Carbon-rich fuels—coal, petroleum, and natural gas—offer many advantages over other energy sources. They have a superior energy density relative to almost all other fuel sources, they have a wide range of use, and they are relatively easy to transport and to store. Often they are inexpensive relative to other fuels, particularly when existing infrastructure exists so that supply can meet demand. At the same time, fossil fuels present some downsides, particularly related to the environment and climate change. Over the last several years, there has been a growing consensus among climate scientists that nuclear energy is critical for mitigating the worst effects of global warming. Nations and states are shifting from Renewable Energy Mandates to technology-neutral Clean Energy Standards that include nuclear energy.
Nuclear power—with its high energy density and low carbon footprint—is a source with which the international community has decades of experience. However, the challenges that come along with the technology have kept it from becoming a more dominant factor in the global energy mix. Geopolitical issues lie at the center of many of these challenges. Matters of safety, waste management, and proliferation are intrinsic to the technology. Although the carbon footprint of using nuclear fuels is smaller, there are still disadvantages of using nuclear fuel. The waste, while a much lower volume must be handled very carefully because of its radioactivity. Nuclear fuels require far more complicated systems to extract their energy, which calls for greater regulation.
Concerns surrounding nuclear proliferation have been the cause of at least one war in the past ffteen years and have the potential to spark others. Competition among the exporters of civil nuclear technology has helped reduce the costs of nuclear power to consumers. However, it has also brought into question whether international regulations surrounding the construction, use, and export of nuclear technology are suffcient to ensure nuclear power is safe, secure, and proliferation resistant.
United States Department of Energy’s 2020 released report, Restoring America’s Competitive Nuclear Energy Advantage which says nuclear power is intrinsically tied to national security. America has lost its competitive global position as the world leader in nuclear energy to state-owned enterprises, notably Russia and China, with other competitor nations also aggressively moving to surpass the United States (U.S.). It has recommended a strategy comprising of addressing domestic and international security interests, expanding nuclear generation, minimizing commercial fleet fiscal vulnerabilities, assuring defense needs for uranium, and leveling the playing field against state-owned enterprises.
First, the U.S. Government will take bold action to revive and strengthen the uranium mining industry, support uranium conversion services, end reliance on foreign uranium enrichment capabilities, and sustain the current fleet, removing strategic vulnerabilities across the nuclear fuel cycle and restoring a world-class workforce to provide benefits to the U.S. and to compete in the international market. Next, the U.S. Government will leverage American technological innovation and advanced nuclear Research, Development, and Demonstration (RD&D) investments to accelerate technical advances and regain American nuclear energy leadership.
Finally, the U.S. Government will move into markets currently dominated by Russian and Chinese State Owned Enterprises (SOE) and recover our position as the world leader in exporting best-in-class nuclear energy technology, and with it, strong non-proliferation standards. We will restore American nuclear credibility and demonstrate American commitment to competing in contested markets and repositioning America as the responsible nuclear energy partner of choice. The Nuclear Fuel Working Group recognizes the importance of taking focused, deliberate action to prevent the near-term collapse of the domestic uranium mining, milling, and conversion industries and the need to support US strategic fuel cycle capabilities.
The safe and economical operation of any nuclear power system relies to a great extent, on the success of the fuel and the materials of construction. During the lifetime of a nuclear power system which currently can be as long as 60 years, the materials are subject to high temperature, a corrosive environment, and damage from high-energy particles released during fission. The fuel which provides the power for the reactor has a much shorter life but is subject to the same types of harsh environments. Understanding and overcoming material degradation in an extreme environment is essential for safe, efficient operation. New advanced materials may make plant construction more economical. Materials science plays a pivotal role in extending the life of existing nuclear reactors; in deploying new, modern light water reactors, advanced reactors with non-water coolants, and small modular reactors; and in storing, recycling, and disposing of used nuclear fuel.
A typical Light Water Reactor (LWR) contains numerous types of materials that must all perform successfully. For existing LWRs, extending the lifetime of each fuel element would improve the energy extraction from the fuel, limit the total amount of unused fuel (approximately 95% of the energy content remains at the end of the current useful life of a typical LWR fuel pin), and improve the overall economics of the plan.
Researchers from US, Europe, Russia, China, Germany and Japan are striving towards harnessing immense energy of nuclear fusion, the process that powers the Sun and produces 10 thousand times more energy than coal. The idea is to recreate the nuclear fusion that occurs in stars, where atomic nuclei collide and fuse together to form helium atoms, releasing huge amount of energy in the process.
Nuclear fusion—the reaction in which atomic nuclei collide—could provide a nearly unlimited supply of safe, clean energy, like that naturally produced by the sun through fusing hydrogen nuclei into helium atoms. Harnessing this carbon-free energy in reactors requires generating and sustaining a plasma, an ionized gas, at the very high temperatures at which fusion occurs (about six times hotter than the sun’s core) while confining it using magnetic fields. Not only does the fusion process expose reactors to extreme pressure and temperatures, helium — the byproduct of fusion between hydrogen atoms — adds to the strain placed on reactors by bubbling out into the materials and eventually weakening them. Of the many challenges currently facing fusion reactor demonstrations, is creating viable materials to build a reactor.
“The formidable materials challenges for fusion are where I saw an opportunity for my research—developing materials that can survive inside the fusion reactor, where the plasma will generate high heat fluxes, high thermal stresses, and high particle and neutron fluxes,” said Trelewicz Trelewicz—an assistant professor in the College of Engineering and Applied Sciences. “The operational conditions in this environment are among the harshest in which one could expect a material to function.”
Researchers from Texas A&M University, working with a team from the Los Alamos National Laboratory in New Mexico, have tested a new method for creating the materials used in nuclear fusion reactors and found that it could eliminate one of the obstacles preventing humanity from harnessing the power of fusion energy.
In 2017, DOE’s program awarded Designing new metal alloys using engineered nanostructures
A primary candidate for such “plasma-facing material” is tungsten, because of its high melting point—the highest one among metals in pure form—and low sputtering yield (number of atoms ejected by energetic ions from the plasma). However, tungsten’s stability against recrystallization, oxidation resistance, long-term radiation tolerance, and mechanical performance are problematic.
Trelewicz thinks that designing tungsten alloys with precisely tailored nanostructures could be a way to overcome these problems. In August, he received a $750,000 five-year award from the DOE’s Early Career Research Program to develop stable nanocrystalline tungsten alloys that can withstand the demanding environment of a fusion reactor. His research is combining simulations that model atomic interactions and experiments involving real-time ion irradiation exposure and mechanical testing to understand the fundamental mechanisms responsible for the alloys’ thermal stability, radiation tolerance and mechanical performance. The insights from this research will inform the design of more resilient alloys for fusion applications.
In addition to the computational resources they use at their home institution, Trelewicz and his lab group are using the HPC cluster at the CFN—and those at other DOE facilities, such as Titan at Oak Ridge Leadership Computing Facility (a DOE Office of Science User Facility at Oak Ridge National Laboratory)—to conduct large-scale atomistic simulations as part of the project.
Electron microscopy at the CFN has played a key role in an exciting discovery that Trelewicz’s students recently made: an unexpected metastable-to-stable phase transition in thin films of nanostructured tungsten. This phase transition drives an abnormal “grain” growth process in which some crystalline nanostructure features grow very dramatically at the expense of others. When the students added chromium and titanium to tungsten, this metastable phase was completely eliminated, in turn enhancing the thermal stability of the material.
In 2018, Rusian Scientists create new material for nuclear reactors
Today, zirconium alloys are the main material used in the fuel-element casings containing uranium oxide pellets. The material features high erosion and corrosion resistance in water, along with a low thermal neutron capture cross-section (the property characterizing the probability of chemical interaction between neutron particles and the atom nucleus).
However, zirconium alloys are also known to have several drawbacks, including the generation of heat in water and the production of hydrogen, which accelerates the degradation of the fuel-element casings. This occurs during zirconium-steam reactions, which take place when temperatures reach above 700 degrees Celsius, which can be very dangerous in emergency situations at water-cooled nuclear power stations. A zirconium-steam reaction is believed to have been one of the causes of the Fukushima Daiichi nuclear disaster in 2011.
Researchers from the National Research Nuclear University MEPhI (Russia) have conducted a study on the use of isotopically modified molybdenum as an alternative to zirconium alloys from which nuclear fuel-element casings are created. They have proved that this can enhance the safety of nuclear reactors. The study is published in the scientific journal Chemical Engineering Research and Design.
Nuclear physicists around the world have long discussed the possibility of replacing zirconium alloys with a refractory molybdenum alloy casing, which, like zirconium, has high corrosion resistance, but also higher thermal conductivity. The main drawback to the material has traditionally been its expense, which requires an increase in the degree of the uranium’s enrichment, and thus makes the technological process much more expensive.
However, Russian scientists believe they may have found a solution – change the natural composition of molybdenum isotopes, using centrifugal separation technology. Moreover it allows to create an alloy with thermal neutron capture cross-section figures similar to or even smaller than that of zirconium.
Valentin Borisevich, professor at MEPHI’s Department of molecular physics, told that the university’s study has provided researchers with “all the information necessary for the design of a separation system for the large-scale production of isotopically modified molybdenum on the basis of existing Russian technology for the separation of non-uranium isotopes in gas centrifuges.” If introduced, the technology could lead to substantial increases in nuclear power plant safety.
The university’s study was made possible thanks to support from the Russian Foundation for Basic Research, and in cooperation with the department of engineering physics at the Tsinghua University in Beijing, China.
A Helium-Resistant Material Could Finally Usher in the Age of Nuclear Fusion
Working with a team of researchers at Los Alamos National Laboratory in New Mexico, Demkowicz investigated how helium behaves in nanocomposite solids, materials made of stacks of thick metal layers. Their findings, recently published in Science Advances, were a surprise. Rather than making bubbles, the helium in these materials formed long channels, resembling veins in living tissues.
“We were blown away by what we saw,” Demkowicz said. “As you put more and more helium inside these nanocomposites, rather than destroying the material, the veins actually start to interconnect, resulting in kind of a vascular system.”
This discovery paves the way to helium-resistant materials needed to make fusion energy a reality. The most immediate application of this discovery, according to Demkowicz, is the development of fusion reactor materials designed to let helium flow out instead of remaining trapped inside reactors. The vein-like tunnels can serve as channels for helium to pass through, but Demkowicz believes that’s just the start.
“I think the bigger picture here is in vascularized solids, ones that are kind of like tissues with vascular networks,” he said. “What else could be transported through such networks? Perhaps heat or electricity or even chemicals that could help the material self-heal.”
In 2018, IAEA launched challenge on materials for fusion
The International Atomic Energy Agency (IAEA) has launched a competition to find “innovative ways to visualise, analyse and explore” simulations of different materials that can be used to build fusion reactors. Such materials would subject to extremely high temperatures and energetic particles.
The IAEA said the results of the challenge will be useful for the development of a demonstration fusion power plant. Such a plant would show that controlled nuclear fusion can generate net electrical power and mark the final step before the construction of a commercial fusion power plant. This would represent the next stage after ITER, the world’s largest fusion experiment under way, which is expected to demonstrate by the late 2030s that fusion can be used to generate net energy. It is not part of ITER’s mission to convert this energy into electricity.
“Harnessing commercially-viable fusion power involves serious technological challenges that are expected to take many years to solve, including protecting the wall and other components of the reactor vessel from extremely high temperatures and energetic particles,” the agency said.
Christian Hill, head of the IAEA’s atomic and molecular data unit, noted that obtaining a very high temperature in a reactor is one of the required conditions for fusion to take place. “At such high temperatures – ten times higher than at the core of our Sun – matter exists only as plasma, which must be confined by a magnetic field to keep it from damaging the reactor walls,” he said.
Candidate materials for use in fusion reactors include tungsten, steel and beryllium, the IAEA said. “Since experiments on physical samples are difficult and expensive to carry out, scientists have turned to computational models to simulate the behaviour of a material,” it said. “Different metals or compositions, impact energies and temperatures can be explored [using molecular dynamics] and can help with the search for an effective first wall material.”
The IAEA is inviting “experts and self-taught enthusiasts” to analyse simulations of the damage that can be caused to the reactor wall by the energetic neutrons released by the fusion reaction.
Participants are requested to submit ideas that take one or more of the following into consideration: novel software for visualising the material damage represented by the simulation data files in a way that aids qualitative and quantative assessment; new software tools to rapidly and reliably identify, classify and quantify new patterns and structures of particular kinds in the data sets; or, efficient algorithms to depict and summarise the statistical distribution of atom displacements and to analyse the effect of impact energy on this distribution.
Hill said, “By participating in this challenge, both specialists and non-specialists will be helping scientists to better understand how a material responds to high-energy events and will assist the development of a future fusion reactor.”
In 2019, US DOE discovered Tiny granules can help bring clean and abundant fusion power to Earth
Beryllium is one of the two main materials used for the wall in ITER, a multinational fusion facility under construction in France to demonstrate the practicality of fusion power. Now, physicists from the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and General Atomics have concluded that injecting tiny beryllium pellets into ITER could help stabilize the plasma that fuels fusion reactions.
Experiments and computer simulations found that the injected granules help create conditions in the plasma that could trigger small eruptions called edge-localized modes (ELMs). If triggered frequently enough, the tiny ELMs prevent giant eruptions that could halt fusion reactions and damage the ITER facility.
In the present experiments, the researchers injected granules of carbon, lithium, and boron carbide—light metals that share several properties of beryllium—into the DIII-D National Fusion Facility that General Atomics operates for the DOE in San Diego. “These light metals are materials commonly used inside DIII-D and share several properties with beryllium,” said PPPL physicist Robert Lunsford, lead author of the paper that reports the results in Nuclear Materials and Energy. Because the internal structure of the three metals is similar to that of beryllium, the scientists infer that all of these elements will affect ITER plasma in similar ways. The physicists also used magnetic fields to make the DIII-D plasma resemble the plasma as it is predicted to occur in ITER.
These experiments were the first of their kind. “This is the first attempt to try to figure out how these impurity pellets would penetrate into ITER and whether you would make enough of a change in temperature, density, and pressure to trigger an ELM,” said Rajesh Maingi, head of plasma-edge research at PPPL and a co-author of the paper. “And it does look in fact like this granule injection technique with these elements would be helpful.”
If so, the injection could lower the risk of large ELMs in ITER. “The amount of energy being driven into the ITER first walls by spontaneously occurring ELMs is enough to cause severe damage to the walls,” Lunsford said. “If nothing were done, you would have an unacceptably short component lifetime, possibly requiring the replacement of parts every couple of months.”
Lunsford also used a program he wrote himself that showed that injecting beryllium granules measuring 1.5 millimeters in diameter, about the thickness of a toothpick, would penetrate into the edge of the ITER plasma in a way that could trigger small ELMs. At that size, enough of the surface of the granule would evaporate, or ablate, to allow the beryllium to penetrate to locations in the plasma where ELMs can most effectively be triggered.
The researchers envision the injection of beryllium granules as just one of many tools, including using external magnets and injecting deuterium pellets, to manage the plasma in doughnut-shaped tokamak facilities like ITER. The scientists hope to conduct similar experiments on the Joint European Torus (JET) in the United Kingdom, currently the world’s largest tokamak, to confirm the results of their calculations. Says Lunsford, “We think that it’s going to take everyone working together with a bunch of different techniques to really get the ELM problem under control.”
In May 2020, New Alloy Material Approved for Use in High-Temperature Nuclear Plants
The American Society of Mechanical Engineers recently added Alloy 617 into its Boiler and Pressure Vessel Code. The new addition is the sixth material cleared for use in high-temperature reactors and could allow new designs to operate at even higher temperatures. The milestone ends a successful decade-long project by the U.S. Department of Energy (DOE) that consisted of researchers from Argonne, Oak Ridge and Idaho National Laboratories (INL). “It’s a pretty substantial accomplishment,” said INL Project Manager Richard Wright. “This means designers working on new high-temperature nuclear plants now have 20% more options when it comes to component construction materials.”
Alloy 617 is a combination of nickel, chromium, cobalt and molybdenum. It was first developed for use in high-temperature gas reactors, but can also be applied to molten salt and liquid metal reactor designs. The new metal offers significant improvements over previously approved alloys in the code and can withstand operating temperatures of 1,750◦ Fahrenheit—nearly 400 degrees hotter than the next-best material.
The expanded operating range gives advanced reactor developers more flexibility when choosing materials to build their high-temperature systems. The new designs could also open up new market opportunities for the nuclear industry by using its thermal heat to directly heat communities, drive industrial processes, produce hydrogen, and even purify water without emitting carbon.
Getting a new material into the code is a lengthy process and requires significant amounts of data. The national labs spent years testing the material properties of Alloy 617 in order to qualify the metal for commercial use. Alloy 617 was added to the code in the fall of 2019 and is the first high-temperature material cleared for commercial use since the 1990s. DOE invested $15 million over 12-years to make Alloy 617 available in support of the demonstration and deployment of advanced reactor concepts.
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