High heat flux tests in support of the 3-D computational modeling of melting for the EU-DEMO first wall limiters

The EU-DEMOnstration fusion power plant (DEMO) first wall protection strategy relies on limiter components to face both normal and off-normal plasma transient events. The heat loads during these events are likely to damage the breeding blanket’s first wall otherwise. Since W is the preferred plasma-facing material for EU-DEMO, the plasma-facing component design of the limiters follows considerations based on heat transfer in solids undergoing phase transition. The understanding of this problem has paved the way for a 1-D thermal modeling in MATLAB Thermal Analysis foR Tracking InterFaces under meLting&vaporizaTion-induced plasma Transient Events (TARTIFL&TTE), which has then been improved and extended to 3-D geometries within a Multiphysics environment. Hence, the 3-D TARTIFL&TTE implementation in COMSOL Multiphysics. Although the validation has already started against some data available in the literature and described in the companion paper, dedicated experiments are performed in the Garching LArge DIvertor Sample Test Facility (GLADIS) for melting studies. Carried out as a joint activity between EUROfusion and U.K. Atomic Energy Authority (UKAEA), the aim of these experiments is generating a traceable and controlled experimental database in support of heat transfer studies in solid components undergoing phase transition. The data are here used in support of the 3-D TARTIFL&TTE validation benchmark. To broaden the database, three different materials are chosen, i.e., TZM, W, and SS-316 grade. The requirements defining the experiments comply with the hypotheses behind 3-D TARTIFL&TTE, for it to be able to reproduce the experiments. Therefore, a uniform heat flux on the loaded surface is provided by the H neutral beam on the footprint, and loading time and heat flux magnitude are chosen such that only melting is reached. This allows the liquid metal to stay in place once formed. No attempts to reach vaporization are made, since the vertical position of the target promotes the molten layer sliding under gravity effects. Measured and modeled results (temperature, absorbed energy, and melt layer depth) show good agreement during the melting phase. As a stepwise benchmark, validation will be also sought under vaporization events. Future work is focused on addressing this last point

Fabrication and testing of W7-X pre-series target elements

International audienceThe assembly of the highly-loaded target plates of the WENDELSTEIN 7-X (W7-X) divertor requires the fabrication of 890 target elements (TEs). The plasma facing material is made of CFC NB31 flat tiles bonded to a CuCrZr copper alloy water-cooled heat sink. The elements are designed to remove a stationary heat flux and power up to 10 MW m -2 and 100 kW, respectively. Before launching the serial fabrication, pre-series activities aimed at qualifying the design, the manufacturing route and the non-destructive examinations (NDEs). High heat flux (HHF) tests performed on full-scale pre-series TEs resulted in an improvement of the design of the bond between tiles and heat sink to reduce the stresses during operation. The consequence is the fabrication of additional pre-series TEs to be tested in the HHF facility GLADIS. NDEs of this bond based on thermography methods are developed to define the acceptance criteria suitable for serial fabrication

Acceptance tests of the industrial series manufacturing of WEST ITER-like tungsten actively cooled divertor

International audienceThe activelly cooled plasma facing units (PFUs) constituting the WEST lower divertor must meet stricttechnical specifications before their installation into the WEST tokamak. The tests performed at CEAlead mainly: to provide information on the feasibility to attach mechanically PFUs on sectors, toensure geometrical tolerances for the welding of PFUs to water manifolds, to check the PFU vacuumtightness and to confirm the PFUs heat exhaust capability. Using high heat flux (HHF) test facilities,such as HADES at CEA-Cadarache and GLADIS at IPP-Garching,∼5%of the PFU production wastested. Infrared thermography (IR) tests were also performed (∼24% of the PFU production tested).Weshow that PFUs are with a quality in agreement to the requirements and that the assessement of theheat exhaust capability during the series production is needed. Based on statistical approaches, thiswork also provides information on the methods to assess the quality of tested components usingstatistic process control

Manufacturing, high heat flux testing and post mortem analyses of a W-PIM mock-up

In the framework of the European material development programme for fusion power plants beyond the international thermonuclear experimental reactor (ITER), tungsten (W) is an attractive candidate as plasma facing material for future fusion reactors. The selection of tungsten is owing to its physical properties such as the high melting point of 3420 °C, the high strength and thermal conductivity, the low thermal expansion and low erosion rate. Disadvantages are the low ductility and fracture toughness at room temperature, low oxidation resistance, and the manufacturing by mechanical machining such as milling and turning, because it is extremely cost and time intensive. Powder Injection Molding (PIM) as near-net-shape technology allows the mass production of complex parts, the direct joining of different materials and the development and manufacturing of composite and prototype materials presenting an interesting alternative process route to conventional manufacturing technologies. With its high precision, the PIM process offers the advantage of reduced costs compared to conventional machining. Isotropic materials, good thermal shock resistance, and high shape complexity are typical properties of PIM tungsten. This contribution describes the fabrication of tungsten monoblocks, in particular for applications in divertor components, via PIM. The assembly to a component (mock-up) was done by Hot Radial Pressing (HRP). Furthermore, this component was characterized by High Heat Flux (HHF) tests at GLADIS and at JUDITH 2, and achieved 1300 cycles @ 20 MW/m². Post mortem analyses were performed quantifying and qualifying the occurring damage by metallographic and microscopical means. The crystallographic texture was analysed by EBSD measurements. No change in microstructure during testing was observed