MEPhI: Solder TiZr4Be for soldering tungsten with steel

2022: Announcement of TiZr4Be solder for tungsten soldering with steel

On August 15, 2022, representatives from the National Nuclear Research University MEPhI reported that university scientists proposed a way to connect plasma-facing reactor wall materials.

DEMO

As reported, the demonstration thermonuclear reactor (DEMO) will be the next stage in preparation for the use of thermonuclear energy on an industrial scale. The first stage is the France International Thermonuclear ITER Experimental Reactor (International Thermonuclear Experimental Reactor) under construction near Marseille. possibility of using thermonuclear energy for peaceful purposes. If this succeeds, humanity will receive an almost inexhaustible source of energy. Next Generation Reactors DEMO some member countries, including number and, Russia will be built already on its territory - it will have to react with even greater power and in almost continuous mode.

In ITER, all materials for the construction of the reactor have already been identified and the first experiments on it should begin in 2025, while DEMOs exist so far only in the form of theoretical developments. For installations of the DEMO type, it is necessary develop and implement complex elements and systems that are not available on any experimental thermonuclear devices existing for August 2022.

One of the main problems that will need to be solved is the choice of material for the most energetically stressed, thermonuclear plasma-contacting elements of the DEMO reactor. If in ITER the base of the walls is chromocyrconium bronze with soldered "tiles" made of tungsten or beryllium, then in DEMO, where the loads on the reactor walls will be much more powerful, you will need already heat-resistant steel - it is assumed that in the domestic installation it will be either austenitic or ferritic-martensitic steel EK-181 (according to the Western classification of Rusfer). However, among others, a serious problem remains - it is necessary to create a heat-resistant integral joint of steel and tungsten for the elements of the first wall and diverters of the future reactor, which will be under loads above 2 MW/m2 and neutron irradiation.

For this purpose, it was necessary not only to obtain another solder alloy from low-activated elements and to work out the modes of soldering tungsten with steel, but also to understand the fields of application of such solder compounds in the medium of hydrogen isotopes - fuel of thermonuclear reactors. This was done by a group of scientists at NRNU MEPhI: by joint efforts of the departments of physical problems materials science and plasma physics was developed by solder TiZr4Be for soldering tungsten with steel EK-181 and the conditions for the use of such solder compounds in a hydrogen medium were determined.

Since the materials must also be low-activated, 2/3 of the Mendeleev table cannot be used in such installations. It is necessary to develop solder with a certain melting point and choose a soldering mode that would allow you to combine very different materials in their properties, in particular by the coefficient of thermal expansion - tungsten and steel. Otherwise, with rapid temperature changes, cracks may occur in the joint and the plasma-facing reactor wall elements will simply collapse. told Alexey Suchkov, Associate Professor, Institute of Nuclear Physics and Technology, NRNU MEPhI

The fuel of fusion reactors is a mixture of isotopes of hydrogen, deuterium and tritium, the latter can accumulate in wall materials. In addition to the accumulation of radioactive tritium from a safety point of view, there is a problem hydrogen embrittlement of the material, which means that specific solders that are stable in hydrogen are needed. As a result of research the Russian by scientists, it was found that solder TiZr4Be with an intermediate layer of tantalum can method is used to connect tungsten with low-activated ferritic-martensitic steel.

Deuterium retention in W-EK-181 joints and individual elements was investigated with emphasis on the intermediate layer of solder. The samples were exposed to deuterium gas (p = 1-104 Pa, T = 300-600 ° C) and plasma discharge (T = 600 ° C). A comprehensive analysis of the condition of samples after exposure was carried out, including when using a synchrotron radiation source. After plasma irradiation and after gas exposure at a pressure of 1 Pa, an acceptable deuterium concentration was observed, which corresponds to the operating conditions of future thermonuclear devices. However, with increased pressures, the capture of deuterium became too large, which led to the destruction of the solder and the entire soldered joint.

We took the first step: we created a layout of the element of the first wall of the thermonuclear reactor and the divertor, and tested it in modes close to those expected in thermonuclear installations. The compound is stable under certain conditions - we have identified its limitations on the temperature and pressure of the surrounding gas. Therefore, it is necessary either to continue the search for suitable materials, or to ensure acceptable operating conditions. continued Yuri Gasparyan, Associate Professor, Institute of Laser and Plasma Technologies, NRNU MEPhI

The work was carried out with grants from the Russian Science Foundation and the Ministry of Science and Higher Education. The contribution of Russian scientists to the creation of ITER and the design of the next generation of reactors DEMO is decisive: the initiative to create the first international experimental thermonuclear installation belonged to academician E.P. Velikhov, it is based on the tokamak system (Toroidal Chamber with Magnetic Coils), also developed in the 50s of the twentieth century by Soviet academicians I.E. Tamm and A.D. Sakharov. As of August 2022, the largest scientific centers of Russia - the Kurchatov Institute, NRNU MEPhI, VNIINM, TRINITIES, NIIEFA, NIKIET and others - were involved in the project, and, despite the sanctions, scientific international cooperation in this area continues.

The results of the work are published in the scientific journal Journal of Nuclear Materials.