High Temperature Materials Laboratory (HML) - Material tests under extreme loads
The High Temperature Materials Laboratory (HML) is an essential part of the research infrastructure of the IFN-1, offers worldwide unique opportunities for material and component testing and collaborates with national and international organizations in the frame of bi- and multilateral projects (e.g. ITER, Fusion for Energy – F4E, EUROfusion, JET, ...). The emphasis of the research in the HML is put on experiments for the characterization of materials and components for the First Wall and Divertor of the actually built or planned fusion devices ITER and DEMO, respectively.
These plasma facing materials and components experience severe loading conditions due to plasma-wall interaction. These comprise on the one hand high steady state loads of 10 MW/m2 with excursions for several seconds of up to 20 MW/m2 during the cyclic operation of the facility. On the other hand, normal and off-normal transient thermal loads occur, which deposit within milliseconds or sub-milliseconds energy densities in extreme cases up to a maximum of about 50 MJ/m2 on part of the plasma facing wall and in particular in the strike-point area of the divertor. Furthermore, high particle loads occur by hydrogen isotopes deuterium and tritium as well as helium, coming from the fuel and the fusion reaction.
Besides these high thermal and particle loads in future fusion devices in addition the materials will be exposed to high energetic neutrons, which deposit their energy, in contrast to the before mentioned loads, not at the surface bus as volumetric load. These neutrons influence the mechanical and thermo-physical properties and cause, depending on the material and loading conditions, volumetric changes of the material. Therefore, characterizing neutron irradiated materials is an essential step in the qualification process for the use in fusion devices as well as a prerequisite for design and life-time analyses.
Those loading conditions put high demands on the material selection and the production processes during component manufacturing, in particular the joining of similar and dissimilar materials. Accordingly, high heat flux tests by means of the electron beam facilities JUDITH 2 und JUDITH 3 are performed successfully to qualify the materials and the reliability of components with respect to failure mechanisms and life-time. JUDITH 2 with a maximum power of 200 kW is used for the investigation of larger components or semi-prototypes as well as for the application of transient loads at high frequency on actively cooled material samples outside of the hot cells.
IR-images of thermo-shock specimens in the electron beam facility JUDITH 2; surface roughening and crack formation after thermo-shock at 70°C coolant temperature (left) and during cooling down including macro-cracks (right)
In the existing hot cells at HML-2 as well as the new hot cell complex actually being installed in HML-3 investigations on neutron activated materials are performed to determine neutron induced material modification and degradation. Therefore, material specimens and small components are neutron irradiated in European and international material test reactors as well as future large-scale devices for the generation of fusion relevant 14 MeV neutrons (e.g. DONES) and subsequently investigated at the HML.
Irradiation Samples with irradiation capsule in preparation for inserting into the material test reactor.
Until 2019 and after almost three decades of operation high heat flux tests were performed in the electron beam facility JUDITH 1. After several years of planning this will now be continued by the construction of new hot cells at the HML-3 and the operation of the 60 kW electron beam facility JUDITH 3, which has been already commissioned outside the hot cells. In addition, the linear plasma facility JULE-PSI will be operated as well in an adjacent hot cell as nuclear “twin” of the already existing PSI-2 facility. Both facilities, JUDITH 3 and JULE-PSI, are worldwide unique and allow the investigation of synergistic effects in one laboratory. For the qualification and quantification of the results microscopic and metallographic means for post-mortem analyses are also available in the hot cells of HML-2.
SEM-images of tungsten after thermo-shock loading in JUDITH 2
Weitere Erweiterungen der Möglichkeiten der Nachbestrahlungscharakterisierung insbesondere im Hinblick auf die Charakterisierung der thermo-physikalischen Eigenschaften mittels Laserflash und Differential Scanning Kalorimetrie als auch im Hinblick auf die Wasserstoffrückhaltung in den Materialien mittels der Anlage FREDIS, die bereits im HML mit schwach aktiven Proben betrieben wird, sind derzeit in Planung bzw. Bau.
A further extension of the options for post-irradiation examination is actually planned or under construction. This concerns in particular the characterization of thermo-physical properties via laserflash and differential scanning calorimetry. Moreover, hydrogen retention is investigated in the facility FREDIS, which is operated at the HML amongst others with low activated tritium containing material specimens.
FREDIS device for thermal (left; TDS-furnace at 800°C) and laser-induced (right; tungsten sample during laser pulse) desorption spectroscopy
Based on the existing expertise in the HML in the field of high temperature materials, besides the various nuclear fusion related activities also contributions to projects for other industrial applications have been made during the last two decades. These comprise e.g. the development of x-ray anodes, ceramic insulators in the conventional power plant technology, high temperature ceramics of the metal industry, and insulating materials for space applications.
