Ansaldo Nucleare installs over 1,000 welded attachments on ITER Vacuum Vessel
14 January 2021
16th December 2020 marked yet another milestone at ITER, as Ansaldo Nucleare completed the welding activities for the installation of crucial diagnostics, instrumentation and a cable tray on Vacuum Vessel Sector #6 (VVS#6).
As part of the Tokamak Assembly Works at ITER, specialist engineers from Ansaldo Nucleare were required to weld a total of 1,483 attachments onto the VVS#6*. Despite a delayed start to this construction work package, the experience and dedication of the welding team ensured the works were completed almost a month ahead of initial forecasts.
A crucial component of the ITER Tokamak, the Vacuum Vessel is a hermetically sealed steel container that has been designed to house fusion reactions and act as a first safety containment barrier. As the only DYNAMIC shareholder with knowledge and experience on VVS welding preparation and execution, Ansaldo Nucleare was therefore deemed technically best qualified to oversee this critical activity of the Vacuum Vessel’s pre-installation.
The design of the VVS#6 presented two unique challenges. The first was that its curved and complex geometry made it difficult for engineers to access all areas of the vessel, an obstacle that was overcome thanks to the introduction of numerous purpose-designed access platforms from common Access Modular Platforms (COTS) available in the market.
The curved shape of the VVS#6 also meant that traditional methods of marking and laying out welding positions – either by measuring from existing features or using a template – would be ineffective. Considering the sheer quantity of attachments required, it was clear that these inherently time-consuming and error-prone techniques were not appropriate for such a task.
To ensure the accuracy of the welded attachments’ locations, welding experts from Ansaldo Nucleare used a cutting-edge laser templating technique to project temporary markings onto the vessel with a safe, low-power laser. This allowed the welders to precisely align each component according to its projection, without having to burn any permanent marks onto the surface.
Andrea Barbensi, Technical Manager at DYNAMIC snc, explained the benefits of using this technique over a number of potential alternatives: “Although operating the laser templating system is simple, the technology required to accurately project a component position onto a curved surface is complex.
“Only after these precise measurements were identified could we weld the attachments to the vacuum vessel. Considering the total 75 km of in-vessel cabling required, the benefits of using the laser templating system to indicate the complex routing of the cables were obvious.
“Welding each attachment in its precise pre-defined position is an essential prerequisite for the reliability of the diagnostics and instrumentations’ measurements during the Plant operation phase. The laser templating technique we employed ensured these requirements were met with greater accuracy and speed.”
Overall, a total of 150,000 attachments will be required to be welded across all nine sectors of the Vacuum Vessel before it can successfully be installed, each fitted within a few millimetres of tolerance.
The next sector due to undergo these initial welds (VVS#7) is expected to be delivered on site by spring 2021, after which Ansaldo Nucleare will begin a similar work package by summer. The third and fourth Sectors will arrive in late 2021.
The ITER-TAC2 contract is managed by DYNAMIC S.N.C, a special purpose joint company established by ANSALDO as the partnership leader, Endel ENGIE (France), SIMIC (Italy), ORYS (France) and LEADING (Spain).