The ITER fusion energy project in southern France spans a 42-hectare platform with 39 buildings and technical areas, each serving a specific role in operating the world’s largest experimental fusion reactor. Some house the machine itself, others manufacture components too large to ship, and others handle everything from fuel processing to cryogenic cooling. Here’s a breakdown of the most important structures on site.
The Tokamak Complex
The Tokamak Complex is the centerpiece of the entire site. It contains the reactor itself: a massive doughnut-shaped vacuum chamber surrounded by superconducting magnets that confine a superheated plasma at temperatures exceeding 150 million degrees Celsius. The complex includes the Tokamak Building, which sits on seismic isolation pads to protect the machine from earthquakes, and a thick concrete biological shield designed to absorb the intense neutron radiation produced during fusion reactions.
Directly adjacent is the Assembly Hall, a vast workshop where major reactor components are pieced together before being moved into the Tokamak Building. Two 750-tonne overhead cranes run the full length of both buildings and can combine for a lifting capacity of 1,500 tonnes, enough to hoist the heaviest pre-assembled reactor sections into place. Each of the nine steel vacuum vessel sectors, for example, gets fitted with thermal shielding and a pair of toroidal field coils in the Assembly Hall before being positioned inside the machine.
The Cryoplant
ITER’s superconducting magnets only work at temperatures close to absolute zero, and keeping them there is the job of the cryoplant. This soccer-field-sized installation covers a total area of 8,000 square metres, with 5,400 square metres of enclosed buildings and a large outdoor zone for storing helium and nitrogen in both liquid and gaseous forms.
Three cooling units deliver a combined average capacity of 75 kilowatts at 4.5 kelvin (minus 269°C), with a maximum liquefaction rate of 12,300 litres of liquid helium per hour. During operation, nearly 25 tonnes of liquid helium will circulate through a five-kilometre network of pipes, pumps, and valves to cool the magnets, the thermal shield, and the vacuum cryopumps. It is one of the largest cryogenic installations ever built.
The Tritium Building
ITER is the first fusion machine fully designed to run on a 50/50 mix of deuterium and tritium, two heavy forms of hydrogen. The Tritium Building manages the entire fuel cycle: receiving tritium shipments, storing both fuel types, and delivering precise gas mixtures to the reactor through gas puffing and pellet injection systems.
After each plasma pulse, unburned fuel and other gases are captured by cryopumps inside the vacuum vessel, then routed to the Tokamak Exhaust Processing system inside this building. There, hydrogen isotopes are recovered and sent to the Isotope Separation System, which sorts deuterium and tritium for reuse. Leftover waste gas is decontaminated before release. The building also extracts helium-3, a decay product of tritium, from stored fuel supplies. In essence, the Tritium Building closes the fuel loop, recycling unburned fuel back into the reactor while safely managing one of the most tightly regulated substances in the facility.
The Hot Cell and Radwaste Facility
Components inside the reactor become radioactive over time through neutron exposure. When they need repair, refurbishment, or disposal, they are transferred by shielded remote-handling casks to the Hot Cell and Radwaste Facility. This building provides a secure, heavily shielded environment for processing activated components, some as large as a school bus, using robotic systems rather than human hands.
The workflow has two stages. Components first undergo remote cleaning and inspection, then move to areas where hands-on maintenance can be performed safely. The facility also handles test blanket modules, experimental wall panels that will be tested inside the reactor and later returned to partner countries for research. Anything that can’t be reused is classified and processed as radioactive waste.
Magnet Power Conversion Buildings
ITER draws electricity from the French grid as alternating current, but its superconducting magnets need direct current at voltages between 0.10 and 1.35 kilovolts, depending on the magnet. Two identical Magnet Power Conversion buildings act as the adapter between the grid and the machine. They house 44 AC/DC converter units for the project’s first operational phase. Each unit consists of a transformer, a converter, and a busbar section that routes the converted power to the correct magnet system.
Poloidal Field Coils Winding Facility
Four of ITER’s six ring-shaped poloidal field coils are so large, ranging from 8 to 24 metres in diameter, that they simply couldn’t be transported to the site in finished form. Instead, a dedicated on-site factory was built to manufacture them. The Poloidal Field Coils Winding Facility stretches 257 metres long, 49 metres wide, and 18 metres tall, covering 12,000 square metres. Construction of the building itself took from August 2010 to December 2011, and it has since been used to wind, insulate, and test the coils that help shape and stabilize the plasma inside the reactor.
The Control Building
Every system on the ITER platform feeds data back to a central nervous system called CODAC (Control, Data Access, and Communication). The Control Building houses this infrastructure: hundreds of computers organized into functional control groups, monitoring millions of process variables simultaneously. Operators here will manage plasma experiments, coordinate safety systems, and oversee the performance of every major plant system from a single location. The scale of the data network reflects the complexity of the machine itself, with sensors and actuators spread across nearly every building on the platform all routing back to this one facility.
How It All Fits Together
The 39 structures on the ITER platform are not standalone facilities. They form an interconnected system. The cryoplant feeds liquid helium to the magnets inside the Tokamak Complex. The Magnet Power Conversion buildings supply those same magnets with precisely controlled electrical current. The Tritium Building delivers fuel to the reactor and recovers it afterward. The Hot Cell processes anything that comes out of the machine too radioactive to handle directly. And the Control Building ties every signal from every system into a unified operating picture.
As of 2024, ITER reached 100 percent of its construction targets, with most major components delivered and the Tokamak now in its assembly phase. The buildings are largely complete. What remains is fitting the machine together inside them.