Nuclear fusion as a source of energy for stars was described in the 1920s .
Since then, scientists have not stopped dreaming of reproducing this process in a controlled way.
Nuclear fusion as a source of energy for stars was described in the 1920s . Since then, scientists have not stopped dreaming of reproducing this process in a controlled way.
Generating energy through fusion is emulating 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 precisely, finding the materials that will be able to contain nothing less than a star.
Materials that do not yet exist
To date, nothing supports the extreme conditions of irradiation and temperature in the walls of a nuclear fusion reactor and we find ourselves with technical limitations to characterize materials that do not yet exist. So we have to invent them and, to find out if they work, put them to the test.
To characterize them, we need experimental facilities to see how they behave under irradiation conditions similar to those expected in a fusion reactor. That is the objective of macro projects such as the IFMIF-DONES (International Fusion Materials Irradiation Facility ) that is underway.
Creating new materials, materials that don’t yet exist, and that can withstand the process is another daunting challenge.
We have to integrate physical phenomena that occur on the most diverse dimensional scales, from nanometers, as in the case of radiation-induced defects, to millimeters or centimeters, as occurs in the propagation of fissures/cracks. Also at different time scales, from picoseconds to days, months or even years. To test such diversity, we employ multiscale computational simulation techniques on supercomputers.
Computer simulations are a virtual laboratory for research and development of new materials for fusion. A clear example whose development was accelerated with these techniques are nanoporous metals
Nanoporous metals: a metal sponge
To imagine how nanoporous metals are, let’s think of a kitchen sponge, full of holes of visible size. That same sponge, if it were made of metal and with the same void/material ratio as the original but each one 1,000 times smaller than a hair, would be a nanoporous metal and would have about a quarter of a trillion of these pores.
In these materials, the total surface area of the pores is greater than the area of a football field, and all in the volume of a kitchen sponge. In this particularity lies its potential for many technological applications .
And why are we interested in this? Because surfaces are sinks for radiation-induced defects.
The extreme radiation conditions in a fusion reactor induce innumerable defects in the crystal lattice of the material. If these defects are close to a free surface, they migrate to it and escape from the material. Thus, nanoporous metals theoretically have the potential to self- heal.
From the IMDEA Materials Institute we entered the field of materials for fusion with the Mechanics of Nanoporous Wunder irradiation ( MeNaWir ) project, financed by the European Atomic Energy Community (Euratom) and the Marie Skłodowska-Curie Actions (MSCA) program .
At MeNaWir we create computational models to simulate the behavior of metals under the working conditions of reactors. Thus, we can evaluate and find materials that resist these adverse conditions.
As a strategy, we have chosen a multiscale computational framework for the exploration of the mechanical properties of materials for melting, and we have focused on nanoporous refractory metals, in particular nanoporous tungsten .
Tungsten has the highest melting point of all metals, at around 3,400 degrees, is highly resistant to heat and wear, and is one of the least susceptible metals to the effects of radiation .
However, even tungsten may not be enough to withstand the harsh radiation and temperature conditions in melting applications. Thus, what is proposed to study is tungsten with a nanoporous, sponge-like microstructure.
Nanoporous tungsten would combine the excellent mechanical properties in extreme environments of its base material with a nanostructure that facilitates the migration to the surface of all induced defects caused by radiation.
long term impact
The development of computational techniques to simulate the behavior of materials for fusion reactors entails clear benefits for the nuclear industry: a computational selection and evaluation of materials, greatly reducing the number of tests to be carried out in real conditions .
In MeNaWir, the computational framework to be developed has a multiscale basis and is specifically oriented to study the mechanical behavior of nanoporous metals under the extreme conditions of fusion reactors.
With this framework it would be possible, for example, to determine a window of optimal microstructures for the conditions of these reactors. Moreover, the impact of the development of these simulation techniques could also be applied to other cases with great technical interest and close working conditions, for example, the study of nanoporous metals in generation IV fission reactors and small modular reactors .
If it works, we would have found nothing less than material capable of containing a star on Earth.