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Tokamak Assembly

The size and weight of the major components, the tiny tolerances and careful handling required for the assembly of huge and unique systems, the diversity of manufacturers, the tight schedule, complex interfaces ... all of these elements combine to make the assembly of the ITER machine an engineering and logistics challenge of enormous proportions.

These contractors are carrying out the day-to-day work of machine assembly under the oversight of the ITER Organization:

: CNPE Consortium (China Nuclear Power Engineering; China Nuclear Industry 23 Construction Company Ltd.; Southwestern Institute of Physics; Institute of Plasma Physics, Chinese Academy of Sciences ASIPP; and Framatome). For the assembly of the cryostat and cryostat thermal shield; magnet feeders; the central solenoid, poloidal field and correction coil magnets; and cooling structures and instrumentation. Also for sector module sub-assembly (Stage 2, 2024 -):: assembly of the main vessel and ports, sector sub-assembly with toroidal field coils and vacuum vessel thermal shielding.

: DYNAMIC SNC consortium (Ansaldo Nucleare; Endel Engie; Orys Group ORTEC; SIMIC; Ansaldo Energia; and Leading Metal Mechanic Solutions SL). For the assembly of the main vessel and ports, sector sub-assembly with toroidal field coils and vacuum vessel thermal shielding. (Stage 1, 2019-2024)

VVW2P Contract (Vacuum Vessel Welding Production Phase): ENSA (Equipos Nucleares SA) For the in-pit welding of the main vessel (9 sectors).


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The challenges of machine assembly

Accurate alignment, particularly of the magnet system and in-vessel components, is essential to the successful operation of the machine. Dimensional control will be critical to ensuring that tolerances are respected, and to recording the "as-built" status of the machine, which will be directly compared against ITER's Computer-Aided-Design (CAD) models in order to correct eventual deviations in alignment before they accumulate. Positional tolerances for the largest components, including the magnet coils and the vacuum vessel, are as low as 2 mm. (For more information, see Metrology.)


Vacuum vessel welding

Welding the ITER vacuum vessel and ports inside of the assembly pit will require a little over two years, an estimated 200 technicians, and a host of customized techniques and tools. The welding tools will have to manoeuvre the complex geometry of the sectors and ports and reach areas that are not directly accessible to operators and where visibility is restricted. The robots will also be confined to welding from inside the vessel and ports, as the pre-installed vacuum vessel thermal shield makes access to the exterior surfaces impossible. Extensive trials on mockups have been performed to quantify and plan for shrinkage, and to qualify tools, processes, and inspection techniques. (See related article here.)

ITER will host one of the largest and the most complex high vacuum systems ever built. To ensure correct machine performance, all connections associated with ultra-high vacuum or high vacuum components must be 100 percent leak-tight. Vacuum lines, helium lines, pipes, valves, seals, joints, and/or flanges have all gone through pre-qualification, while some of the largest vacuum components—for example, the seals manufactured for the vacuum vessel's 50+ large ports—are being tested on dedicated test rigs. During in-pit assembly, only qualified welding procedures, carried out by certified professionals, will be employed, and the quality of all vacuum-related welds will be verified by surface and volumetric non-destructive examination. Full-scale leak testing is planned during the 12-month integrated commissioning period before First Plasma, during which the large vacuum chambers—the vacuum vessel and the cryostat—will be evacuated and leak tested. In parallel, the ITER Organization is developing a set of specialized tools and technologies for the localization and detection of leaks smaller than the width of hair divided by one million.

Ultra-high and high vacuum

French nuclear regulations

As the nuclear operator of the ITER installation, the ITER Organization has an obligation to ensure that safety and security standards are implemented and enforced throughout construction, manufacturing, assembly, and operation in compliance with the Host country's safety and security regulations. All activities related to a safety-important or protection-important component or system (for example ITER's first confinement barrier, the vacuum vessel) must be performed correctly and documented as verified through regular surveillance and inspection.

Once delivered to the site, the interfacing elements for a number of large components such as the ITER blanket and the divertor have to be customized to comply with precise alignment requirements. Assembly contractors will have to use dimensional control and reverse engineering to plot out this customization, and must provide the workshop space, tooling and expertise to carry out the work on short timescales. (See related article here.)



The ITER Organization and its assembly partners will be managing a large volume of assembly activities—such as major lifting operations, handling/positioning, mechanical fixation, welding, cabling, pipe work, metrology, non-destructive examination, and leak testing—in the extremely crowded environment of the Tokamak pit and the Tokamak Complex. Close coordination between the activities of the assembly contractors and the teams completing building works contracts in the Tokamak Complex is crucial.

Throughout Assembly Phase I, the ITER Organization will rely heavily on the on-time delivery of components and systems from the seven Domestic Agencies. Any delay related to fabrication or transport risks disrupting the carefully planned assembly sequences, especially for time-critical components such as the magnets or the vacuum vessel sectors.


Setbacks 2022

In November 2022 the project announced that two key machine components required repair. The correction of dimensional non-conformities on three ITER vacuum vessel sectors and the replacement of all cooling pipes on the vacuum vessel thermal shield is already underway; contractors have been selected and a provisional calendar established. Vacuum vessel assembly is paused until repairs and testing are complete; other machine assembly activities, however, are proceeding.