M Merola

Critical heat flux analysis and R&D for the design of the ITER divertor

The vertical target and dump target of the ITER divertor have to be designed for high heat fluxes (up to 20 MW:m 2 over :10 s). Accommodation of such high heat fluxes gives rise to several issues, including the critical heat flux (CHF) margin which is a key requirement influencing the choice of cooling channel geometry and coolant conditions. An R&D programme was evolved to address the overall CHF issue and to help focus the design. It involved participation of the four ITER home teams and has been very successful in substantially expanding the CHF data base for one-sided heating and in providing more accurate experimental measurements of pressure drop (and derived correlations) for these geometries. This paper describes the major R&D results and the design analysis performed in converging on a choice of reference configuration and parameters which resulted in a CHF margin of : 1.4 or more for all divertor components.

Joining of C/C composites to copper

Abstract High heat flux components in International Thermonuclear Experimental Reactor (ITER) are designed as layered structures. In particular, in the heat sink, the assembling of the different parts foresees several joints between C/C composites and Cu alloy. In this paper, two methods to join silicon doped C/C (CFC NS31) to pure copper are described. One method concerns the use of a commercial brazing alloy (70Ti–15Cu–15Ni). The brazing process was optimised and the shear strength of the joined samples resulted to be comparable to the interlaminar shear strength of the C/C composite. The second technique is based on the casting of copper on C/C. The C/C surface was modified by direct reaction with a transition metal. The obtained modified C/C resulted very well wettable by molten copper. The morphological analysis of the C/C–Cu samples was performed.

Status of fabrication development for plasma facing components in the EU

This paper summarises the European R&D efforts for the manufacture of shield modules and divertor cassettes for the International Thermonuclear Experimental Reactor (ITER), including their plasma facing components. The various development steps are described as they had to be taken to resolve the fabrication issues, and to keep track with the evolving design requirements and solutions. For all components, the manufacturing feasibility has been demonstrated on prototype scale which puts Europe in the position to start the procurement as soon as the decision about ITER construction is taken. The time period remaining until then is used to optimise the fabrication processes and to develop more cost effective alternatives.

Overview of the EU Small Scale Mock-up Tests for ITER High Heat Flux Components

Abstract This task within the EU R&D for ITER was aimed at the development of basic manufacturing solutions for the high heat flux plasma facing components such as the divertor targets, the baffles and limiters. More than 50 representative small-scale mock-ups have been manufactured with beryllium, carbon and tungsten armour using various joining technologies. High heat flux testing of 20 of these mock-ups showed the carbon mono-blocks to be the most robust solution, surviving 2000 cycles at absorbed heat fluxes of up to 24 MW m−2. With flat armour tiles rapid joint failures occurred at 5–16 MW m−2 depending on joining technology and armour material. These test results serve as a basis for the selection of manufacturing options and materials for the prototypes now being ordered.

European development of prototypes for ITER high heat flux components

The extensive EU research and development, on international thermonuclear experimental reactor (ITER) high heat flux (HHF) components aims at the demonstration of prototypes for the divertor and baffle with challenging operating requirements. The recent progress of this development is summarised in the paper, particularly concerning the manufacture and testing of mock-ups and prototypes. The available results demonstrate the feasibility of robust solutions with carbon and tungsten armour.

European Development of the ITER Divertor Target

Abstract The main European contribution to the ITER divertor project was the development of the divertor target with severe operating requirements such as peak heat loads of up to 20 MW/m2. This development involving EU laboratories and industry included R&D on armour materials, thermo-hydraulics testing, component manufacture, high heat flux testing, design and manufacture of prototypes for later testing. The 4-year EU R&D effort achieved the demonstration of the feasibility of a robust divertor target design based on carbon and tungsten armour. This EU solution has eventually been adopted for the ITER reference design and could be valid also for other ITER high heat flux components such as limiters or baffles.

Manufacture and Testing of Small-Scale Moch-ups for the ITER Divertor

This task within the EU R&D for ITER is primarily aimed at the development of solutions for the divertor target which has to be designed for up to 1000 off-normal transients at 20 MW/m2. Representative small scale mock-ups with carbon and tungsten armour have been manufactured using a similar technology. First tests support the analysis which indicates the best high heat flux capability for carbon mono-blocks.

Advanced solutions for beryllium and tungsten plasma-facing components

Abstract Beryllium and tungsten are candidate plasma-facing armour materials for the International Thermonuclear Experimental Reactor (ITER). These armours are proposed for areas with low heat flux (⩽5 MW m −2 ); however, in the divertor, surface melting during abnormal events may occur. This paper reports the progress made in developing novel approaches to solving the difficulties posed in designing with these armours. A Be monoblock brazed to an oxygen free high conductivity (OFHC) 10 mm ID Cu tube using InCuSil `ABA braze alloy has survived 130 cycles of 10–11 MW m −2 for 6 s, with surface temperatures of 1250°C. No visible surface cracking occurred. The same monoblock was then exposed to several cycles of 20–22 MW m −2 for 8 s, creating a 2 mm deep molten layer. High cycle fatigue was then performed. The test results are detailed in this paper. Comparison between experimental and theoretical results are made. W and Cu have a large mismatch in their thermal expansion coefficients and two designs are proposed that minimise the interface stresses. These are: a `brush-like structure with rectangular fibres set in a Cu substrate using the `active metal casting (AMC) technique; and thin monoblocks (or lamellae) brazed or active metal cast onto a Cu tube. Analyses of the lamellae concept for steady-state heat loads of 5 MW m −2 are presented. Fatigue analyses show that both solutions are theoretically viable (∼10 4 cycles). A `brush mock-up has been manufactured and progress on its testing is reported. Results of all tests and their relevance to the ITER design are discussed.

Manufacturing of a full scale baffle prototype for ITER with a CFC and W plasma spray armour

Abstract The European contribution to the development of the ITER baffle will culminate with the fabrication of a full scale prototype with a CFC–plasma spray armour. This paper describes the main features of the prototype as well as the extensive R&D carried out to ensure that the component is fabricated with the required quality.

Design of plasma facing components for the ITER feat divertor

Abstract A comprehensive design of the ITER divertor has been developed within the EU R&D for ITER. It consists of plasma facing components (PFCs) and cassettes body (CB). The PFCs are actively cooled thermal shields while the CB are massive supports for the PFCs providing also a neutronic shield. The present paper gives a detailed design of the PFCs and the CBs. It includes the cooling path, the manifolds, the attachments between the PFCs and the CBs and those between the CBs and the vacuum vessel (VV). The design has been carried out with a series of analyses. The neutronics analysis assures the shielding efficiency of the PFCs/CBs towards the rear components, and calculates the radiation loads in the key points. The electromagnetic (EM) analysis evaluates the loads due to eddy and halo currents. The thermo–hydraulic analysis verifies the effectiveness of the cooling circuit regarding the minimum margin critical heat flux (CHF) and the maximum acceptable pressure drop. The thermo-mechanical analysis verifies the integrity of the components under coolant pressure, neutron/plasma thermal loads and EM loads. The work, done with the collaboration of professionals from different organisations, shows that the proposed design of the components fulfils all the requirements of the ITER FEAT machine.