Strong base for a very heavy task
The first part of the in-pit assembly tool has been installed in the Tokamak pit. When complete, the tool will stand more than 20 metres high and branch out in nine directions to support the sectors of the vacuum chamber as they are welded together.
The same week that vacuum vessel sector #6 was "upended" to vertical in the ITER Assembly Hall, the bottom cylinder of the principal in-pit assembly tool was lowered and anchored onto the basemat of the Tokamak pit.
The two operations are related. The vertical sector will now be transported a few metres and installed on one of the V-shaped assembly tools, where it will be "sub-assembled" with two vertical coils and panels of thermal shielding. The resulting "vacuum vessel sub-assembly," weighing 1,200 tonnes, will then be moved into the pit, where the in-pit column tool will be waiting, ready to support, align, and stabilize the vacuum vessel sub-assemblies as they are joined and welded.
The bottom cylinder is the foundation for the in-pit tool, one of five sections that will form its trunk. Like the other parts of the central column, the 70-tonne component is hollow and "reinforced," designed to support all nine sectors of the ITER vacuum vessel during the assembly phase ... including in the case of a seismic event. Large shear keys, bolted and pinned to the concrete basemat at the centre of the assembly pit under the tool, provide resistance against lateral loads and sliding forces. Inside of the column, "cat ladders" provide access to various levels of the central column, with traps to exit to staging inside of the vacuum vessel.
Each vacuum vessel sector will be supported by a radial beam that shares its load between the central column on one side and the concrete bioshield on the other through brackets embedded in the bioshield wall.
On Saturday 27 March, the assembly contractors lifted the 5.6-metre-tall component and transported it into the pit. The last few metres were the most delicate, as the bottom cylinder was carefully inserted into the round opening at the bottom of the cryostat base, avoiding the edges. Metrology confirmed that the structure was positioned within 2 millimetres of its nominal position inside of the Tokamak Global Coordinate System (TGCS).
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