Development of joining technologies for their aplication in fusion reactors

Development of joining technologies for their aplication in fusion reactors

The fossil fuels that shaped 19th and 20th century civilization can only be relied on at the cost of greenhouse gases and pollution. Therefore, a new large-scale, sustainable and carbon-free form of energy is urgently needed. The following advantages make fusion worth pursuing: abundant energy, sustainability, no CO₂ emission, no long-lived radioactive waste, limited risk of proliferation and no risk of meltdown. Besides, the power output of the kind of fusion reactor that is envisaged for the second half of this century will be similar to that of a fission reactor (i.e. between 1 and 1.7 gigawatts).

The present research line is part of a project of the European consortium EUROfusion, funded by Euratom within the Horizon 2020 program. EUROfusion supports fusion research activities in accordance with the Roadmap to the realization of fusion energy. The research is focused on the manufacturing and characterization of joints of first wall (FW) and divertor components of the future DEMO (DEMOnstration Power Station) fusion reactor. The components and materials used in the FW will be exposed to high thermal loads, among other relevant phenomena, which will take place inside the vacuum vessel (i.e. neutron irradiation, particles exposure, etc.). The FW design includes a tungsten layer, which will face the plasma and protect the other materials from the most adverse conditions. The layer will be joined to a low activation ferritic/martensitic steel (Eurofer). The function of the divertor is to extract heat and helium ash, as well as other impurities from the plasma to allow the incorporation of new fuel for the fusion reaction. This component has to withstand high heat and neutron fluxes and thermal loads of 10 MW/m2. For the main plasma facing units of the divertor, experiencing the most direct heat loading, several design solutions are under consideration. Most assume a tungsten monoblock, receiving the heat flux on its top surface, with a CuCrZr tube carrying pressurized water through the block.
In the present proposal, W-Eurofer and W-CuCrZr joints will be developed using different fillers. The microstructural characterization of the joints will be carried out by optical and scanning electron microscopy. The mechanical properties will be evaluated by Vickers microhardness, nanoindentation, shear tests, etc. Base materials are joined by brazing and Rey Juan Carlos University research group collaborates with other Research Units in the characterization of the joints. I.e. joints are exposed to high heat fluxes (HHF tests are made in collaboration with the Forschungszentrum Jülich, Germany).

The proposal offers the experienced researcher a secondment in CIEMAT (Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas). During a period of three months, the researcher will complete the characterization of the joint interfaces by transmission electron microscopy (TEM) using the focused ion beam technique (FIB) that is an ideal tool for TEM sample preparation.