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The ITER Tokamak will be the largest device of its kind in the world, with a plasma volume of 840 m³. Photo: US ITER

In the ITER reactor in southern France, the world's largest fusion reactor experiment, the hydrogen isotopes deuterium and tritium fuse at high temperatures to produce superheated plasma. Strong superconducting magnets confine the plasma in a donut-shaped tokamak chamber.

Although ITER is not designed to produce electricity, it paves the way for reactors that can produce electricity. Fusion releases a lot of energy in the form of fast neutrons and charged particles, which heats the plasma. The cladding of the reactor wall traps heat, making it easier to generate steam to power turbines to generate electricity.

Extreme temperatures

Although plasma is ten times hotter than the sun, superconductors require temperatures close to absolute zero to operate.
"This contrast perfectly illustrates the extreme conditions that place special demands on the operation of a fusion power plant. One of the biggest challenges is maintenance, and this is where the Tampere Divertor test platform 2 comes in handy," says Jarmo Alanen, Senior Researcher at VTT.

Future fusion reactors will also feature mega-scale components and fine-tuned, sensitive technology.

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Representatives from F4E, VTT, ITER Organization, Korea and Japan following the Divertor Cassette Remote Handling system demonstration from the control room, DTP2, Finland, January 2024. Photo: VTT

"The good news is that fusion plant elements and nuclear waste will only remain low-level radioactive for about 100-200 years, while fission fuel will remain radioactive for 100 000 years. But of course, during the life of the plant, we will still have to play with highly radioactive particles and elements to keep the plant running," Alanen explains.

The result of years of development

Fusion for Energy, VTT Technical Research Centre of Finland and the University of Tampere have been working together for more than ten years to develop and integrate ITER's remote processing control system into the DTP2 test platform.
VTT hosts the Divertor Test Platform (DTP2), which includes a control room, dedicated remote handling equipment and a full-scale prototype of the ITER Divertor Cassette, weighing about 10 tonnes, 3.5 m long and 2.5 m high. ITER will have 54 such cassettes that will form a divertor, a massive "ashtray" into which most of the plasma impurities will fall. Removing a heavy cartridge requires a robot of the same weight to move through a narrow maintenance tunnel.

The project has been a successful partnership between applied science and industry: VTT developed a virtual 3D environment and a remote diagnostics application, complemented by a GTD Command and Control application, Genrobot robotics software and an LLC communications driver.

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Prototype of the ITER Divertor Cassette, weighing about 10 tonnes, 3.5 m long and 2.5 m high. Photo: VTT

Digital hydraulic valves

The use of digital hydraulic valves for remote operation has also been a game changer in ensuring a more accurate and reliable system operation.

Because fusion reactors are sensitive to contaminants, the remote system uses water-based hydraulics. The digital valve, DigiValve, is an innovation of Tampere University of Technology, Fluiconnecto and Tamlink, which promises increased reliability in demanding environments.

"The servo valves originally used in the remote handling system turned out to be less than ideal, as they wore out easily and were prone to clogging. DigiValves is much more fault- tolerant, as the system with 16 on/off valves is not dependent on just one valve as in the old solution. They are easy to control digitally and offer better performance and very accurate control," says Alanen.

3DNode camera-based monitoring system

Another innovation, the 3DNode camera-based tracking system, measures the coordinates and rotation angles of the cassette from markers placed in the service tunnel and cassette to calculate the robot's pose.

Commercial machine vision solutions exist, but none of them meet the limitations of ITER, such as material properties and the low resolution of radiation hard cameras.

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Lift and tilt movements managed by the digital hydraulic valves in order to ensure better precision and more efficiency when moving the ITER Divertor Cassette prototype. Photo: VTT

Successful demonstration

How would the valves and software work together in full operation? At the beginning of the year, F4E and VTT invited representatives from their subcontractor, the ITER Organisation, and the ITER domestic agencies in Japan and Korea to participate in a demonstration of the system at DTP2 at VTT.

The divertor cassette was carefully transported throughout its journey. The entire remote handling system worked flawlessly without any disruptions.

The cartridge exchange operation was carried out using the ITER compliant remote handling control system implemented by Genrobot and other control system elements mentioned above.

"Although the user can more or less rely on pre-learned motion paths, the operator may need to manually control the robot. Sometimes small movements are needed, especially because of the tight fit of the robot-cartridge interface or to compensate for deflections when lowering a 10-tonne load. The required simultaneous lateral movement and rotation, millimetre by millimetre, without a camera view, is quite a task. The virtual reality model and virtual instruments provided by C&C are crucial," says Alanen.

"DTP2 provides an excellent environment for testing and preparing remote handling systems for ITER's first assembly phase. Work can now begin on new versions of GENROBOT, which aim to simplify and optimise operations," says Emilio Ruiz Morales, F4E's Remote Management Manager, who led the engineering team developing the software.

New commercial opportunities

According to Alanen, these innovations are a good example of applied science and industry working together to create solutions with wider commercial potential. The fusion reactor is probably the most demanding environment in water hydraulics, but the same technology could be used in other industries that need to move large masses with high precision.

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VTT’s Senior Scientist Jarmo Alanen. Photo: VTT

"Construction, manufacturing and transportation are just a few examples of industries that could benefit from solutions developed for ITER's remote handling needs," says Alanen.

"The European-funded work has paid off and can be applied beyond fusion," explains Salvador Esque, F4E's Remote Control Officer, who is responsible for the progress of this device.

"In this technology sector, we have invested in people to acquire new skills and deepen their expertise by developing and validating new technologies. We have funded a test facility that has become a centre of excellence in this field, which can be used for real remote processing operations in ITER. With F4E's participation in this project, we are strengthening European leadership," says Carlo Damiani, Programme Manager for Remote Processing at F4E

Robots for other maintenance tasks

Of course, handling divertor cartridges is not the only task in fusion reactor maintenance. But the conditions are often dangerous and out of reach of humans. Alanen and his team are currently investigating a range of smaller robots that weld, vacuum, tighten bolts and open or close doors inside a radioactive reactor. Many of the tasks are delicate in nature, and excessive use of force can have serious consequences.

"The haptic controller gives the user tactile sensations of what the robot they are controlling is doing. While automation increases efficiency, some tasks still require a human operator. Robotics can be of great help in extending the range of possible activities and increasing the safety of maintenance," says Hannu Saarinen, senior researcher at VTT.

Sources: VTT and F4E