Fitting the vacuum vessel sectors like a jacket, lining the inner wall of the cryostat, or covering the sides of vertical coil gravity supports, ITER's thermal shield panels act as a barrier preventing heat transfer to the ultra-cold superconducting magnets. Thermal shield panels cover a surface of approximately 4,000 m² and are actively cooled by way of a network of small-diameter pipes welded to their surface. In November 2021, tiny cracks were identified in the piping of three yet-uninstalled vacuum vessel thermal shield panels. Considering that the issue could be systemic, the decision was taken to remove and replace all cooling pipes (23 kilometres in total) and, in some cases, opt for a new attachment technique. Two years and a few months later, a lot has already been achieved. Of the nine "assembly units" of vacuum vessel thermal shield (each comprising one inboard and two outboard segments), two sets were sent to India for repair by ITER Organization contractor INOX-CVA. The first panels are travelling back to ITER and, in December, a contract was signed for the repair of three additional units. "At INOX-CVA, the piping is removed, the panel surface is machined, and new piping is welded," explains Chang Hyun Noh, the acting leader for the ITER Vacuum Vessel Thermal Shield and Cryostat Project. "During the machining process, the original silver coating is removed from under the pipe path. This eliminates the need for the chlorine rinsing that contributed to the stress corrosion cracking problem."In order to mitigate the risk of panel deformation due to the removal and re-welding of the cooling pipes, the ITER Organization has asked a Korean company, SamHong Heavy Machinery, to manufacture two additional vacuum vessel thermal shield assembly units. Ultra-high polishing of the panels' surface, rather than silver coating, will simplify the manufacturing process while ensuring "similar performance" in terms of thermal emissivity. Acting as a barrier preventing heat transfer to the ultra-cold superconducting magnets, thermal shield panels cover a surface of approximately 4,000 m². Replacing 23 kilometres of cooling pipes requires specific approaches that depend on the nature and accessibility of the different thermal shield components. Meanwhile, in the partly vacated poloidal field coil winding facility on site, the remaining sets of vacuum vessel thermal shield are being inspected and tested for corrosion cracking. Only the panels without the presence of deep ongoing corrosion cracking, namely with very small and superficial defects, are being shipped for repair in India," says Chang Hyun.Last year, the support thermal shield panels, which provide a thermal barrier to the 18 toroidal field coil gravity supports, were removed from the machine assembly pit. Their relatively low weight (730 kg per unit) and simple, rectangular shape, make them easier to deal with. Piping was removed from the panels, and they were sent for machining to a contractor near Lyon, France. Once machining—a process that removes approximately 2 mm of material—is complete, the panels will be returned to ITER and new piping will be welded under the responsibility of ITER TAC-1 assembly contractor, CNPE.The lower cryostat thermal shield, which was installed in January 2021, presents a more daunting challenge. Due to space and cleanliness constraints inside the assembly pit, removing and re-welding cooling pipes has been ruled out. Instead, a new set of piping will be clamped to the component's surface. However, as long as poloidal field coils #5 and #6 remain in their present, temporary position, part of the lower cryostat thermal shield is inaccessible. Repairs will be finalized only when the coils are lifted into their final position. Once repaired, and in a few cases re-manufactured, vacuum vessel thermal shield panels will be reassembled with vacuum vessel sectors and toroidal field coils to form the modules that, once joined, constitute the doughnut-shaped plasma chamber. Other parts of the machine's thermal shield—for example the equatorial and upper cryostat thermal shields that were delivered in 2021 and are currently stored by ITER's global logistics provider DAHER in a large warehouse close to Marseille's industrial harbour—will be preventively repaired. Technical specifications are under preparation, reflecting lesson learned from vacuum vessel thermal shield repair and a call for tender will be launched soon.Chang Hyun aims to have support thermal shield repair finalized by early 2025 and vacuum vessel thermal shield repair finalized by the first quarter of 2026. As for the lower cryostat thermal shield, the schedule is dependent on the repositioning of poloidal field coils #5 and #6 once all 18 toroidal field coils are in place.

A thorough review of all "in-vessel" assembly scope was organized by the ITER Machine Assembly Program in early February, with the active participation of senior management. The review provided a panoramic view of the assembly tasks that will be carried out on the inside of the vacuum vessel, diving deep into the complexity and scale, the sequence and logic, the tools and infrastructure, and identifying technical and schedule-related opportunities and risks. ITER in-vessel assembly begins after the nine sectors of the ITER vacuum vessel have been aligned and welded together and teams can start installing the captive components inside the vessel required for the first phase of ITER operation—AFP, or Augmented First Plasma, as described in the new baseline plans that are under elaboration by the ITER Organization and the Domestic Agencies. The scope of in-vessel assembly includes tens of thousands of individual tasks. Diagnostic looms, loops, magnetic sensors, thermocouples, connectors, feedthroughs, waveguides, cables, and instrumentation; pipe-based pellet and gas injection systems; ELM and vertical stability in-vessel coils; blanket manifolds and blanket modules; diagnostic and heating port plugs; and divertor cassettes—all need to be installed within limited space constraints, according to an optimized sequence, and in good coordination with other engineering teams involved in coactivity. Experience shows that precision and proficiency in executing assembly tasks is critical, particularly given the high volume of repetitive work. For example, approximately 1,000 sensors must be installed per vacuum vessel sector, while for the plasma chamber overall, 18 km of cables—housed in 99 looms—are supported by 9,000 clamps. The importance of commencing qualification well in advance of all processes and ensuring thorough training for operators was highlighted by review participants. Other specific challenges such as the limited time available for the customization of components, limited clearance, and tight assembly tolerances are being addressed through comprehensive test and qualification programs and mockups. The installation of diagnostic sensors—and corresponding thermocouples, connectors, loops, coils, cables and looms—is only one of the challenging in-vessel assembly tasks ahead. As an example of a schedule-related opportunity, the group reviewed a set of purpose-built tools that is being planned to facilitate and optimize the assembly of the ITER blanket system and to allow for an earlier start for the installation of divertor cassettes. The blanket assembly tools are designed to facilitate co-activity in the vacuum vessel during critical phases, streamline the installation process and optimize resource utilization. In addition, the tools will be re-used in later assembly phases after upgrading to meet next-phase requirements. Recognizing the essential role that metrology will play during the in-vessel assembly period, the review group mandated a fully developed metrology plan for the full in-vessel scope. A significant quantity of data must be processed for reverse engineering and the custom-machining of many system interfaces and supports in a short period of time. Additionally, participants emphasized the need to consider the intricate interaction between in-vessel and in-port works. Co-activity must be carefully considered, with the early anticipation of work interruption and robust protection measures to prevent possible component damage from subsequent activities. In conclusion, the ITER in-vessel assembly represents a monumental engineering endeavour, requiring excellent preparation and planning, coordination, execution, and schedule and cost management. A comprehensive approach, addressing challenges and mitigating risks at every stage of the assembly process, will ensure the project's success.

The ITER Organization has opened its 2024 internship program with the publication of 60 offers on the ITER website. These opportunities are geared toward undergraduate and postgraduate students, with a broad array of topics across scientific, technical and support departments. Applicants must hold a passport from one of the countries participating in the ITER Project (the People's Republic of China, the European Union, India, Japan, the Republic of Korea, the Russian Federation and the USA).See this page to apply. The deadline for students to submit their application is 17 March 2024. Please note that additional internship opportunities will be launched in May 2024.