The choice of the material of the reactor's inner wall facing the hot plasma is one of the key and still unresolved tasks in creating a thermonuclear reactor. A group of Russian researchers from the Rosatom Scientific Institute in Troitsk (part of the Scientific Division of Rosatom State Corporation), RARMA LLC (Lipetsk) and the National Research Nuclear University MEPhI proposed an innovative way to reduce impurities in thermonuclear plasma and protect reactor walls from erosion.
Photo from the ITER website
The plasma temperature in a fusion plant can be many times higher than the temperature in the center of the Sun. The flows of energy and particles from the plasma and its unstable behavior can damage the inner wall, and the evaporated particles of the wall "cool" the plasma, which negatively affects the course of the thermonuclear reaction.
Scientists have proposed a solution to a problem previously considered unsolvable – making the inner surfaces of the reactor from tungsten. Tungsten is the most refractory of metals, but it can also be damaged by contact with plasma. The proposed method of protection consists in diffusive saturation of the tungsten surface with boron atoms. As a result, protective layers of borides, chemical compounds of boron and tungsten, which belong to the class of high-temperature materials, are formed on the inner wall of the reactor. According to Sergey Ipatov, Deputy General Director of RARMA LLC, the borated layer on the surface of tungsten should smooth out the main drawback of this metal – the ingress of multiply charged impurities into the plasma of the tokamak. An unusual property appears on the surface protected in this way: microcracks that occur during powerful thermal shocks are independently closed by melting boron oxides to form a glassy phase.
According to Yuri Gasparyan, Head of the Department of Plasma Physics at the National Research Nuclear University MEPhI, PhD, the creators of the development conducted comparative tests of tungsten samples, similar to the one from which the inner surface of the ITER reactor will be made, and test samples of tungsten with a diffusion coating. Thermal shock tests conducted at a quasi–stationary plasma accelerator (KSPU), an installation for generating high-speed plasma flows, showed that the threshold for damage to the surface of tungsten with a boron layer at a temperature of 1300-1500 ° C is higher than that of tungsten without coating by irradiation with hydrogen isotopes.
When simulating plasma disruptions, 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 acts as an effective oxygen absorber. Due to this, a boronized layer of a tungsten surface with a thickness of 0.1 mm can reduce impurities in the thermonuclear plasma for the entire period of operation of the ITER reactor. At the same time, it will not be necessary to use a glow discharge harrowing system, which is currently being designed.
Anatoly Krasilnikov, Director of the ITER Design Center at Rosatom State Corporation, Ph.D., highly appreciated the work done by the scientists and made recommendations for further research of boron-containing diffusion coatings for plasma-facing elements. "As part of cooperation with China in the field of thermonuclear reactors, in the near future it is necessary to test our new development on the existing EAST tokamak in order to use it on the BEST tokamak, which is scheduled to be completed in China in 2027. The next stage is the international reactor ITER," he shared.
Pavel Piskarev, Chief Designer of the Rosatom Scientific Institute in Troitsk, noted the promising development and the high significance of the results in relation to use in the projected Russian tokamak with reactor technologies (TRT). "Technologies for creating heat-dissipating panels of the first wall with tungsten cladding have been developed and well mastered in our country as part of the ITER project. The use of boronated tungsten instead of pure does not require drastic processing of established production chains and can be easily implemented, while the potential advantages are enormous," he said.
The publication of the work is planned in the next issues of the journal "Issues of Atomic Science and Technology" (VANT).
