G. Sannazzaro

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.

Structural load specification for ITER tokamak components

The substantial mechanical loads which can develop in multiple components are a major technical challenge associated with the design of the ITER tokamak. The various loads acting on ITER can be grouped into several types: inertial loads, associated with gravity and seismic events; pressure loads, particularly significant for the ITER pressure equipment; electromagnetic loads, which affect all conducting structures as a consequence of transient events inducing rapid magnetic field changes and which possibly involve currents flowing between the plasma and in-vessel components; thermal loads, which are extremely severe in the plasma facing components; assembly loads, typically due to preloads imposed during assembly.

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.

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.

Dynamic response of the ITER vacuum vessel to electromagnetic loads during VDEs

During vertical displacement events (VDEs) plasma halo currents can flow partly through the passive structure. Additionally induced currents occur in the passive structure. Due to these electrical currents, major electromagnetic forces act on the passive structures and hence on the vacuum vessel (VV). As these forces change in time the vessel response is dynamic. This response determines important design drivers such as the reaction forces at the vessel supports, the vessel displacements and stress levels in the vessel structure, and it affects all components attached to the vessel. It is expected that the most severe dynamic response of the vessel occurs during asymmetric VDEs with slow current quench. Experiments on existing tokamak machines have shown that asymmetric loads can rotate around the vertical machine axis. This possible rotation is considered here. Using the finite element (FE) method the dynamic response of the vessel was analyzed in full transient dynamic analyses for the worst case VDEs according to the ITER VV load specification [2]. A 360° FE model of the VV is used since the loads are partly asymmetric. One major difficulty in this assessment was to predict how the sideways load is shared between three simultaneously acting support types. Attention was therefore given to the modeling of the VV supports including the coupling effect with the toroidal magnetic field.

Seismic analysis of ITER tokamak including interaction with soil and building

Abstract A coupled spectrum seismic analysis of the ITER ‘tokamak-building-basemat-soil’ system has been performed. Soil–structure interaction (SSI) is modelled as a set of springs and dampers. A new method is proposed to replace the detailed finite-element model of the building by an equivalent set of parallel oscillators having the same natural frequencies, modal effective masses and height as the building and creating the same shearing force and overturning moment. The response of the ITER tokamak is found versus different soil parameters. For some particular soil conditions, the natural frequency of the building is very close to that of the tokamak and critical resonance effects may take place.