Extreme Conditions Pneumatic Solutions for Iter Fusion Reactor

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No standard was robust enough for the cryopump systems in the Iter fusion reactor. In cooperation with RI Research and Iter, Konstandin has developed a control cabinet for this purpose. A valve control system with a tolerance of less than one millimeter of play ensures maximum accuracy.

The world's largest fusion reactor is being built in the south of France as part of the international Iter research project. The aim is to generate clean energy by fusing hydrogen nuclei to produce electricity with zero emissions in the long term. 35 nations are involved in the project. The vacuum required for nuclear fusion, the pressure of which is almost equivalent to the emptiness of space, cannot be generated using mechanical pumps alone. Therefore, several cryopump systems with special control technology are also used. However, conventional control systems could not withstand the extreme conditions of the Tokamak reactor. The solution was developed by the company Konstandin from Karlsbad-Ittersbach (Germany), which had already supplied eight large pneumatic cylinders for the cryogenic pumps. In cooperation with RI Research Instruments GmbH and the Iter organization, a globally unique pump control cabinet was created, which precisely controls the large inlet valves with a diameter of almost 39 in with a valve clearance of less than 0.04 in and meets the high requirements for resistance to magnetic fields, radiation, heat and vibration.

"There are no standard solutions at Iter, every component has to be developed in-house," explains Mathias Kraft, Head of Design and Technology at Konstandin. This sentence sums up the requirements for the new project in a nutshell. For the control of the cryogenic pumps, a design was required that not only works reliably, but also functions under environmental conditions that are unique in the world. Iter stands for International Thermonuclear Experimental Reactor and is regarded as the most ambitious energy project of our time. In the future, the tokamak reactor will generate temperatures that are higher than those inside the sun. A highly efficient vacuum system is essential to keep these temperatures under control. Six cryogenic pumps are used to extract the gases produced during the fusion process. However, no suitable control system was available for these pumps. Operation requires precise control of the inlet valve, which is almost a meter in diameter and can only move by fractions of a millimeter (0.04 in) in order to precisely regulate the flow of gases. Konstandin had already supplied RI Research Instruments GmbH with eight large pneumatic cylinders for the cryogenic pumps in 2021. Building on these many years of positive experience, RI Research Instruments GmbH commissioned the company to develop the complete control cabinet at the end of 2023. The requirements came directly from Iter and posed a real challenge due to the safety standards for nuclear applications. The cabinet had to be mounted in port cells directly on the reactor, where it had to withstand magnetic fields, high temperatures of up to sixty degrees, vibrations and ionizing radiation. The cells act as an interface between the reactor core and the outside world. In close cooperation between RI Research Instruments GmbH, Iter and Konstandin, a control system was developed which implements the valve movement pneumatically and therefore particularly safely. The control system enables the required rapid opening and closing of the valve and guarantees positioning accuracy with a margin of less than one millimeter (<0.04 in).

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Pneumatic Control Cabinet Ensures Fail-safe, Precise Control

The control cabinet works as a pneumatic control unit and requires virtually no electronic components, which means that it functions reliably and failsafe even in an environment with strong radiation. It is controlled by an externally positioned PLC-based control unit outside the radiation zone. Pipes feed the control air to larger valves, which drive the piston of the inlet valve and displace 21 gallons of compressed air in just a few seconds. The system enables fast opening and closing, precise intermediate positions and emergency stops. Different speeds can be achieved using special valve circuits, while leak compensation automatically compensates for pressure losses. The double safety valves ensure safe relief in the event of overpressure and even the smallest pressure differences are detected and compensated for. The system is fully piped for long-term safety. Hose connections that would not be permitted in this environment have been avoided. Stainless steel pipes withstand vibrations and temperature fluctuations and guarantee complete tightness. With the compact housing size of 24 × 24 in, the arrangement had to be planned precisely so that every screw connection remains functional and every line accessible. Strict material specifications prohibited fluorine-containing substances and standard seals; special materials for valves, sensors and screw fittings were tested, approved or specially manufactured. Konstandin coordinated the entire process closely with the suppliers and documented every detail in a qualified manner.

Control Cabinet: All Test Requirements Successfully Mastered in the Iter Test Facility

"The Iter project placed extraordinary demands on us that went far beyond traditional plant construction. All steps, components and connections had to be tested, documented and approved. Particular emphasis was placed on vibration resistance, temperature resistance, seismic stability and electromagnetic immunity," explains Kraft. Magnetic fields of up to half a Tesla can occur in the port cells, which severely restricted the choice of materials. Installation in the cramped port cells was challenging. In several development loops, the team optimized the cabinet design so that all components could be accommodated and at the same time were robust, easy to maintain and functionally reliable. Availability problems with individual components required the selection and testing of alternative components that met the same safety and material standards. Another focus was the fluorine-free nature of the materials, as conventional seals and hoses could become unstable when exposed to radiation. Special metal seals ensure a reliable seal. During the development phase, new component variants were flexibly integrated, allowing the control system to be further optimized. The real conditions of the tokamak were simulated in the cryogenic test facility and the control cabinet was tested. It worked precisely, reacted stably to pressure changes and passed all load tests without leaks or malfunctions. The specifications for the construction and testing of the control cabinet prototype were developed by Mr. Colbalt Atlantis, design engineer at Iter. The reliability and robustness of the system was fully confirmed. "The operation of the inlet valves was precise, the safety systems responded as planned and the control system is now considered qualified," says Guim Pallas, ACS (Actuator Control System) Responsible at Fusion for Energy, the European agency for the Iter project. This result can therefore also be seen as proof of the ability of German engineering to develop perfect solutions even under extreme conditions.

Control Cabinet Ensures Precise Cryogenic Pump Control And Stable Operation in the Iter-Tokamak

The delivery of the control cabinets in 2025 marks another milestone in the construction of the Iter reactor. The tested systems are ready for integration into the tokamak reactor, which should be completed by 2029. A key factor in the success of the project was the cooperation between the project partners. Konstandin, RI Research Instruments GmbH, Fusion for Energy and Iter have jointly created a system that sets standards worldwide. For the operators, the control cabinet means above all safety and reliability. The cryogenic pumps are precisely controlled, every movement of the inlet valve can be precisely monitored and pressure differences immediately compensated for. The experience gained from the Iter project is already being incorporated into new developments. "We have already received other orders for the development of special cylinders from Iter within the project. In future, other customers from sectors such as energy technology and aerospace will also benefit from the expertise gained here when developing new applications," says Kraft.

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