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.