Kompaflex AG


Unique Swiss bellows engineering design approved for ITER fusion reactor project

Kompaflex AG has designed, built and successfully tested a large prototype bellows for the ITER tokamak fusion project in Cadarache, France. The bellows will be used to isolate the ultra-high vacuum inside the cryostat from the building environment, whilst withstanding the extreme operating conditions of the fusion reactor. After meeting the challenging requirements of the ITER specification, a further 85 bellows will be manufactured, some as large as four meters in size.

ITER will be the world's largest experimental fusion facility and is designed to demonstrate the scientific and technological feasibility of fusion power for energy purposes.

The huge ITER cryostat is around seven floors high and provides the high vacuum, ultra-cool environment for the ITER vacuum vessel and the superconducting magnets at the centre of the fusion reactor. The cryostat has over 200 access ports—some as large as four metres in size—that provide through-routes for cooling systems, magnet feeders, heating, diagnostics, and the exchange of components.

Eighty-five rectangular bellows will be used between the ITER vacuum vessel, the cryostat and the walls of the ITER building to isolate the ultra-high vacuum inside the cryostat from the building environment, and to allow for thermal contraction and expansion in the structures during operation or movement during seismic events.

Kompaflex AG specialises in the design and production of metallic bellows and expansion joints for high energy physics or fusion research facilities, in their cryogenics and ultra high vacuum applications. The unique manufacturing process means that there is only one welding seam and this is located far away from areas of high mechanical stress.

Kompaflex was commissioned by ITER to design, build and test a full scale prototype bellows that could withstand the extreme operating conditions of the tokamak fusion reactor.

The prototype large rectangular bellows measures 3.6 x 3.2 metres and is made of multiple thin layers of Inconel 625 alloy which can absorb dynamically the thermic expansion movements between the different structures and withstand the full vacuum.

The ITER bellows prototype was tested for helium leakage tightness, squirm, burst pressure test and spring rates. All results confirmed the parameters calculated during the design phase and required by the ITER specification.

About Kompaflex AG

Kompaflex AG is a Swiss company founded in 1981, specialising in the design and production of tailor made expansion joints / bellows for various industries, such as Oil & Gas, Power, Steel industry, as well as high energy physics installations having cryogenics and ultra-high vacuum applications. Kompaflex is proud to be the leading company finding expansion joint solutions for the most challenging conditions such as high pressure, high temperature, corrosive media in all sizes and shapes. Kompaflex employs over 100 people across engineering, product development and manu-facturing at its two sites in Switzerland and the Czech Republic.


Reto Löhrer
Kompaflex AG
Steinebrunn, Switzerland
This email address is being protected from spambots. You need JavaScript enabled to view it.

Schweizerische Eidgenossenschaft
Confédération suisse
Confederazione Svizzera
Confederazium Svizra
Swiss Confederation


Federal Department of Ecomic Affairs,
Education and Research EAER
State Secretariat for Education,
Research and Innovation SERI
Uni Ge
swissmem logo
The Swiss Industry Liaison Office (ILO) is financed by the State Secretariat for Education Research and Innovation SERI. The Swiss ILO Convention signatory members supporting the ILO activity are EPFL, PSI, University of Geneva and SwissMEM.