Speaker
Tobias Wegener
(Institut für Energie- und Klimaforschung – Plasmaphysik)
Description
Tungsten is considered the main candidate material for the first-wall in DEMO for its high melting point, low erosion yield and low fuel retention. Nevertheless, it can cause a substantial safety issue in a loss-of-coolant accident (LOCA) in combination with air ingress into the plasma vessel, due to formation and evaporation of volatile neutron activated tungsten oxide. Self-passivating tungsten alloys introduce a passive safety mechanism by forming a stable chromic oxide layer on the surface acting as a diffusion barrier for oxygen and preventing the formation of tungsten oxide.
In this contribution self-passivating tungsten alloys optimised for oxidation resistance containing 12wt.% chromium and ~0.4wt.% yttrium are investigated under conditions of argon-oxygen, argon-water and nitrogen-oxygen-water atmospheres at different partial pressures and temperatures ranging from 1073 to 1473K. Thin films with 3.5µm thickness produced by magnetron sputtering are used as a model system. The oxidation resistance of theses films in an argon-20vol.% oxygen atmosphere is sufficient to prevent formation and release of tungsten oxide for more than 60h at 1073K, and for 2.5h at 1273K to up to 9h by doubling the film thickness. All following the favoured parabolic oxidation regime. Assuming an armour thickness of 2mm, mitigation of tungsten oxide release for several years under the conditions of a LOCA with air ingress is predicted. In argon-water the alloy shows linear oxidation behaviour without release or formation of tungsten oxide within 2h at 1273K. The evaporation of chromium in nitrogen-oxygen-water atmosphere at ≤1273K will be discussed.
A deeper understanding of the governing processes for oxygen/chromium diffusion under different atmospheres will be shown, supported by SEM/TEM/EDX, XRD, TGA and SIMS measurements. Furthermore, the production of W-Cr-Y bulk-samples is ongoing using mechanical alloying. The plasma performance and thermo-mechanical characteristics of these bulk-samples will be presented.
Co-authors
Andrey Litnovsky
(Institut für Energie- und Klimaforschung – Plasmaphysik, IEK-4, Partner of the Trilateral Euregio Cluster (TEC), Forschungszentrum Jülich GmbH, Jülich, Germany)
Christian Linsmeier
(Institut für Energie- und Klimaforschung – Plasmaphysik, IEK-4, Partner of the Trilateral Euregio Cluster (TEC), Forschungszentrum Jülich GmbH, Jülich, Germany)
Felix Klein
(Institut für Energie- und Klimaforschung – Plasmaphysik, IEK-4, Partner of the Trilateral Euregio Cluster (TEC), Forschungszentrum Jülich GmbH, Jülich, Germany)
Freimut Koch
(Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany)
Jens Brinkmann
(Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany)
Marcin Rasinski
(Institut für Energie- und Klimaforschung – Plasmaphysik, IEK-4, Partner of the Trilateral Euregio Cluster (TEC), Forschungszentrum Jülich GmbH, Jülich, Germany)
Tobias Wegener
(Institut für Energie- und Klimaforschung – Plasmaphysik, IEK-4, Partner of the Trilateral Euregio Cluster (TEC), Forschungszentrum Jülich GmbH, Jülich, Germany)
