Nuclear fusion: what material can a star on Earth contain?

Nuclear fusion as a source of energy for stars was described as early as the 1920s, and since then, scientists have never stopped dreaming of reproducing this process in a controlled way.

Fusion power generation mimics what the Sun does, but on Earth and inside a container. One of the bottlenecks to achieve this is the design of this container, and more specifically, the search for materials that can contain nothing more than a star.

Materials not yet available

To date, nothing supports the extreme irradiation conditions and temperatures in the walls of a fusion reactor, and we are faced with technical limitations to characterize materials that do not yet exist. So we have to invent them and put them to the test to see if they work.

To characterize them, we need experimental setups to see how they behave under irradiation conditions like those expected in a fusion reactor. This is the goal of macro projects such as IFMIF-DONES (International Fusion Irradiation Facility) which is underway.

Creating new materials, materials that do not yet exist that can withstand this process, is another challenge.

We have to integrate physical phenomena occurring at a wide variety of scales, from nanometers, as in the case of radiation defects, to millimeters or centimeters, as occurs with the propagation of cracks/cracks. Also on different time scales, from picoseconds to days, months or even years. To test this diversity, we use multiscale computational simulations on supercomputers.

Computer simulation is a virtual laboratory for the research and development of new materials for thermonuclear fusion. A prime example that has been accelerated by these methods is nanoporous metals.

Nanoporous metals: metal sponge

To imagine how nanoporous metals are, let’s imagine a kitchen sponge full of visible holes. The same sponge, if made of metal and with the same void/material ratio as the original, but each 1,000 times smaller than a hair, would be a nanoporous metal and have about a quarter of a trillion such pores.

In these materials, the total surface area of ​​the pores is larger than the area of ​​a football field, and all in the volume of a kitchen sponge. In this feature lies its potential for many technological applications.

And why are we interested in it? Because the surfaces are sinks of radiation defects.

The extreme radiation conditions in a fusion reactor cause innumerable defects in the material’s crystal lattice. If these defects are close to the free surface, they migrate to it and exit the material. Thus, nanoporous metals theoretically have the potential for self-healing.

tungsten values

From the IMDEA Institute of Materials, we entered the field of fusion materials with the Mechanics of Nanoporous Wunder irradiation (MeNaWir) project funded by the European Atomic Energy Community (Euratom) and the Marie Skłodowska-Curie Action Program (MSCA).

At MeNaWir, we create computational models to simulate the behavior of metals under reactor operating conditions. In this way, we can evaluate and find materials that are resistant to these adverse conditions.

As a strategy, we chose a multiscale computational framework for studying the mechanical properties of fusible materials and focused on nanoporous refractory metals, in particular, nanoporous tungsten.

Tungsten has the highest melting point of any metal, around 3400 degrees, is very resistant to heat and wear, and is one of the least susceptible metals to radiation.

However, even tungsten may not be enough to withstand the harsh radiation and temperature conditions of smelting. Thus, tungsten with a nanoporous spongy microstructure is proposed for study.

The nanoporous tungsten will combine the excellent mechanical properties of the base material under extreme conditions with a nanostructure that facilitates the migration of all radiation-induced defects to the surface.

long term impact

The development of computational methods for simulating the behavior of materials for fusion reactors has clear advantages for the nuclear industry: the computational selection and evaluation of materials, which greatly reduces the amount of testing carried out in real conditions.

In MeNaWir, the developed computing base has a multiscale basis and is specifically focused on studying the mechanical behavior of nanoporous metals under extreme conditions of thermonuclear reactors.

With this structure, it would be possible, for example, to determine the window of optimal microstructures for the conditions of these reactors. In addition, the impact of the development of these simulation techniques can also be applied to other cases of great technical interest and similar operating conditions, such as the study of nanoporous metals in generation IV fission reactors and small modular reactors.

If it worked, we would find nothing less than a material capable of supporting a star on Earth.

Carlos J. Ruestes, MSCA Research Fellow, Materials Modeling and Characterization, IMDEA MATERIALS, and Javier Segurado, University Professor, POLITICAL UNIVERSITY OF MADRID MADRID // Senior Research Fellow, Multiscale Materials Modeling, IMDEA MATERIALS

This article was originally published on The Conversation. Read the original.

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