The first section for the vacuum vessel (section 6) for the International Thermonuclear Experimental Reactor (Iter) under construction at Cadarache France has been produced in South Korea and is being prepared for shipping, Iter said.
The 5000-tonne vacuum vessel will house the world's first reactor-scale fusion plasma.
Vacuum vessel sector 6 was formed from four poloidal segments, plus upper and lower port stub extensions.
According to Iter's assembly plan, vacuum vessel sector 6 needs to arrive first on site, followed later this year by sector 7 (which is 92.8% complete at Hyundai Heavy Industries). Korea is providing four of Iter's nine vacuum vessel sectors; Europe is providing the other five.
During factory acceptance tests carried out in March and early April, manufacturer Hyundai Heavy Industries and procuring Domestic Agency Iter Korea were able to demonstrate that the 440-tonne vacuum vessel sector 6 met all Iter Organisation's technical specifications.
The Iter vacuum vessel is subject to very specific codes and regulations covering material procurement, design and analysis, fabrication, welding, and examination.
Seven permanent inspectors (five from the Iter Vacuum Vessel Project Team and two representing the French Nuclear Safety Authority (ASN), as well as the Hyundai quality departments, controlled a total of 45,000 inspection points and 500 manufacturing documents.
In December 2019, the French experts travelled to Korea to perform a final in-depth inspection on the near-completed sector.
The Iter vacuum vessel is a heavily welded structure, with steel plate thicknesses of up to 60mm and a large number of permanent attachments. The team developed 60 special scanning techniques using phased array ultrasonic tests (PAUT) to verify gap welds of up to 21mm. The total length of full penetration welds on the sector is nearly 1000 metres, Iter said.
Korean teams began producing the first of four poloidal segments for sector 6 in 2012. Although different in design, each segment required the same fabrication process. First, contractors formed and welded the inner shell. Then they attached inner ribs and support housings, installed in-wall shielding blocks, and in the final step fitted and welded the outer shell.
By September 2019, the four segments for sector 6 were ready to be assembled into the final D-shaped vaccum vessel sector, and upper and lower port stub extensions (procured by Russia and Korea respectively) could be attached through splice plates.
"Through all of these activities, the main point is that we pioneered traceability, recording all activities prior, during and post manufacturing with approved formats of documents," says Chang Ho Choi, who leads the Vacuum Vessel Project Team. "This is important because vacuum vessel procurement involves four Iter Members, and that final assembly will be carried out by Iter Organisation contractors on site. Proper documentation, therefore, will make everyone's job easier."
Chang noted that collaboration was a key part of the project, with 53 monthly meetings over the years and 10 on-site meetings and visits to manufacturing facilities.
"This gives us confidence as we head toward the most important moment of all: machine assembly."
When Iter vacuum vessel sector 6 arrives in France this summer, it will be moved into the Assembly Building and transferred by overhead crane to a laydown area. After a final helium leak test and site acceptance test, the component will be ready for a series of installation activities, Iter said.
Photo: A ceremony was held on 20 April in Ulsan, South Korea, to mark the completion of the first ITER vacuum vessel sector—a remarkable piece of tokamak engineering has been more than 10 years in the making (Credit; Iter Organization)