The ITER Organization and the Spanish company Equipos Nucleares S.A. (ENSA) signed the contract for the welding of the ITER machine’s nine vacuum vessel sectors and 54 port structures.
In addition to on-site welding and testing operations, the contract - which is worth EUR 74.5 million - includes the development of specialized welding and testing tools. More than 150 people, including highly skilled welding and testing personnel, are expected to be involved in the task to complete the field joint welding and testing on the ITER site over a time-span of four years.
ITER’s vacuum vessel is a torus-shaped, double-walled structure made out of 60-mm-thick, ITER-grade austenitic stainless steel. The vacuum vessel will be manufactured in nine sectors (two by Korea and seven by Europe) and delivered to the ITER site. The nine vacuum vessel sectors will be sub-assembled with thermal shielding and toroidal field magnet coils before being positioned in the machine pit by crane.
Each vacuum vessel sector must be aligned and welded to the other sectors using a Narrow Gap TIG (Tungsten Inert Gas) welding process. Welding will proceed by triplets: three sectors will be welded together to form a triplet; three triplets will then be aligned and welded together quasi-simultaneously.
The nine sectors will be connected via inner and outer splice plates. These will be custom machined to accommodate dimensional differences between the vacuum vessel sectors and to facilitate their relative alignment. The splice plates will also allow access between the sectors prior to welding in order to first connect the joints between the silver-coated thermal shields that surround each vacuum vessel sector. The nominal width of the splice plates is 160mm on the inner shell and 100mm on the outer shell.
In the ITER machine, because the thermal shielding completely restricts access to the outer shell of the vacuum vessel during assembly, it will only be possible to access and weld these joints from one side, whereas normally such welding would be performed from both sides. Access is so difficult that narrow welding torches will have to be developed. Robots will deploy the torches in areas where man-access is not possible.