With its layer of soft soil removed, the ITER Assembly Hall work site looks a lot like the surface of an alien world. Fine white dust and sharp debris cover the ground. Methodically boring holes deep into the substratum, a lone, insect-like drilling rig adds to the illusion. With a bit of red in the sky it would be easy to believe we were walking on Planet Mars …
Located adjacent to the temporarily deserted Tokamak Seismic Pit, the Assembly Hall area is the site of the latest construction campaign on the platform. This 60 metre by 100 metre rectangle of earth will host the 57-metre-high edifice in which ITER components will be assembled prior to their installation in the Tokamak.
As a follow-up to the scrapers, excavators and dump trucks that removed some 10,000 m_SUPERSCRIPT_3_/SUPERSCRIPT_ of soil in three weeks, the drilling rig is carrying out „soil investigation.” Long drill bits are being pushed as deep as 7 metres below the surface in order to identify possible discontinuities or cavities created by water erosion (karsts).
The rig will drill a total of 500 holes, collecting and transmitting data to the Engage/Fusion for Energy/ITER Organization team that manages the project. Geologists will then assess the rock profile and determine what treatment should be applied.
A month from now, workers will begin to pour a layer of blinding concrete over the 6,000 m_SUPERSCRIPT_2_/SUPERSCRIPT_ surface. Foundation work will then begin in earnest.
Although less spectacular than those of the Tokamak Pit (no seismic pads will be installed), the foundations of the Assembly Hall will carry their fair share of challenges. The basemat (2.2 metres thick at the perimeter and 1.2 metres thick in the centre) will have to accommodate openings, or „penetrations,” for electrical galleries, drainage, piping, and tunnels to service the neighbouring Tokamak Complex.
„Due to the challenge of ITER itself, it was necessary to incorporate a lot of flexibility in the design of the penetrations,” says Miguel Curtido, Fusion for Energy’s technical project officer for the Assembly Hall. „Space has to be reserved for them early on, when we begin installing the iron rebars prior to pouring concrete. The same holds for the anchor plates for the assembly tooling, which have to be embedded in the concrete. Their definition can still evolve.”
Coordinating action on the Assembly Hall foundations and on the nearby „TB-alpha” worksite (more galleries and tunnels) that will open two months from now will be another big constraint to work with. „This will be the first time we need to manage the interfaces between different contractors working in such close proximity, which can drastically impact execution methodology."
Progressively, the barren, Mars-like landscape will give way to one of the most spectacular construction projects on the platform—the dramatic antechamber to the Tokamak Building.