pot type bearing, a vertical rope, a toroidal constraint, and dampers. In order to examine performance of the mechanism of the system, a mock-up of the linkage system which is comparatively complicated has been manufactured. Various fabrication methods were studied through the mock-up fabrication, and also several tests have been done using the mock-up. Those include assembly study, stroke test, static load test and fatigue test. In the full stroke test, the functional mechanism of the support structure has been demonstrated. In the structural test, the strength of the all components is evaluated by measuring reaction and strain of each component. In order to investigate the effect of tolerances and the damage due to the tests, the performance tests were conducted before and after the static and fatigue tests. The backlash for each stage is found from measured displacement hysteresis. As results of those tests, the performance of the ITER vacuum vessel support structure as well as its structural integrity has been evaluated in this study.

To investigate the structural integrity of the ITER vacuum vessel (VV) and ports, the structural analyses of the regular equatorial and the lower remote handling (RH) ports have been performed. The advanced design of the equatorial regular port adopting a pure friction type flange has been recommended as a reference design by the ITER International Organization. The structural integrity of the equatorial port flange, sealing unit, and connecting duct has been reviewed by conducting nonlinear finite element analyses. The advanced design of the regular equatorial port flange with proper pretension is acceptable in the structural design point of view. From the local analyses for a connecting duct and a sealing unit, it has been found that the stresses are less than the allowable values. The structural analyses of the lower RH port have been also performed to verify the capability for supporting the VV. Since high local stress occurs at the gusset and supporting block, the case study for the lower port has been conducted to mitigate the stress concentration and to modify the component design. The strength of the lower RH port structures can be improved by the design modification of poloidal and toroidal gusset.

Based on the design done by the ITER international organization (ITER-O) and other participant teams, the more detail engineering design of the ITER vacuum vessel port and support is progressed by the Korea ITER project team. In this work, the recent design elaboration and manufacturing feasibility study from 2006 mainly focused on the equatorial and lower port are reported. The fabrication status and test plan of vacuum vessel support mock-up are also introduced.

The international thermonuclear experimental reactor (ITER) vacuum vessel (VV) upper port has a trapezoidal/rectangular cross-section and consists of a port stub, a stub extension and a port extension with a connecting duct. To investigate the structural integrity and to increase the structural reliability of the VV and ports, the structural analyses of the upper port structure have been performed. Two advanced designs from the ITER international team have been deeply analyzed. To verify the strength of the reinforcing ribs for the connecting duct and of the fastening/sealing units, the local analyses utilizing the sub-modeling technique have been performed. The upper port flange based on the original design could withstand design loads, but the flange surface could be detached under the design condition. The advanced design using large superbolts is highly acceptable in the structural design point of view. The deflection of the plug for the other advanced design with a removable flange is relatively large since the stiffness of a port and a plug is reduced by the nut groove and the removable flange.

The Central Solenoid (CS) magnet system of the Korea Superconducting Tokamak Advanced Research (KSTAR) device consists of four pairs of superconducting coils compressed with the CS coil structure. The CS coil structure is operated as a preload structure to give an axial compression on the CS coils. The required axial compression is applied partly by using the pre-compression components in assembly stage and by the thermal contraction difference between the coil winding pack and the structure during cool down stage as well. In order to investigate the structural integrities and to increase the structural reliabilities of the KSTAR CS magnet, global and local structural analyses have been performed for various operation scenarios by developing three-dimensional finite element models. From the analysis results, it has been found that the CS magnet system can safely withstand the reference operation scenarios and the structural integrity of the CS magnet complies with requirements of the design criteria for KSTAR magnet system.