In the context of JT-60Sa Project developed in Naka (Japan), IDESA was awarded with the contract for the fabrication and shop assembly of the Cryostat Base. This structure, weighing around 300 ton and with a diameter of 12 meters, is an assembly comprising seven big stainless steel sectors, that are to be bolted together during final assembly in Japn There are three “lower level” 120º sectors (the Lower Structure sectors), and three “upper level” 120º sectors (the Double Ring sectors) resting on the Lower Structure Sectors. The seventh piece is the Cylindrical Shell, located inside the DR sectors, and resting onto the LS sectors. This solution was adopted in view of the dimensional restrictions to the final land transport between Hitachi Port and final destination at Naka site. The thicknesses of the structure are mostly betwwen 80 and 100 mm. Most of welds are butt or corner welds, full penetration type, so a great amount of weldment is involved. Thus, the control of the distorsion produced during welind activities was essential to fabricate a welded structure that at a later stage can be machined within the required tolerances.

Several ITER components, referred to as in-vessel Components, are located inside the ITER Vacuum Vessel; they will be subjected to special operating and enviromental conditions (neutron radiation, high heat fluxes, electromagnetic forces, etc.). The effects of irradiation on them, including embrittlement, swelling and creep, were not addressed in the existing commercial codes. These conditions are different from conditions in fission reactors and create challenging issues related to the design of these components. The tasks covered were: (a) Modification of design rules, incorporating rules from recently developed codes, and development of specific design rules to cover ITER specific issues and operational conditions, (b) Demonstration of consistency between design rules in SDC-IC and european standards used for manufacturing, in particular EN 13445; identifying areas where consistency is not provided, (c) Assessment of the compliance with the Essential Safety Requirements of the French Regulations (ESP and ESPN).