Yu. Utin

ITER vacuum vessel design and construction

Abstract According to recent design review results, the original reference vacuum vessel (VV) design was selected with a number of modifications including 3D shaping of the outboard inner shell. The VV load conditions were updated based on reviews of the plasma disruption and vertical displacement event (VDE) database. The lower port gussets have been reinforced based on structural analysis results, including non-linear buckling. Design of in-vessel coils for the mitigation of edge localized modes (ELM) and plasma vertical stabilization (VS) has progressed. Design of the in-wall-shielding (IWS) has progressed in details. The detailed layout of ferritic steel plates and borated steel plates is optimized based on the toroidal field ripple analysis. The procurement arrangements (PAs) for the VV including ports and IWS have been prepared or signed. Final design reviews were carried out to check readiness for the PA signature. The procedure for licensing the ITER VV according to the French Order on Nuclear Pressure Equipment (ESPN) has started and conformity assessment is being performed by an Agreed Notified Body (ANB). A VV design description document, VV load specification document, hazard and stress analysis reports and particular material appraisal were submitted according to the guideline and RCC-MR requirements.

Design and thermal/hydraulic characteristics of the ITER-FEAT vacuum vessel

Abstract Recent progress in structural design and thermal and hydraulic assessment of the vacuum vessel (VV) for ITER-FEAT is presented. Because of the direct attachment of the blanket modules to the VV, the module support structures are recessed into the double-wall VV, partially replacing the stiffening ribs between the VV shells to simplify the VV structure. Structural integrity of the VV is provided by the ribs and the module support structures with local reinforcement ribs. The detailed structural design of the VV taking account of the fabricability and code/standard acceptance is presented. Cost reduction of the VV fabrication using casting or forging is proposed. A high heat removal capability is required for the VV cooling to keep the thermal stress below the allowable. It is expected that natural thermo-gravitational convection due to the heat flux from the vessel wall to the water will enhance heat transfer characteristics even in the low flow velocity region.

Design and Development of the ITER Vacuum Vessel

Abstract In ITER, the vacuum vessel (VV) is designed to be a water cooled, double-walled toroidal structure made of 316LN stainless steel with a D-shaped cross section approximately 9 m wide and 15 m high. The design work which began at the beginning of the ITER-EDA is nearing completion by resolving the technical issues. In parallel with the design activities, the R&D program, Full-scale VV Sector Model Project, was initiated in 1995 to resolve the design and fabrication issues. The full-scale sector model corresponds to an 18° sector (9° sub-sector×2) and is being fabricated on schedule. To date, 60% of the fabrication had been completed. The fabrication of full-scale model including sector-to-sector connection will be completed by the end of 1997 and performance tests are scheduled until the end of ITER-EDA. This paper describes the latest status of the ITER VV design and the Full-scale Sector Model Project.

FW/Blanket and vacuum vessel for RTO/RC ITER

Abstract The design has progressed on the vacuum vessel and First Wall (FW)/blanket for the Reduced Technical Objective/Reduced Cost (RTO/RC) ITER. The basic functions and structures are the same as for the 1998 ITER design. The design has been improved to achieve, along with the size reduction, ∼50% target reduction of the fabrication cost. The number of blanket modules has been minimized according to smaller dimensions of the machine and a higher payload capacity of the blanket Remote Handling tool. A concept without the back plate has been designed and assessed. The blanket module concept with flat separable FW panels has been developed to reduce the fabrication cost and future radioactive waste.

Vacuum vessel port structures for ITER-FEAT

The equatorial and the upper port structures are the most loaded among those of the ITER-FEAT vacuum vessel (VV). For all of these ports, the VV closure plate and the in-port components are integrated into the port plug. The plugs/port structures are affected by plasma events and must withstand high mechanical loads. Based on typical port plugs, this paper presents the conceptual design of the port structures (with emphasis on the supporting system), and the results of analyses performed.

Design and Fabrication Methods of FW/ Blanket and Vessel for ITER-FEAT

Design has progressed on the vacuum vessel and FW/blanket for ITER-FEAT. The basic functions and structures are the same as for the 1998 ITER design. Detailed blanket module designs of the radially cooled shield block with flat separable FW panels have been developed. The ITER blanket R&D program covers different materials and fabrication methods in order make a final selection based on the results. Separate manifolds have been designed and analysed for the blanket cooling. The vessel design with flexible support housings has been improved to minimise the number of continuous poloidal ribs. Most of the R&D performed so far during EDA are still applicable.

Design and fabrication methods of FW/blanket, divertor and vacuum vessel for ITER

Abstract Design has progressed on the vacuum vessel, FW/blanket and Divertor for the Reduced Technical Objective/Reduced Cost (RTO/RC) ITER. The basic functions and structures are the same as for the 1998 ITER design [K. Ioki et al., J. Nucl. Mater. 258–263 (1998) 74]. Design and fabrication methods of the components have been improved to achieve ∼50% reduction of the construction cost. Detailed blanket module designs with flat separable FW panels have been developed to reduce the fabrication cost and the future radioactive waste. Most of the R&D performed so far during the Engineering Design Activities (EDAs) are still applicable. Further cost reduction methods are also being investigated and additional R&D is being performed.

In-service inspection and instrumentation for ITER vacuum vessel

In-service inspection (ISI) is required according to the French Order for Nuclear Pressure Equipment and also to protect plant investment and to ensure machine availability. The ITER VV maintenance and monitoring program includes Inservice Monitoring, Periodic Test and Periodic Inspection. Inservice Monitoring includes commissioning tests, continuous vacuum and water leakage monitoring and load follow-on monitoring. Periodic Test includes regular pressure tests and leak tests. For the outer shell welds of the main vessel, the equatorial region of “port #7” and lower penetrations are selected for Periodic Inspection. R&D for ISI is underway and tools and maintenance systems are being developed. Mock-ups were constructed to demonstrate its feasibility. In addition, a study of acoustic emission monitoring has started using a mock-up. The VV instrumentation is a system to monitor the VV status in normal and off-normal conditions. The VV instrumentation system includes approximately 1600 sensors, mounting devices, cables, cable holders, vacuum feed-throughs for the vessel and the cryostat, control cubicles and interrogating systems. Approximately 850 thermocouples are installed to monitor temperatures on plasma-side and cryostat-side surfaces of the vessel. Resistive and FBG strain gauges are also mounted on the vessel surfaces. Displacement sensors and accelerometers are installed to obtain data of VV movements during plasma disruptions or VDEs. These data are utilized to calculate forces on the VV. This calculation is essential to categorize plasma disruption or VDE events during the ITER operational phase.

Critical Issues of the Structural Integrity of the ITER-FEAT Vacuum Vessel

In the ITER-FEAT, the most severe loading conditions for the VV are the toroidal field coil fast discharge (TFCFD) and its load combination with electromagnetic loads due to a plasma vertical instability, which cause high compressive stresses in the VV inboard wall and increase the risk of buckling. Detailed analyses need to be performed to assess the stress level at the geometrical discontinuities and where concentrated loads are applied. The nuclear heating and the presence of gaps between the blanket modules cause concentrated nuclear heat loads. This paper describes the major structural issues of the ITER vacuum vessel (VV), and summarises the preliminary results of structural analyses.

Cryogenic Conduction Cooling Test of Removable Panel Mock-Up for ITER Cryostat Thermal Shield

Abstract This paper describes the fabrication of removable panel for ITER cryostat thermal shield (CTS) and its conduction cooling test at cryogenic temperature. Two kinds of full-scale mock-ups of the removable panels have been developed, depending on different thermal conduction designs. Passive cooling characteristics of the mock-ups are investigated with the measured data of temperature jump at the joint and maximum temperature at the panel. The passive cooling of panel with copper insertion satisfies the design requirement of temperature jump (< 3 K), even though the heat load condition in the cooling test is more severe than the design condition of CTS. It is clearly demonstrated that the copper strips bonded on the panel attenuate the temperature gradient of the panel. Different thermal behaviors at the joint are also found for the two mock-ups.