Aiming for three times as fast
In January 2023, ITER carried out the most delicate handling operation it had ever performed: the removal of vacuum vessel sector module #6, which had been installed in the tokamak pit two years previously. The extraction and subsequent disassembly of this giant component, a modular assembly as tall as a five-storey building and as heavy as three fully loaded jumbo jets, was the consequence of non-conformities identified in two of its sub-components: dimensional deviations on the sector’s interfacing surfaces (the “bevels”) and through-wall cracks in thermal shield cooling pipes which needed to be repaired outside the tokamak pit. The four-day-long “reverse lift,” followed by a painstaking disassembly process that lasted approximately six months, provided ITER with a treasure trove of experience. The abundance of lessons learned will eventually divide by a factor two and a half to three the assembly time required for each of the nine modules of the ITER vacuum vessel.
Assembling sector module #6 was a first-of-a-kind operation involving first-of-a-kind components¹. And so too was the disassembly process once the module had been extracted from the tokamak pit and placed inside one of the sector sub-assembly tools. “We learned a tremendous lot throughout both operations, especially when we began disassembling the module,” says Sergio Orlandi, head of ITER’s Construction Project. “In fact, disassembly is the best method to improve assembly procedures and generate more robust processes.”
The lessons learned extend well beyond the components themselves and are not exclusively technical. “There was a lot to be desired for instance in overhead crane performance—the real bottleneck of sector module assembly,” according to Orlandi. “We invested a lot of money in maintenance, rationalized the tool’s management, replaced faulty sensors and improved the overall performance of the instrumentation and control systems.”
When assembling sector module #6 the first time, days were spent (Orlandi says “wasted”) on the step-by-step approval procedures of technical documents such as the engineering and construction work packages that are transmitted to the contractors. This time, a new consortium (CNPE²) is in charge and a different, more efficient approach has been implemented for present and future assembly operations. “Now the documents are ready at the moment we sign the contract,” says Orlandi. “The work scope is clearly defined and comes with a firm price—that is a major difference. As assembly progresses, we only need the approval of the company that certifies nuclear conformity (called an Agreed Notified Body3 in France). That’s an important change-generating value. We are cutting down on dead time to be more efficient and improve quality.”
Another area where time-saving measures have been implemented is metrology. Metrology is used to verify the as-built configuration of a component as well as the alignment of interfacing elements, data that is then used as input in deciding the reverse engineering of shims that fit into the gaps of two adjacent surfaces. “Metrology was also taking a lot of time: surveys were implemented by different companies under different responsibility levels and the results were not always aligned. Here too we have rationalized the approach so that metrology is now done by the ITER Organization exclusively. We have acquired a much better understanding and command of the global complexity and the input data necessary for engineering applications.”
Not all gains, however, are concrete and quantifiable—“spirit” has also been key to the technical, administrative and organizational improvements that have been achieved. “The teams are determined,” says Orlandi. “They are working three shifts and will not even stop for the Christmas recess. The impact of motivation on work quality is undeniable.”
The head of the Construction Project is convinced that the new methods and procedures, the improved organization, the dependability and performance of the upgraded tools and, above all, collective determination will allow the teams to complete the ongoing assembly of sector module #7 in the first quarter 2025—a seven-and-a-half month process compared to the 18 months spent on the initial assembly of sector module #6. “We aim to do even better for the re-assembly of sector module #6, which we plan to achieve in six months.” Sector module #6 is presently in the last stages of repair, with one side already completed and the other to be finalized in the coming days.
Every module assembly will now have to comply to Orlandí's challenging six-month objective. “We have a rigid and very challenging time schedule,” he concludes, “and the stakes are very high.”
¹A sector module is made up of one vacuum vessel sector and corresponding thermal shield panels, plus two toroidal field coils. Nine 40-degree modules, once assembled and welded together, form the doughnut-shaped plasma chamber.
²The CNPE Consortium (China Nuclear Power Engineering; China Nuclear Industry 23 Construction Company Ltd.; Southwestern Institute of Physics; Institute of Plasma Physics, Chinese Academy of Sciences ASIPP; and Framatome) is responsible for sector module sub-assembly (assembly of the vacuum vessel sectors with toroidal field coils and vacuum vessel thermal shielding). In partnership with SIMIC S.p.A., CNPE is also executing the contract for assembly in pit works for 9 sector modules (aligning and using intercoil structures to connect the sector modules).
³An Agreed Notified Body (ANB) is a company authorized by the French Nuclear Regulator ASN to assess the conformity of components in the pressure equipment category (ESPN).