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Sector repair has started

25 Mar 2024

Built up against vacuum vessel sector #7, the scaffolding reaches almost 20 metres in height and masks the massive component. Streaks of blinding light, filtered by thick, semi-transparent red plastic sheets, flash here and there—proof that in the ITER Assembly Hall, the repair campaign has begun in earnest.

VVS7-REPAIR_3.jpg
Operating from protruding platforms located at different levels of the scaffolding, four welders have started the long and patient task of metal build-up on the regions of the sector bevel affected by dimensional non-conformities.
On small platforms that extend out from the main structure, four welders are concentrating on their highly meticulous job. Pass after pass, following a strictly predefined pattern, they deposit small beads of melted metal on the faulty sections of the sector joint region, called the bevel. As welding rods are consumed one after the other, the deposits grow and reach the required thickness. In a second stage automated machining tools, some of them already positioned, will remove the excess build-up and restore the bevel's geometry as close as possible to nominal.

For an experienced welder the operation is simple, almost routine. However, it requires extreme concentration to achieve uniformity, homogeneity and reliability. It is also a lengthy operation—it is estimated that sector #7, like sector #6, will require approximately 24 kgs of metal fill-up before machining.

VVS7-REPAIR_1.jpg
The parallel passes of metal build-up are clearly visible on the sector bevel in the upper left part of this image. Once manual build-up is complete, automated machining tools will remove the excess metal and restore the bevel's geometry as close as possible to nominal.
The repair operations that have begun on vacuum vessel sector #7 are the result of close to one year of preparation and strategy refinement. Metal build-up and machining were practiced on "representative coupons"—1.4-metre-long mockups of vacuum vessel bevel sections—and mechanical properties were tested before validating the procedures that are being implemented.

"From the beginning, we have worked and continue to work as an integrated project team," says Alessandro Bonito-Oliva, the head of ITER Tokamak Program. "We are also proceeding in close connection with our European Domestic Agency counterparts who are implementing similar operations on the yet-undelivered vacuum vessel sectors."

See the photo gallery below for more detail about the start of vacuum vessel sector #7 repair.

 

With a precision of 0.05 millimetres, laser metrology has mapped the geometry of every section of the bevel affected by dimensional non-conformities. For each section the data obtained is made available to the welder, both as a printed document and as markings embossed on the component itself.
Some 20 metres above the shop floor, at the top level of scaffolding, two platforms protrude from the main structure to provide workspaces for welders. At regular intervals during the build-up process, quality control specialists come by to inspect the work performed by the welders. Operations on sector #7 are not the only activities in the Assembly Hall: also visible to the right of this image, a team on the ground is preparing to stack a third central solenoid module.
Seen from below: two automatic machining tools are positioned to rectify affected bevel sections at the bottom of the sector. Components for the machining tools are standard but they are assembled here in a way that combines lightness and rigidity.
Machining tools are programmed to follow a precise trajectory along the bevel area. Here, specialists from Metalock Engineering UK, contractor to the SIMANN consortium (SIMIC/Ansaldo Nucleare), are fine-tuning the initial positioning of the tools prior to actual machining.
A welder is building up metal along a section of the bevel region. Reference and guiding documents are visible on the right, taped to the red, semi-transparent plastic curtain thta protects personnel on the outside from the blinding light of the torch's electric arc. Four welders are operating at different levels.
For an experienced welder a build-up operation is simple, almost routine. However, it requires extreme concentration to achieve regularity and homogeneity in the successive deposit of the small beads that form a "pass."
A welder checks the temperature of the pass he completed a moment before. He will not proceed to make another pass before the temperature falls below 116 °C.
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