Machining workshop opens on site
Construction of an on-site machining workshop began in December 2019 and was completed on schedule in September 2020.
TAC2 scope includes complex lifting, positioning, welding and inspection tasks for ITER's toroidal field coils, vacuum vessel sectors, thermal shields and ports. Initial work will take place in the Assembly Hall, before the bulk of the effort is moved to the central Tokamak pit.
Finishing touches on site
The new workshop includes two milling machines (one vertical and one horizontal) and a large CNC (Computer Numeric Control) machine that operates along three dimensions to produce 3D parts. A work area is set aside for welding, with a smoke exhaust and a welding table. A special room is dedicated to metrology, so temperature and humidity can be controlled to avoid skewed measurements. In addition to the shared spaces, the structure includes offices for area managers of the companies in the DYNAMIC consortium.
"We retrofit by taking measurements just before the direct assembly of the components in the Tokamak pit, or in the sector sub-assembly tool in the Assembly Hall. Retrofitting is required, for example, when you try to assemble two components and there is a gap. You need to machine the third piece, called a shim, to fit the exact gap and this is not something you can do before assembly."
Shims will be used for mechanical parts, but they will also be used to make corrections on concrete structures, which are even more prone to misalignment. "Concrete expands and shrinks more than the metal," says Vendeuvre. "And pouring concrete cannot be done within the same final tolerance as you would get with very precise machining operation. The tolerance for placing concrete is +/- 10 mm. But for mechanical parts, and especially for the assembly we need to do in the tokamak, we need much lower tolerances—less than 1 mm sometimes."