The ITER Organisation announced that the lower cylinder of the cryostat for the international experimental tokamak nuclear fusion reactor under construction at Cadarache in France has been settled in its final position.

“The gap between the two cryostat sections has been reduced to just 6 millimetres or less and automatic welding operations are ready to start,” ITER noted.

The welding task, which is expected to last 4-5 months, will be carried out by specialists from MAN Energy Solutions—the same Indian Domestic Agency contractor that was in charge of assembling and welding the cryostat segments in the Cryostat Workshop.

The cryostat base, which was inserted into the assembly pit in May, was an exceptionally heavy, uniform and rather rigid component. The ring-shaped lower cylinder, although much taller (12m vs 4m), was a considerably lighter load (375t compared with 1250t). However, due to its diameter, thickness and many large openings it was more "flexible" and likely to deform, ITER said. In addition, its mass was unevenly distributed: on one side, the neutral beam port area added significant weight, which required a specific rigging arrangement.

The cryostat lower cylinder had sat in storage for more than a year, since April 2019, “solidly encased in its steel frame and carefully cocooned in airtight material”. In August, it was lifted, transferred and inserted in place over the course of one week. This involved laser measurements, the installation of complex rigging, the connection to the overhead crane, and finally a test lift to determine the importance and range of deflections, ITER said.

By 31 August, the lower cylinder hovered just above the mouth of the empty Tokamak pit, which has since been equipped with a number of protruding components that reduced already tight clearances to less than 10cm at the narrowest points. “Alignment with the cryostat base and the openings in the bioshield wall meant also that stringent rotational tolerances had to be met,” ITER said. “Watching the huge and almost frail component slowly slide down the pit, each opening in the steel ring aligning with the corresponding opening in the concrete bioshield, was an unforgettable experience. As the lower cylinder settled on temporary hydraulic jacks, just a few centimetres above the base, one felt a sense of awe for the precision engineering that had just been demonstrated.”

Now lower cylinder is settled in its final position.

Video: Installation of the cyrostat lower cylinder by ITER Organization