The view from the gangway, 55 metres above the floor of the Assembly Hall, is an ever-changing landscape. The 6,000-square-metre staging area accommodates only two permanent features: the twin sector sub-assembly tools (SSAT1 and SSAT2) designed to assemble the massive vacuum vessel sectors, toroidal field coils and thermal shield segments into sector modules. All around them, the movement of workers, elevated platforms, forklifts, rigging elements and giant components composes a slow-motion spectacle—half mechanical ballet, half construction game. The latest arrival (1) in this view taken on 8 April 2022 is vacuum vessel sector #8, manufactured in Korea and delivered to ITER on 1 April. Like a fossilized alien life form, the component has shed its protective cocoon (2), which now stands empty at the lower left of the image. Close to the newly arrived sector, a toroidal field coil (#9 from Europe), lies in the upending tool (3). Soon, the tool will be moved to its vertical orientation and the magnet coil will be transferred to SSAT1 to be assembled with the second vacuum vessel sector, which has already been equipped with a thermal shield segment (4). A few metres away, SSAT2 holds a close-to-finalized sector module (5), scheduled to be installed in the assembly pit (6) in the coming weeks. To the right of the twin assembly tools, an area (7) is dedicated to the assembly of the US-procured central solenoid modules.  Of the three cylindrical elements, the greenish one is the first module, delivered to ITER in September 2021. The yellow tool to the left is the lifting fixture that will used to move the modules to the assembly platform (grey) and stack them one atop the other in order to form the 18-metre tall, 1,000-tonne central solenoid. The structure along the wall, on the right side of the Hall (8) is part of the support system for the waveguides that will connect the gyrotron sources in the Radio Frequency Building to the tokamak machine. As these lines are being written, the scene in the Assembly Hall has already been transformed, with the house-like cocoon for vacuum vessel sector #8 moved to temporary storage and readied for dismantlement.   

Imagine you have a massive LEGO kit with 1,600 different types of references and you need to build hundreds of one-of-a-kind structures while facing challenging deadlines. Oh, and the kit weighs more than 1,500 tonnes and if a structure isn't perfectly precise, it could result in severe injuries, millions in damage, and weeks of lost time. That, in a nutshell, is the job of the scaffolding team at ITER. "Sometimes it's so complex I get goosebumps," says Roberto Mignone, construction configuration officer and scaffolding contract manager in the Construction Management Office. "Most people don't notice the scaffolding because it is such a common sight, but it's an important backbone of any construction worksite and even more so at ITER." As construction and assembly accelerate at ITER, the demand for scaffolding is increasing. There are currently about 800 scaffolds in use on the site and every month there are more than 300 new scaffolding jobs that need to be done, without considering the modification and dismantling tasks. When most people think of scaffolding, they envision basic facade scaffolding erected to paint a building or work on the roof of a house. At ITER, the scaffolding is used for a broad range of purposes, from providing workers with access to difficult-to-reach areas to shoring up multi-tonne components until their assembly is completed. This means that a scaffolding job can be anything from a 2x2x2 metre platform needed to install a cable tray support, to an immense 50-metre tower for workers installing HVAC systems right below the roof of the Tokamak Building. All of this is the responsibility of ITER's Construction Management Office (CMO), ITER's Construction Management-as-Agent contractor MOMENTUM, and the scaffolding contractor Entrepose Echafaudages. And at the heart of the process is Roberto, who has been working in construction management since 2016. For scaffolding operations in the Tokamak pit, such as this assembly around the central column of the in-pit column tool, a carbon-free kit is necessary. The team now has almost 100 tonnes of carbon-free material on hand after developing and procuring it especially for ITER's needs. "A large part of the job is coordinating the installation," says Roberto. "It is a bit of a puzzle to get the scaffolding erected on deadline without interfering with other assembly activities. That's why so much of our work for the most complex areas is done at night." To manage all the projects, Roberto collaborates with MOMENTUM's four-person scaffolding team and more than 50 other workers from Entrepose Echafaudages. MOMENTUM's Gilbert Mamadou, with more than 30 years of experience, is responsible for the activities in the core of the ITER Tokamak pit. He says the project is perhaps his most demanding mission in term of complexity and coactivity. "I am not building cathedrals, but each structure is a challenge," says Gilbert. "We have a more sophisticated level of scaffolding compared with other worksites. At ITER, there are highly technical zones and components where you need to work with great care for the surrounding items as any impact might have dramatic repercussions on unique components." One of these big challenges came in December 2021 when the Sector Modules Delivery & Assembly Division reached out to Roberto with a critical job: there was no permanent access structure on the first vacuum vessel sector sub-assembly tool (SSAT#1) in the Assembly Building and the contractor needed to reach the upper parts in April 2022. Scaffolding was needed! Imagine you have a massive Lego kit with 1,600 different types of references and you need to build hundreds of one-of-a-kind structures while facing challenging deadlines ... When the order for the SSAT#1 arrived, Roberto activated his on-site team, plus a team of Entrepose Echafaudages designers in Paris. They immediately began working on a 3D model and, after two months of coordination, the blueprints were validated. Then the team started to prepare and deliver the components, which had to meet the cleanliness requirements of the assembly area (parts needed to be brand new or carefully cleaned prior to entering the building). The specially designed scaffold was erected during five night shifts in March 2022 and, after an inspection by Bureau Veritas, it was declared fit for use by the personnel. "The SSAT#1 job was a specific design that shows how flexible you can be with scaffolding compared to a welded structure," says Roberto. Scaffolding projects in the Tokamak pit face another layer of complexity: material. With typical scaffolding made of zinc-coated carbon steel, there is a risk of contamination to the surfaces of the tokamak and rusting; at the same time, aluminium is not robust enough for the load requirements in that area. ITER and the scaffolding provider solved the dilemma by developing a bespoke material, and now almost 100 tonnes of innovative carbon-free scaffolding are available for the cleanest and more complex area of the project. This 28-metre-long scaffolding structure known as "the beam" will be installed above the Tokamak pit to allow for the completion of cable trays and ventilation ducts. ITER's scaffolding needs are "more sophisticated" than at other worksites according to MOMENTUM's Gilbert Mamadou. "At ITER, there are highly technical zones and components where you need to work with great care for the surrounding items as any impact might have dramatic repercussions on unique components." In April 2022, the scaffolding team will face another one-of-kind project; a 28-metre-long scaffolding structure known as "the beam" will be installed above the Tokamak pit to allow the completion of the cable trays and ventilation ducts. For Christophe Jeanmougin, manager for Entrepose Echafaudages on the ITER site, projects like "the beam" and the SSAT#1 scaffolding are what make his job so passionate. "It's hard. We've worked Christmas, holidays, nights ... we sacrifice a lot. But we have committed people and we know how important ITER is, so we are ready to do what it takes as part of the team to reach the necessary milestones."

Some parts of diagnostic systems need to be installed well before the systems are completely designed, creating a challenge in planning. Some components of the ITER machine are referred to as "captive" because, once installed, they become boxed-in by other components or by a built structure and cannot easily be removed. Quite a few diagnostic systems have parts that fall into this category, including systems that have only just passed the conceptual or preliminary design review phase. Because these systems rely on rapidly evolving technology, it does not make sense to freeze their entire design years before the diagnostics will be used. But their "captive" elements must be completed and installed much earlier than the rest of the system. Before installation contracts are awarded, ITER produces an "engineering work package," which is a set of instructions, guidelines and procedures that the contractor will use. Special considerations have to be made for the installation of these captive parts and components. Fortunately, the captive parts are generally not the most sophisticated elements of the systems—they are usually pipes or cables that convey signals back and forth from inside the plasma to the port plugs or places outside of the tokamak where diagnostic analysis takes place using more state-of-the art technology. A good example of captive components is provided by the diagnostic systems that shine lasers and microwaves from outside the Tokamak Building all the way into the vacuum vessel. The beamlines are permanent metal structures, mostly consisting of pipes and supports attached to the gallery ceilings. As other systems are installed under the beamlines, the beamlines become captive. Installation of captive components requires careful planning "The construction team needs to pour concrete very soon to complete the walls around the Tokamak," says Mark Kempenaars, optical diagnostics engineer in the In-Vessel Diagnostics Section, "They need to close holes in the walls, and it means that our paths will be frozen later this year. We will then lose access to these areas simply because other systems need to be installed all around them." Recently installed supports at the L1 level of the Tokamak Building, showing some of the detail of how the supports are bolted to the ceiling by first welding threaded studs to steel plates embedded in the ceiling concrete. This allows for high accuracy in the installation of the optical beamlines. "Installing interfaces for diagnostics systems as captive components takes a great deal of planning," says Kempenaars. "We've produced hundreds of documents and drawings, and spent thousands of man hours for something that probably appears quite simple to someone on the outside." Some of the pipes and supports go through the outer wall of the Tokamak Building—a 1.5 metre-thick, reinforced-concrete structure that acts as an outer container or "confinement barrier" for potentially contaminated air near the machine. Pipes and structures crossing this structure have to be carefully studied and installed exactly as specified to maintain high integrity confinement for the life of ITER. Components mostly arrive as kits. Every support is different but made from similar building elements. Imagine a set of LEGO models where every block is heavy, shiny and hard to identify, except by reading the unique part numbers marked on it and matching them to incredibly detailed drawings. The assembly of these metre-long kits to millimetre precision before they are attached to the building is exacting work and must be executed flawlessly to allow these heavy components to fit in the building correctly and on the first attempt. The first captive systems serve as a model for the rest Installing captive elements of the diagnostics systems has required a change of mind-set. Developers have had to stop following a traditional approach of design, implementation and installation. They now embrace a parallel model, where captive parts of the system are frozen while other parts are still in design. They plan for the parts to arrive within the construction timeline, with built-in margins to avoid cascading delays. Kempenaars is the technical responsible officer for two diagnostic systems, which being at the lowest of the diagnostic levels, serving the divertor region of the plasma, were the first to be affected by the construction tidal wave. To add to complexity, they are in a corner area of the Tokamak Building where there is a lot of interaction with other systems. These systems are among the trickiest to fit, as they have to dodge cable trays and cryogenic lines. Supports installed on the ceiling in the B1 level of the Tokamak Building, showing the "ceiling hugging" nature, which keeps the diagnostic systems very close to the ceiling and above other installed equipment. "Because my systems are the first to be installed, I was the first to have to raise engineering work packages, to get them into the system, to get them approved, to get them manufactured and get the ball rolling," says Kempenaars. "This is how I ended up setting the example." "Now, roughly two-and-a-half years later, we're at the stage where the installation contractor is starting to install system elements into the building and to bolt hardware onto the ceiling for us. Knowing all the work that it took to arrive at this stage, there is incredible satisfaction in the team as they see these steps being taken. It shows that all our planning and coordination have been successful, and serves as a model for subsequent systems."