Design of DTT vacuum vessel and interfaced mechanical systems

DTT is one of the largest superconducting tokamak under construction with the mission to get scientific and technological proofs of power exhaust in prospect of the first nuclear fusion power plant [1,2]. The 5.5MA maximum plasma current, 6T toroidal magnetic field at the plasma center, and 2.19m plasma radius make DTT a flexible and compact facility for testing D-shaped plasmas with different configurations of heat load spreading. The mechanical systems of DTT are designed and integrated analysing interfaces consistently with machine operating states including plasma operation, disruptions, baking, seismic event, testing, and maintenance. Verifications in accordance with design rules apply in particular to the vacuum vessel that is a double-walled structure actively cooled/heated with inter-shell flow. The design of the vacuum vessel is assessed by thermal-hydraulic static and dynamic (LOCA, LOFA, LOVA) analyses, and simulations to assess activated corrosion products. Selection and positioning of machine instrumentation, overpressure protection, manufacturing specifications for fabrication and inspection of welded joints are also evaluated. Finally, UHV gaskets and port bellows compatible with integration sequence and interspace testing, tube bellows and feedthroughs arrangement at the cryostat flanges of the multifunctional ports, three-dimensional inspection on dense point cloud data are defined in parallel to the vessel design. Construction requirements are transferred into technical specifications prepared for vessel call for tender and procurement follow-up. The integrated approach and methodology identifying scope, costs, schedule, and deliverables are transferred into the design and procurement of the systems belonging to the mechanical area that includes machine cryostat, thermal shield, vessel auxiliary systems (vacuum pumping, fuelling and cleaning systems), in-vessel components not maintained with RH (stabilizing plates, in-vessel coils axial symmetric, in-vessel coils not axial symmetric). The paper deals with main technical findings, design review outcomes, and process qualification in the tokamak mechanical area directing efforts towards procurement activities.