All of this complexity makes the final assembly stage quite challenging. Activities will be carried out in the following order: TIG welding of the inner shell (full penetration welds), followed by welding of structural ribs (so-called "t-ribs") and flexible support housings, keys, the installation of in-wall shielding, and—in the final activity to complete the segments—TIG welding of the outer shell (full penetration welds). One hundred percent volumetric inspection is required as a nuclear safety requirement.
Taking all assembly activities on sector #6 into account, the Hyundai team estimates the total length of full penetration welds at 1,380 metres.
In order to increase confidence that the stringent tolerance requirements for the final geometry can be achieved, the Hyundai team—in collaboration with the ITER Organization and the Vacuum Vessel Project Team¹—performed a "virtual fitting" this summer in which all available dimensional measurements of the completed poloidal segments were processed with specialized software (Space Analyzer) and matched virtually. "This process was key," explains Chang Ho Choi, who leads the ITER Vessel Division. "It allows the demanding tolerances to be achieved by identifying the areas that require reverse engineering to compensate welding deformation and shrinkage."
From 7 to 15 September, the team completd the inner shell welding on all poloidal segments. Six Project Team inspectors, two Agreed Notified Body² inspectors, and the Hyundai quality departments are performing continuous quality control—day and night—as the work advances. A total of 45,000 inspection points are planned and 500 manufacturing documents, including reports, have been developed.
¹ The Vacuum Vessel Project Team reunites staff from the European, Korean, Indian and Russian Domestic Agencies with staff from the ITER Organization in regular meetings to improve the overall efficiency of vacuum vessel procurement execution.
² An Agreed Notified Body (ANB) is a private company authorized by the French Nuclear Regulator ASN to assess the conformity of components in the pressure equipment category (ESPN).