The transfer of sector module No 7 to the tokamak assembly pit was described as a “record performance” by ITER Detector-General Pietro Barabaschi and a “top-level achievement” by the head of the Construction Project Sergio Orlandi “The present operation brings us back on track for the machine assembly phase,” wrote ITER Machine Assembly Program Manager Jens Reich in an email to the teams.
The module is one of the nine “building blocks” that will, once assembled and welded, form the doughnut-shaped vacuum vessel of the tokamak under construction at the International Thermonuclear Experimental Reactor (ITER) in Cadarache, France. Sector module No 7 is as tall as a five-storey building and as heavy as four fully loaded jumbo jets. It is a complex assembly of first-of-a-kind components procured by three different ITER members: Korea for the vacuum vessel sector at the module’s core as well as the thermal panels that contribute to its insulation, and Europe and Japan for the pair of toroidal field coils that “bookend” each side.
Creating a module from these three major components, as well as all the necessary piping, joining elements and accessories, is a lengthy operation. In 2021 and 2022, the assembly of sector module No 6 required 18 months of work. The module was installed in the tokamak pit in May 2022 but had to be extracted 14 months later for repair. The many lessons learned throughout this initial operation enabled the teams to reduce the assembly time of sector module No 7 to just six months and 10 days.
“The cornerstone of the entire operation is the engineering definition of the task, properly documented and well understood by the executants,” explained Daniel Coelho, the ITER assembly engineer who coordinated the operation three years ago and again for sector module No 7. “Whereas most of the people involved are tasked to apply rules and procedures, we still need a handful of people with a deep understanding of the reasoning behind the rules, in order to properly evaluate deviations to the process that arise and adapt with confidence in case of need.” To reinforce this approach, “veterans” from the sector module No 6 operations in still present on the ITER site but working in other parts of the project, were temporarily re-allocated to the recent operation.
As the module nears the opening of the tokamak pit, the clearance between the floor and the bottom of the load does not exceed 25 centimetres. On the eve of the transfer, the teams rehearsed the very first sequence of the operation. This “pre-lift,” involved lifting the 1,350-tonne load approximately 50 centimetres a prelude to its full extraction from the sector sub-assembly tool (SSAT). The pre-lift allows for the thorough testing of every instrument involved in the full transfer, the practice of the initial sequences, and the coordination of the personnel involved.
For those who had been present during the May 2022 operation, everything seemed to go exceptionally quickly and smoothly. “The overhead cranes have proven to be much more reliable, with nearly no delay when compared to the two hours of immobilisation we had experienced due to technical issues in 2022,” noted Coelho.
After the module began its descent into the 30-metre-deep tokamak pit, the swinging of the load due to the inevitable “pendulum effect” made the last phase of the insertion particularly delicate. This was invisible to the eye, but quite apparent in time-lapse videos. At certain critical points, the clearance between the module and elements inside the tokamak pit did not exceed a few centimetres. “Not a walk in the park…” Coelho commented.
The insertion of the repaired sector module No 6, which is now being reassembled, is scheduled for July.
