The Elements of Innovation Discovered
The Elements of Innovation Discovered
Metal Tech News - February 1, 2023
Tokamaks such as this one use powerful magnetic forces to confine plasma during a fusion reaction.
While tungsten's high-melting point and toughness make it a good candidate for fusion reactors, it can become brittle. To overcome this weakness, scientists are creating alloys with other metals, such as nickel and iron.
The International Thermonuclear Experimental Reactor (ITER) project recently reported hitting significant snags in its quest to prove the feasibility of fusion as a large-scale and carbon-free source of energy.
Fusion entails forcing together the nuclei of light atomic elements in a super-heated plasma, held by powerful magnetic forces in a doughnut-shaped chamber called a "tokamak."
By fusing the particles together from isotopes of hydrogen, which can be extracted from seawater, researchers at ITER hope to create a safer and almost inexhaustible form of energy than the current method for generating nuclear energy, which requires splitting atoms from uranium or plutonium.
The ITER scientists had hoped to create the plasma by 2025.
But ITER's director-general Pietro Barabaschi told a reporter in early January that the achievement will be delayed not only because two major problems have surfaced but also the original target date "wasn't realistic."
One new obstacle was the wrong sizes ordered for the joints of blocks to be welded together for the installation's 19-by-11-meter (62-by-36-feet) chamber.
The second new problem is traces of corrosion found in a thermal shield designed to protect the outside world from the enormous heat created during nuclear fusion.
Fixing the problems "is not a question of weeks, but months, even years," according to Barabaschi.
ITER researchers plan to develop a new timetable by the end of 2023, he said, including some modifications to contain the expected cost overrun, and to meet the French nuclear safety agency's security requirements.
Barabaschi said he hoped ITER would be able to make up for the delays as it prepares to enter the full phase, currently scheduled for 2035.
The ITER project was set in motion after a 1985 summit between U. S. President Ronald Reagan and Soviet leader Mikhail Gorbachev.
Its seven partners are China, the European Union, India, Japan, South Korea, Russia, and the United States.
Russia still participates in ITER despite the ongoing Ukraine conflict.
In November, the country dispatched one of six giant magnets needed for the top part of the tokamak.
At the end of 2022, researchers at Lawrence Livermore National Laboratory in California reported observing a net energy gain through nuclear fusion for the very first time. They said the achievement is a monumental milestone toward fusion energy that could power homes and businesses with a carbon-neutral energy source. But converting this scientific achievement into a practical power source also requires new technologies to make a fusion-powered society a reality.
Barabaschi said ITER's researchers welcomed the news that the U. S. scientists working separately had made an important technical breakthrough.
A team at the Lawrence Livermore National Laboratory in California Dec. 13 reported using the world's largest laser to create, for the first time, a fusion reaction generating more energy than it took to produce.
"Some competition is healthy in any environment," Barabaschi said about the success.
"If tomorrow somebody found another breakthrough that would make my work redundant, I would be very happy," he added.
A team of Scientists at Pacific Northwest National Laboratory, and Virginia Polytechnic Institute and State University, meanwhile reported progress in their efforts to bring this goal to fruition through materials research. The recent work, outlined in a research paper published Jan. 24 in "Scientific Reports," makes a case for tungsten heavy alloys and shows how they can be improved for use in advanced nuclear fusion reactors by mimicking the structure of seashells.
"This is the first study to observe these material interfaces at such small length scales," said Jacob Haag, first author of the research paper. "In doing so, we revealed some of the fundamental mechanisms which govern material toughness and durability."
The sun – with a core temperature of around 27 million degrees Fahrenheit – is powered by nuclear fusion. Thus, it should come as no surprise that fusion reactions produce a lot of heat. Before scientists can harness fusion energy as a power source, they need to create advanced nuclear fusion reactors that can withstand high temperatures and irradiation conditions that come with fusion reactions.
Of all the elements on Earth, tungsten has one of the highest melting points. This makes it a particularly attractive material for use in fusion reactors. However, it can also be very brittle. Mixing tungsten with small amounts of other metals, such as nickel and iron, creates an alloy that is tougher than tungsten alone while retaining its high melting temperature.
It isn't just their composition that gives these tungsten heavy alloys their properties – thermomechanical treatment of the material can alter properties like tensile strength and fracture toughness.
A particular hot-rolling technique produces microstructures in tungsten heavy alloys that mimic the structure of nacre, also known as mother-of-pearl, in seashells. Nacre is known to exhibit extraordinary strength, in addition to its beautiful iridescent colors. The PNNL and Virginia Tech research teams investigated these nacre-mimicking tungsten heavy alloys for potential nuclear fusion applications.
"We wanted to understand why these materials exhibit nearly unprecedented mechanical properties in the field of metals and alloys," said Haag.
To get a closer look at the microstructure of the alloys, Haag and his team used advanced materials characterization techniques, such as scanning transmission electron microscopy to observe atomic structure. They also mapped the nanoscale composition of the material interface using a combination of energy-dispersive X-ray spectroscopy and atom probe tomography.
Within the nacre-like structure, the tungsten heavy alloy consists of two distinct phases: a "hard" phase of almost pure tungsten, and a "ductile" phase containing a mixture of nickel, iron, and tungsten. The research findings suggest that the high strength of tungsten heavy alloys comes from an excellent bond between the dissimilar phases, including intimately bonded "hard" and "ductile" phases.
"While the two distinct phases create a tough composite, they pose significant challenges in preparing high-quality specimens for characterization," said Wahyu Setyawan, PNNL computational scientist and co-author of the paper. "Our team members did an excellent job in doing so, which enables us to reveal the detailed structure of interphase boundaries as well as the chemistry gradation across these boundaries."
The study demonstrates how crystal structure, geometry, and chemistry contribute to strong material interfaces in tungsten heavy alloys. It also reveals mechanisms to improve material design and properties for fusion applications.
"If these bi-phase alloys are to be used in the interior of a nuclear reactor, it is necessary to optimize them for safety and longevity," said Haag.
The researchers said the findings presented in the study are already being further expanded upon in many dimensions within the PNNL and scientific research community. Multiscale material modeling research is underway at PNNL to optimize structure, chemistry, and to test the strength of dissimilar material interfaces, as well as experimental investigations to observe how these materials behave under the extreme temperatures and irradiation conditions of a fusion reactor.
"It is an exciting time for fusion energy with renewed interests from the White House and the private sectors. The research that we do in finding material solutions for prolonged operations is critically needed to accelerate the realization of fusion reactors," said Setyawan.
Additional PNNL authors are Jing Wang (formerly of PNNL), Karen Kruska, Matthew Olszta, Charles Henager, Danny Edwards, and Mitsu Murayama, who also holds a joint appointment with Virginia Tech.
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