ITER's fusion reactor assembly program relies on an unprecedented fleet of industrial robots, including a future 36-ton machine designed by Larsen & Toubro Ltd. that will dwarf the current record-holder, a 4-meter-tall robot nicknamed "Godzilla." The goal: install nearly 20,000 components inside the tokamak with tolerances as tight as 0.4 mm, working 24 hours a day, 6 days a week, for approximately two years.
The ITER project has long been associated with superlatives. The world's largest experimental fusion reactor, built at Cadarache in southern France under the banner of the ITER Organization, keeps pushing the boundaries of what engineering can achieve. But the latest development in the assembly program goes beyond plasma physics — it lands squarely in the realm of robotics history.
A robot that already holds the title of the world's largest industrial robot is about to be replaced by something three times heavier. And the reason is straightforward: the job demands it.
weight of the future blanket assembly robot, replacing “Godzilla”
"Godzilla" is already a record-breaker, and it's just the test bench
The robot nicknamed "Godzilla" stands 4 meters tall, has a reach of 5 meters, and can lift up to 2.3 tonnes. By any industrial standard, it qualifies as a giant. But within the ITER program, it serves a specific and deliberately temporary role: a test platform for validating the robotic technologies that will eventually work inside the tokamak's vacuum vessel.
Testing before deploying: the logic of full-scale mockups
Starting March 2026, Godzilla begins its testing phase on full-scale mockups of the vacuum chamber. Two large structures have been built for this purpose, each reproducing one third of the tokamak's interior — one located in the former cryostat workshop on the ITER site, the other in a building currently under construction nearby. These replicas allow operators and robots to rehearse every gesture, every interface, every mechanical sequence before a single component is touched inside the actual reactor.
Raphaël Hery, a specialist in robotics for extreme environments cited in the project documentation, underlines the logic: you cannot afford trial and error inside a fusion reactor. The mockups exist precisely to eliminate uncertainty before the real work begins. Robots equipped with advanced vision systems and force and torque sensors will be trained on these structures, learning to detect obstacles, measure resistance, and avoid applying excessive stress on components that cost millions and cannot be replaced easily.
The supplier behind Godzilla's successor
The 36-ton robot that will eventually take over from Godzilla inside the tokamak is being designed by Larsen & Toubro Ltd., the Indian engineering conglomerate. Its role is specifically to assemble the blanket modules — the panels that line the interior wall of the vacuum vessel and act as the first physical barrier between the plasma and the reactor's structural components. These panels of the first wall are directly exposed to the plasma, which means their positioning has to be exact. A misalignment of even a few millimeters could compromise the reactor's performance.
Two of these 36-ton robots are planned to work simultaneously inside the tokamak, alongside a mobile manipulator and a backup manipulator, all developed in coordination with CNIM Systèmes Industriels, the French company providing the main telemanipulator arm and the mobile manipulation system.
The scale of the assembly challenge inside the tokamak
Installing ~20,000 components inside a vacuum vessel is not simply a logistics problem. It is an engineering problem of a different order, where the margin for error approaches zero and every action has to be planned, rehearsed, and executed with mechanical precision.
What goes inside the reactor
The list of components to be installed covers the full spectrum of plasma control technology:
- Vertical stabilization coils for the plasma
- Instability control systems
- Blanket modules (the structural lining of the vacuum vessel)
- First wall panels directly exposed to plasma radiation
Each of these systems plays a role in sustaining the 500 MW fusion plasma that ITER is designed to produce. Some individual components weigh several tonnes, which means even moving them into position requires robotic systems capable of combining raw lifting power with sub-millimeter precision.
Rolling waves: the parallel assembly strategy
To manage the complexity and compress the timeline, the ITER assembly team has adopted what is described as a "rolling waves" strategy. Rather than completing one zone before moving to the next, multiple robotic systems work in parallel across different sections of the tokamak simultaneously. This approach reduces overall assembly time and limits the cascading risk of errors: if one zone encounters a problem, the others continue uninterrupted.
The planned rhythm is demanding by any measure: 24 hours a day, 6 days a week, for approximately 2 years. Human operators will not be absent from this process. They will use mobile platforms with gravity compensation to work alongside the robots in areas where manual intervention is required, but the robotic systems carry the bulk of the mechanical load.
The ITER tokamak is designed to produce a fusion plasma of 500 MW, with a target date for first plasma experiments (deuterium-deuterium) around 2035. The assembly phase currently underway represents one of the most complex precision engineering operations ever attempted.
Recent milestones confirm the precision required
The theoretical tolerances described in the project documentation are not abstract figures. They have already been tested in practice, with results that validate the program's approach.
Four sector modules already in the pit
During 2025, three sector modules — n°7, n°6, and n°5 — were successively installed in the tokamak pit. Each installation served a double function: completing a section of the vacuum vessel and validating the lifting and alignment procedures for the next. On January 29, 2026, the fourth module, n°8, was lowered into position. The operation involved lifting 1,300 tonnes of assembled structure while maintaining a mechanical tolerance of 0.4 mm. That figure is not a typo. A structure weighing more than a thousand tonnes, positioned with a margin smaller than half a millimeter.
This level of precision defines the standard for everything that follows. When the 36-ton blanket assembly robots eventually move inside the vacuum vessel to install the first wall panels and blanket modules, they will be operating in an environment where these tolerances are already established as the baseline expectation.
Industrial spinoffs: from fusion to the automotive sector
The technology developed for ITER does not stay within the reactor's walls. Metromecánica, the Spanish company responsible for developing the automated dimensional metrology system used to verify component positioning inside the tokamak, has already transferred its measurement technology to the automotive industry. The precision measurement tools designed to confirm that a fusion reactor component sits within 0.4 mm of its intended position turn out to have obvious applications in any manufacturing environment where dimensional accuracy matters.
Robotics and metrology technologies developed for ITER’s extreme-precision assembly are already finding commercial applications in automotive manufacturing — a direct industrial benefit from fusion research investment.
This kind of technology transfer is not unusual in large-scale physics projects, but the ITER case is particularly striking because the metrology challenge is so extreme. Measuring positions to sub-millimeter accuracy inside a structure as large and geometrically complex as the ITER tokamak required developing new tools entirely. Those tools, once proven, become commercially viable in sectors where the precision requirements, while still high, are considerably more forgiving than inside a fusion reactor.
The broader robotics ecosystem around ITER reflects the same dynamic. CNIM Systèmes Industriels in France, Larsen & Toubro Ltd. in India, and Metromecánica in Spain each contribute specialized capabilities that did not exist in their current form before this project. The demand for robots capable of working in confined, radiation-exposed environments with force-torque sensing and advanced vision systems pushes the state of the art in industrial automation in ways that eventually filter into other industries.
And while the reactor itself remains years from producing its first plasma, the assembly program already demonstrates something significant: that the engineering challenges of fusion energy, once considered purely theoretical, are now being solved one component at a time, with machines that did not exist a decade ago, working to tolerances that would have seemed impossible outside a laboratory. The 36-ton robot replacing Godzilla is not just a bigger machine. It is the physical expression of how far the program has come — and how much precision the next phase demands.
The horizon for first plasma sits around 2035, with deuterium-deuterium fusion experiments as the initial target. Between now and then, the rolling waves of robotic assembly will continue, shift after shift, inside one of the most complex structures ever built by human hands. Just like the engineering logic behind nuclear-era civil protection demands infrastructure built to withstand extreme conditions, ITER's assembly program demands tools built to operate within them — and the robots being developed for this task represent the current frontier of what industrial machinery can do.
