The breadth and coverage of analytical expertise in the IEA Technology Collaboration Programmes (TCPs) are unique assets that underpin IEA efforts to support innovation for energy security, economic growth and environmental protection. The 39 TCPs operating today involve about 6 000 experts from government, industry and research organisations in more than 50 countries1.
Nuclear Technology Fusion Reactors (NTFR TCP)
Improving fusion sustainability with lithium pebbles
The NTFR TCP conducts research experiments on key components of fusion power plants, in particular those close to the fusion plasma. As tritium is a rare element, it will need to be recycled from the plasma for fusion to be economically viable. Activities under this TCP found that lithium pebbles offer an innovative, low-cost approach to recycling tritium.
Lithium pebbles used to extract tritium from the fusion process, one of the promising materials for the future DEMO reactors (left: pebbles, right: pebble surface).*
Developing materials that can resist extreme heat radiating from the plasma is a challenging task from a scientific and engineering viewpoint. For fusion to be achieved, we need to understand how to contain – and maintain – hot plasma. The next step will be to learn how to extract (“breed”) fuel (“tritium”) from the hot plasma in order to regenerate the fusion ignition. Technology plays a critical role in accomplishing this task through components lining the wall called “blanket modules”. Several materials for blanket modules have been examined to date, both solid and liquid, and a variety of blanket module concepts have been considered ranging from more conservative concepts to higher-risk higher-payoff concepts for future reactors. The major candidate breeding materials consist of liquid breeders, mainly liquid metals, although more recently some attention has been given to multi-materials such as steel/lithium/beryllium and lithium ceramic breeders.
A recent advance for breeding tritium is through ceramic pebbles containing lithium. Lithium meta-titanate (Li2TiO3) pebbles are being considered as one of the most promising tritium breeding materials for future DEMO reactors because of its reasonable lithium atom density, prominent tritium release rate at low temperatures, its low activation characteristics, low thermal expansion coefficient and high thermal conductivity.
For these reasons, the participants in the NTFR TCP working group “Characterization of newly developed ceramic breeder pebbles” launched round-robin tests of pebble samples in facilities of each of the participants (China, Europe, India, Japan, and Korea). They set out to characterise the optimal chemical composition, fabrication method, and thermal and mechanical properties of tritium breeder pebbles under fusion conditions in order to establish benchmarks.
In China, experiments focused on optimising the present fabrication process, researching the fundamental character of ceramic pebbles, and enhancing the tritium release properties of ceramic pebbles to supplement the tritium breeder database. In India, the test facility is based on the principal of steady state and axial heat flow methods, aiming to develop tritium breeder material by solid state reaction and solution combustion method. In the EU (Karlsruhe Institute of Technology, Germany) the EU test facility is based on the hot wire method**. In Japan, experiments aimed to define accurate understandings of the vaporisation properties from the breeder materials, the measurements in proper temperature ranges are required. Korea focused research on the fabrication methods. A slurry droplet wetting method was effective based on the cross-linking reaction between PVA and boric acid.
These results have greatly improved the thermo-mechanical design of the ITER Test Blanket Modules, which are the key technology of the fusion DEMO reactors to extract high performance, safe and clean energy from the fusion reaction.
- Liquid breeding blankets
- Plasma-facing components
- Plasma surface interactions
- Solid breeding blankets
- Tritium processing
For more information: the NTFR IA website is under development.
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