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This paper presents the enhancements related to the structural analyses of DEMO Divertor in the framework of the EUROfusion Power Plant Physics & Technology (PPPT) program. This activity started two years ago and its preliminary results were published in previous papers. It has been divided in some areas defined by the similarity of the matters they contain: the structural analysis, of utmost importance, has been preceded by a preliminary phase, like the geometry definition or the thermal and the electric-magnetic analysis for loads evaluation; then the structural analysis has been finally confirmed with further evaluations related to excessive deformation or plastic instability. This paper discusses the improvements adopted either in the preliminary analysis or in the main structural analysis. Specifically it highlights the introduction of the thermal and electro-magnetic loads application in terms of a detailed spatial distribution that is now available. More the supports have been introduced in the model and their structural behavior has been investigated considering their interaction with the cassette. The structural assessment, according to the Design and Construction Rules for Mechanical Components of Nuclear Installation (RCC-MRx), has been performed either for the cassette or for the attachments: for the former it is positive while for the latter case serious limitations have been found.

This paper refers to the activity of structural design of DEMO Divertor in the framework of the EUROfusion Consortium. The structural analysis and its preparatory assessments were carried on since a year and the first results were published in a previous paper. The Cassette Body has been examined considering the most conservatives loads (e.g. coolant pressure, volumetric nuclear heating and electro-magnetic loads) according to their latest estimates. This work is based on the design-by-analysis approach adopted in the conceptual design phase of the DEMO Divertor. This design activity has been focused on some key parameters e.g. loads, main geometric dimensions, positions of the Cassette attachments on the vacuum vessel, way of loads application to characterize the structural behavior of the Divertor Cassette. In addition to the existing 3D solid element model, a shell element model has also been developed: with this new model a parametric analysis can be done for a fast optimization. The structural assessment was done according to the Design and Construction Rules for Mechanical Components of Nuclear Installation (RCC-MRx).

Since 2014 preconceptual design activities for European DEMO divertor have been conducted as an integrated, interdisciplinary R&D effort in the framework of EUROfusion Consortium. Consisting of two subproject areas, ‘Cassette’ and ‘Target’, this divertor project has the objective to deliver a holistic preconceptual design concept together with the key technological solutions to materialize the design. In this paper, a brief overview on the recent results from the subproject ‘Cassette’ is presented. In this subproject, the overall cassette system is engineered based on the load analysis and specification. The preliminary studies covered multi-physical analyses of neutronic, thermal, hydraulic, electromagnetic and structural loads. In this paper, focus is put on the neutronics, thermohydraulics and electromagnetic analysis.

An advanced numerical procedure based on imaging of the material microstructure (Image- Based Finite Element Method or Image-Based FEM ) was extended and applied to model the thermomechanical behaviour of novel materials for fusion applications. Two tungsten based heterogeneous materials with different random morphologies have been chosen as challeng- ing case studies: 1) a two-phase mixed ductile-brittle W/CuCr1Zr composite and 2) vacuum plasma-sprayed tungsten (VPS-W 75 vol.%), a porous coating system with complex dual-scale microstructure. Both materials are designed for the future fusion reactor DEMO: W/CuCr1Zr as main constituent of a layered functionally graded joint between plasma-facing armor and heat sink whereas VPS-W for covering the first wall of the reactor vessel in direct contact with the plasma. The primary focus of this work was to investigate the mesoscopic material behaviour and the linkage to the macroscopic response in modeling failure and heat-transfer. Particular care was taken in validating and integrating simulation findings with experimental inputs. The solution of the local thermomechanical behaviour directly on the real material microstructure enabled meaningful insights into the complex failure mechanism of both materials. For W/CuCr1Zr full macroscopic stress-strain curves including the softening and failure part could be simulated and compared with experimental ones at different temperatures, finding an overall good agreement. The comparison of simulated and experimental macroscopic behaviour of plastic deformation and rupture also showed the possibility to indirectly estimate micro- and mesoscale material parameters. Both heat conduction and elastic behaviour of VPS-W have been extensively investigated. New capabilities of the Image-Based FEM could be shown: decomposition of the heat transfer reduction as due to the individual morphological phases and back-fitting of the reduced stiffness at interlamellar boundaries. The microstructure of VPS-W was included in planar as well as in three-dimensional models. In order to image the three-dimensional microstructure of the coating a synchrotron microto- mography was necessary. Because of the strong X-rays absorption from W, the measurement was a technical challenge. The tomographic reconstruction of a heterogeneous material where W has the main volume fraction required the design of a special sample geometry and the op- timization of several beam parameters at a high-energy beamline of the European Synchrotron Radiation Facility in Grenoble. Ein fortgeschrittenes numerisches Verfahren, basierend auf der Abbildung der Mikrostruktur (Image-Based Finite Element Method, Abk. Image-Based FEM ), wurde für die Modellierung des thermo-mechanischen Materialverhaltens neuer Fusionswerkstoffe weiterentwickelt. Zwei auf Wolfram als Hauptbestandteil basierende heterogene Materialien mit unterschiedlichen, zufälligen Morphologien auf mehreren Längenskalen wurden als Fallstudien ausgewählt: 1) gemischte duktil-spröde W/CuCr1Zr-Verbundwerkstoffe und 2) vacuum plasma-sprayed tung- sten (VPS-W 75 vol.%), ein plasmagespritztes poröses Beschichtungssystem mit einer zwei- skaligen Mikrostruktur. Beide Materialien sind für den Einsatz in dem zukünftigen Fusionsreak- tor DEMO geplant: W/CuCr1Zr-Verbundwerkstoff als Hauptbestandteil eines Gradienten- Übergangs und VPS-W als mögliche Lösung für die Beschichtung der ersten Reaktorwand mit unmittelbarem Plasmakontakt. Hauptziel der vorliegenden Arbeit war die numerische Modellierung von Materialversagen und Wärmetransport in Werkstoffen mit zufälliger Mikrostruktur durch Untersuchung des mesoskopischen und makroskopischen Werkstoffverhaltens. Besondere Beachtung wurde dabei der experimentellen Validierung von Simulationsergebnissen geschenkt. Direkte Simulation auf der realen Mikrostruktur ergab wichtige Erkenntnisse über den komplexen Versagensmecha- nismus beider Materialien. Für den W/CuCr1Zr Werkstoff wurde die gesamte Spannungs- Dehnungs-Kurve (inklusiv des Entfestigungs- und Versagensteils) bei unterschiedlichen Tem- peraturen berechnet und dabei eine gute Übereinstimmung mit experimentellen Daten gefun- den. Darüber hinaus konnten neue Möglichkeiten zur Bestimmung von meso- und mikroskaligen Material-Parametern aus dem experimentell ermittelten makroskopischen Verhalten hinsichtlich plastischer Verformung bzw. Versagen aufgezeigt werden. Sowohl die Wärmeleitung als auch das elastische Verhalten von VPS-W wurden umfassend untersucht. Neue mögliche Anwendungen des Image-Based FEM wurden hier damit gezeigt:quantitative Dekomposition des Beitrages der einzelnen morphologischen Phasen zur Behin- derung der Wärmeübertragung und Abschätzung der reduzierten Steifigkeit an den interlamel- laren Grenzflächen. Die Mikrostruktur realer VPS-W-Proben wurde sowohl bei der Entwicklung der planaren als auch der dreidimensionalen Modelle berücksichtigt. Um Zugang zu der realen dreidimensionalen Mikrostruktur zu gewinnen war eine Synchrotron-Mikrotomographie des Beschichtungssystems erforderlich. Wegen der starken Absorption von Röntgenstrahlung durch Wolfram war die to- mographische Messung eine technische Herausforderung. Die Tomographie eines heterogenen Materials mit Wolfram als Hauptanteil erforderte die Entwicklung einer speziellen Probenge- ometrie sowie die Optimierung mehrerer experimenteller Parameter an einer Hochenergetischen Beamline des European Synchrotron Radiation Facility in Grenoble.

This paper presents the recent progress in the pre-conceptual design activities for the EU-DEMO divertor Cassette Body, performed in the framework of the work package “Divertor” of the EUROfusion Power Plant Physics & Technology (PPPT) program. According to Systems Engineering Principles, the divertor CAD model is reviewed, considering the updates in the DEMO configuration model presented by the Programme Management Unit (PMU) in 2017. The design parameters affected by these changes and their impact on the divertor design and on the interfaced systems are analysed. Then, the paper focuses on the integration on the new cassette geometry of the divertor sub-systems. This includes the design of a “shielding liner” for cassette body and Vacuum Vessel protection, as well as the development of the cassette body-to-Vacuum Vessel fixation system. The design activities related to these main sub-systems are discussed in detail, in terms of CAD model and thermo-mechanical calculations.