Russian researchers from the Troitsk Institute for Innovation and Fusion Research (TRINITI – part of Rosatom’s Scientific Division) and the National Research Nuclear University (NRNU MEPhI) have proposed an innovative way to reduce impurities in thermonuclear plasma to protect fusion reactor walls from erosion.
The temperature of the plasma in a thermonuclear installation can be many times higher than the temperature at the centre of the Sun. Flows of energy and particles from the plasma and its unstable behaviour can damage the inner wall, and evaporated wall particles then cool the plasma, which negatively affects the course of the thermonuclear reaction.
The researchers have proposed making the internal surfaces of the reactor from tungsten. However, tungsten can also be damaged by contact with plasma. The proposed protection method involves diffusion saturation of the tungsten surface with boron atoms. As a result, protective layers of borides – chemical compounds of boron and tungsten (high-temperature materials) are formed on the inner wall of the reactor.
According to Sergei Ipatov, Deputy General Director of LLC RARMA (a scientific and production association that specialises in high-tech innovations for science-intensive industries), the borated layer on the surface of tungsten should mitigate the main drawback of this metal – the entry of multiply charged impurities into the tokamak plasma. A surface protected in this way has an unusual property: microcracks that occur during powerful thermal shocks close themselves by melting boron oxides to form a glassy phase.
Yuri Gasparyan, head of the Department of Plasma Physics at NRNU MEPhI said the researchers had conducted comparative tests of tungsten samples, similar to the one from which the inner surface of the ITER reactor will be made, as well as test samples of tungsten with a diffusion coating. Thermal shock tests carried out on a quasi-stationary plasma accelerator installation for generating high-speed plasma flows showed that the threshold for damage by irradiation with hydrogen isotopes to the surface of tungsten with a borated layer at a temperature of 1300-1500 degrees С is higher than for tungsten without the coating.
When simulating plasma failures, it was found that the rate of erosion of tungsten with a borated layer is less than the erosion of pure tungsten. Moreover, boron in the coating composition acts as an effective oxygen absorber. As a result, a borated layer of tungsten surface 0.1 mm thick can reduce impurities in thermonuclear plasma for the entire period of operation of the ITER reactor. In this case, it will not be necessary to use the glow discharge boronisation system that is currently being designed.
Anatoly Krasilnikov, Director of Rosatom’s ITER Project Centre praised the work being done by researchers and recommended further study of boron-containing diffusion coatings for plasma-facing elements. “As part of cooperation with China in the field of thermonuclear reactors, we will test our new development in the near future on the EAST tokamak with the aim of using it on China’s BEST tokamak, currently under construction and scheduled to be completed in 2027. The next stage will be ITER.”
According to TRINITI Chief Designer Pavel Piskarev, the development also has potential for use in the projected Russian tokamak with reactor technologies (TRT). “Technologies for creating heat-removing panels of the first wall with tungsten cladding have been developed and well mastered in our country as part of participation in the ITER project. The use of borated tungsten instead of pure tungsten does not require radical change to established production chains and can be easily implemented, while the potential benefits are enormous.”
The research work will be published in the upcoming issues of Atomic Science and Technology (VANT – Voprosy Atomnoy Nauki i Tekhniki).
RARMA is a research and production association with divisions in Moscow, Chelyabinsk and its own production site in Lipetsk. It specialises in innovations in the fields of metallurgy, laser technologies, industrial engineering of automated and robotic solutions, as well as in the production of high-tech products from special steels.
