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Developing fusion is an extremely difficult scientific and engineering challenge. 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 the energy from that plasma in order to generate electricity. Technology plays a critical role in our ability to accomplish this important task. Support for further research will be necessary to reap the rewards of fusion: large-scale electricity generation without greenhouse gas emissions.
The goals of the Implementing Agreement for a Co-operative Programme on Nuclear Technology of Fusion Reactors (NTFR IA) are to conduct research experiments on key components of fusion power plants and associated technologies, in particular those operating close to the fusion burning plasma, or plasma-facing components. In particular, the NTFR IA works to develop effective, reliable, functioning components with prolonged lifetimes under the conditions expected to occur in a commercial fusion power plant. This is crucial to the economic performance and environmental and safety acceptability of fusion power. There are eight Contracting Parties, including China, India and Russia.
Two isotopes of hydrogen are used to fuel the fusion reaction – deuterium and tritium. Deuterium can be extracted from seawater but the worldwide supply of tritium is currently estimated at 20 kilograms. Yet when neutrons escaping the fusion plasma interact with lithium contained in the blanket, tritium is produced. This concept of 'breeding' tritium during the fusion reaction is an important one for the future needs of a large-scale fusion power plant.
Mock-ups of devices to extract the tritium, called Test Blanket Modules (TBM), simulate tritium breeding in a real fusion environment. The TBM shield the chamber walls from the high temperatures and the high-energy neutrons. In the blanket, the neutrons are slowed down so their kinetic energy can be transformed into heat, which will in turn be used to create electricity.
Testing plasma-facing components such as TBM is one of six research areas of the NTFR IA. Important recent progress was made in two main areas of R&D related to the ITER TBM Programme, neutron irradiation and tritium production.
The NTFR IA recently completed neutron irradiation tests on ceramic breeder pebbles. These pebbles have been irradiated by neutrons over several years in order to achieve conditions relevant to the post-ITER power plant, DEMO. The test results will be used to improve the design of both the ITER TBM programme and the DEMO blanket.
In the blanket design, evaluation of tritium production and recovery are critical. However, experimental data of tritium production are lacking. To improve this situation, NTFR IA members carried out fusion neutron irradiation tests at a level of 14 megaelectron volts (MeV) on lead-lithium liquid breeder materials and ceramic breeder pebbles.
These measurements are important to establish benchmarks. Data from these experiments will be collected and shared via the data bank of the OECD Nuclear Energy Agency.
* Photo courtesy of the Italian National Agency for New Technologies.
For more information: the NTFR IA website is under development.
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