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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.
Nuclear fuel is the fuel that is used in a nuclear reactor to sustain a nuclear chain reaction. Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. These fuels are fissile, and the most common nuclear fuels are the radioactive metals uranium-235 and plutonium-239. Heat is created when nuclear fuel undergoes nuclear fission. Nuclear fuel has the highest energy density of all practical fuel sources. All processes involved in obtaining, refining, and using this fuel make up a cycle known as the nuclear fuel cycle.
Scientists at the Department of Energy’s Idaho National Laboratory have a new fuel called Advanced Nuclear Energy for Enriched Life, or ANEEL. It’s a proprietary mix of thorium and low-enriched uranium, and Forbes’s James Conca says it could help close the gap in a near future where nuclear seems like the only option. So having a new fuel made in America that can be used in reactors in other countries brings the United States back into play in the nuclear supply chain, and allows us to reach more of the nations around the world.
Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoing and sustaining nuclear fission. The three most relevant fissile isotopes are uranium-233, uranium-235 and plutonium-239. When the unstable nuclei of these atoms are hit by a slow-moving neutron, they split, creating two daughter nuclei and two or three more neutrons. These neutrons then go on to split more nuclei. This creates a self-sustaining chain reaction that is controlled in a nuclear reactor, or uncontrolled in a nuclear weapon.
Worldwide, there are extensive reserves of uranium left to mine. While nuclear fuel is not renewable, it is sustainable since there is so much of it. It will run out eventually, but not for centuries. Unlike fossil fuels, using nuclear fuels to produce energy does not directly produce carbon dioxide or sulfur dioxide. It should be mentioned that the processes of mining, transporting, and refining the fuel have carbon emissions associated with them, comparable to those of wind and solar power.
Though much attention has been focused on the exciting realm of nuclear reactor technology innovation, major efforts to improve nuclear fuels—and boost power generation safety and economics—are underway. Dr. Tatiana Ivanova, a long-time nuclear engineer and head of the Nuclear Science division at Paris-based intergovernmental organization Nuclear Energy Agency (NEA), why so much activity is ongoing to transform nuclear fuel—and her answer is simple: “It is the principal part of nuclear power plants.” Fuel design optimization is “a cornerstone for the industry to deploy new, modern fuel for light-water reactors [LWRs], advanced reactors, and small modular reactors,” she said. “Also, it is a very important part in storing, recycling, and disposing of used nuclear fuel. That is why a study of performance and reliability of nuclear fuel have remained a high priority in the research portfolios of all nuclear countries.”
Safety, perhaps, has been the foremost driver of rapid fuel design optimization. As Fukushima showed, “because of the highly exothermic nature of zirconium-steam reactions, under some low-frequency accidents [when core cooling is temporarily lost and part of the core is uncovered], low-probability accidents may lead to an excess generation of heat and hydrogen, resulting in undesirable core damage,” Ivanova said. That’s why in 2014, the NEA, a specialized agency within the Organisation for Economic Co-operation and Development (OECD), jumped into action to gauge the interest of its of its 33 member countries in the exploration of enhanced accident-tolerant fuels (ATF) for LWRs, she said.
Activity is especially notable in the U.S., where the Department of Energy (DOE) aggressively implemented plans under its Congressionally mandated Enhanced Accident Tolerant Fuel program. As the DOE notes, the urgency is underscored by nine recent reactor retirements, many for economic reasons. Much of the U.S. nuclear fleet, in particular, already have 60-year operating licenses that will expire in the 2030s, and getting these new fuels to market before then would increase the performance of these reactors and ultimately improve their chances of applying for extended operation with the Nuclear Regulatory Commission (NRC), it said.
Over the past few years Russia has also been working hard to develop new nuclear fuels for VVER and fast reactor units. In 2016, MORE THAN 250 specialists from more than 30 organisations attended a conference in Russia on New Generation Nuclear Fuel for NPPs — Development, Operating experience and Future Directions. The conference, organised by fuel company Tvel (part of state nuclear corporation Rosatom), was held at the AA Bochvar Research Institute of Inorganic Materials (VNIIMN), a leading Russian centre for nuclear fuel research. It covered current developments and recommended a series of research and development (R&D) directions for new nuclear fuel.
“Today we are working in several key areas in the development and improvement of fuel for NPPs,” Pyotr Lavrenyuk, Tvel’s senior vice president for scientific and technical activities, technology and quality control told the delegates. “First of all, Tvel continues to improve VVER reactors, and improve the quality of zirconium materials. Next year we will focus on developing fast reactor fuel. Rosatom has set an ambitious goal for us to significantly increase the operating time and the percentage of fuel burnout.”
At the 2016 conference, a separate decision was made to develop and improve technical documentation for fuel elements and fuel assemblies of various types, as well as structural materials, nuclear fuel and its components. The resolution paid particular attention to the development of new promising types of fuel, including Remix (regenerated mixture), mox (mixed uranium-plutonium oxide), and MNUP (mixed nitride uranium-plutonium) fuel.
What’s notable, she explained to POWER in February, is that all LWRs around the world currently use fuel systems comprising uranium oxide (UO2) encased within a zirconium-based alloy cladding (and to a much smaller degree, some reactors use uranium-plutonium oxide, or mixed-oxide [MOX] fuels). Over many decades, this oxide fuel-zircaloy system has been optimized, it has matured, and it has generally met all performance and safety requirements. But over the last 10 years, a rapidly changing sector has required a transformation—an urgent revival that starts at that core, with safety and economics as key priorities, she said.
Nuclear Fuels
Uranium-235 is used as a fuel in different concentrations. Some reactors, such as the CANDU reactor, can use natural uranium with uranium-235 concentrations of only 0.7%, while other reactors require the uranium to be slightly enriched to levels of 3% to 5%. Plutonium-239 is produced and used in reactors (specifically fast breeder reactors) that contain significant amounts of uranium-238. It can also be recycled and used as a fuel in thermal reactors. Current research is being done to investigate how thorium-232 can be used as a fuel.
For fission reactors, the fuel (typically based on uranium) is usually based on the metal oxide; the oxides are used rather than the metals themselves because the oxide melting point is much higher than that of the metal and because it cannot burn, being already in the oxidized state.
Fuel fabrication plants are facilities that convert enriched uranium into fuel for nuclear reactors. For light water reactors, uranium is received from an enrichment plant in solid form. It is then converted into a gas and chemically converted into a uranium dioxide powder. This powder is then pressed into pellets and packed into fuel assemblies. A mixed oxide fuel can also be created when the uranium powder is packed along with plutonium oxide. The hazards present at fuel fabrication facilities—mainly chemical and radiological—are similar to the hazards at enrichment plants. These facilities generally pose a low risk to the public.
When used in a reactor, the fuels used can have a variety of different forms a metal, an alloy, or some sort of oxide. Most nuclear reactors are fueled with a compound known as uranium dioxide. This uranium dioxide is put together in a fuel assembly and inserted into the nuclear reactor—where it can stay for several months or up to a few years. While in the reactor the fuel undergoes nuclear fission and releases energy. This released energy is used to generate electricity. Neutrons released during the fission process allow for a fission chain reaction to occur, allowing energy to be generated continually. The fuel is removed from the reactor after large amounts of the fuel—whether it is uranium-235 or plutonium-239—have undergone fission. The “used” nuclear fuel is known as spent or irradiated fuel. After use, the fuel must be cooled for a few years as it is extremely hot.
The spent fuel is placed in large, deep pools of water that act as a coolant and a radiation shield. The coolant property allows the water to remove the decay heat and the shielding abilities protect workers from the radioactivity of the fuel. After cooling, the fuel can be re-purposed or sent to storage depending on regulations.
Liquid fuels are liquids containing dissolved nuclear fuel and have been shown to offer numerous operational advantages compared to traditional solid fuel approaches. Liquid-fuel reactors offer significant safety advantages due to their inherently stable “self-adjusting” reactor dynamics. This provides two major benefits: – virtually eliminating the possibility of a run-away reactor meltdown, – providing an automatic load-following capability which is well suited to electricity generation and high-temperature industrial heat applications.
For miltary nuclear weapons the main material is highly enriched uranium (HEU), containing at least 20% uranium-235 (U-235) and usually about 90% U-235. HEU can be blended down with uranium containing low levels of U-235 to produce low-enriched uranium (LEU), less than 5% U-235, fuel for power reactors. It is blended with depleted uranium (mostly U-238), natural uranium (0.7% U-235), or partially-enriched uranium.Highly-enriched uranium in US and Russian weapons and other military stockpiles amounts to about 1500 tonnes*, equivalent to about seven times annual world mine production.
World stockpiles of weapons-grade plutonium are reported to be some 260 tonnes, which if used in mixed oxide fuel in conventional reactors would be equivalent to a little over one year’s world uranium production. Military plutonium can blended with uranium oxide to form mixed oxide (MOX) fuel.
New Nuclear Fuel initiatives
Under the DOE’s program that today casts a wide net of collaboration that includes several U.S. utilities, universities, and the Electric Power Research Institute (EPRI), the DOE is funding and technically backing several industry-led ATF fuel concepts, including fuel pellet and cladding materials developed by GE-Hitachi joint venture Global Nuclear Fuel (GNF), Westinghouse, General Atomics, and Framatome. The vendors must ensure an initial lead test assembly has been installed in a U.S. commercial power plant, and that prototypic pin segments have been installed in the Idaho National Laboratory’s (INL’s) Advanced Test Reactor’s (ATR’s) water loop by 2023, and have full cores licensed for higher burns by 2026.
Among notable projects are tests of GNF’s iron-chromium-aluminum fuel cladding material known as “IronClad” and coated zirconium fuel cladding known as “ARMOR” at Southern Nuclear’s Edwin I. Hatch Nuclear Plant in Georgia, which are slated to end in March 2020. In January, the company also installed IronClad and ARMOR materials at Exelon’s Clinton plant in Illinois. In April 2019, Exelon’s Byron Unit 2 in Illinois completed installation of Westinghouse’s EnCore Fuel, which encapsulates chromium-coated zirconium cladding for enhanced oxidation and corrosion resistance; higher-density ADOPT pellets—which are chromia (Cr2O3) and alumina (Al2O3) doped UO2-pellets—for improved fuel economics; and uranium silicide pellets.
Also in April 2019, Framatome completed installation of four GAIA lead fuel assemblies containing enhanced ATF (EATF) pellets and cladding—advanced chromium coating that is added to its proprietary M5 zirconium-alloy cladding—at Southern Nuclear’s Vogtle 2 in Georgia. As Framatome explained, the combination “improves high-temperature oxidation resistance and reduces hydrogen generation during loss of cooling.” The chromium coating, meanwhile, also “greatly reduces creep to maintain a coolable geometry and has mechanical properties that allow for more operator response time. Further, the innovative coating offers increased resistance to debris fretting during normal operations.” The company told POWER in early February that it is now in “early manufacturing stages” for delivering complete fuel assemblies—full-length chromia-coated rods and chromium-enhanced pellets—to Exelon’s Calvert Cliffs reactor in Maryland in 2021.]
Around the world, meanwhile, TVEL, Russian state-owned corporation Rosatom’s nuclear fuel fabrication and supply arm, last October loaded two experimental ATF fuel assemblies with VVER (a Russian-designed water-cooled, water-moderated reactor) and pressurized water reactor (PWR) fuel rods at its MIR research reactor at the State Research Institute of Atomic Reactors in the Ulyanovsk Region.
TRISO Particles: The Most Robust Nuclear Fuel on Earth
TRISO stands for TRi-structural ISOtropic particle fuel. Each TRISO particle is made up of a uranium, carbon and oxygen fuel kernel. The kernel is encapsulated by three layers of carbon- and ceramic-based materials that prevent the release of radioactive fission products. The particles are incredibly small (about the size of a poppy seed) and very robust. They can be fabricated into cylindrical pellets or billiard ball-sized spheres called “pebbles” for use in either high temperature gas or molten salt-cooled reactors.
TRISO fuels are structurally more resistant to neutron irradiation, corrosion, oxidation and high temperatures (the factors that most impact fuel performance) than traditional reactor fuels. Each particle acts as its own containment system thanks to its triple-coated layers. This allows them to retain fission products under all reactor conditions. Simply put, TRISO particles cannot melt in a reactor and can withstand extreme temperatures that are well beyond the threshold of current nuclear fuels.
TRISO fuel was first developed in the United States and United Kingdom in the 1960s with uranium dioxide fuel. In 2002, the Department of Energy (DOE) focused on improving TRISO fuel using uranium oxycarbide fuel kernels and enhancing its irradiation performance and manufacturing methods in order to further develop advanced high-temperature gas reactors.
In 2009, this improved TRISO fuel set an international record by achieving a 19% maximum burnup during a three-year test at Idaho National Laboratory (INL). This is nearly double the previous mark set by the Germans in the 1980s and is three times the burnup that current light-water fuels can achieve—demonstrating its long-life capability.
The irradiated fuel was then exposed to more than 300 hours of testing at temperatures up to 1800° Celsius (more than 3,000° Fahrenheit). These tests exceeded the predicted worst-case accident conditions for high-temperature gas reactors and showed no to minimal damage of the particles with full fission product retention. Continued TRISO fuel qualification testing is currently underway at INL. With support from DOE, the Electric Power Research Institute worked with INL and industry stakeholders to submit a licensing topical report to the U.S. Nuclear Regulatory Commission (NRC) for official review. Future test results will be submitted to the NRC for licensing TRISO fuel and reactor vendors.
TRISO fuel testing is gaining a lot of interest from the advanced reactor community. Some reactor vendors such as X-energy and Kairos Power, along with the Department of Defense, are planning to use TRISO fuel for their designs—including some small modular and micro-reactor concepts. DOE is also supporting X-energy’s efforts to design and submit a NRC license application for a new fabrication facility. The project would ultimately use high assay low enriched uranium to produce the TRISO fuel pellets and pebbles for future high-temperature gas and molten salt reactors.
VVER Fuel Innovations
Framatome, a French nuclear technology giant, notably credited its rapid development for GAIA, a PWR solution, to DOE support and favorable conditions in the U.S. market—including its competitive electricity markets, which demand large cost reductions. “This demand drives for more efficient designs,” it said. The U.S. fleet, which is committed to lifetime extensions, is also receptive to new innovative technologies, it noted. Among other fuel offerings Framatome is advancing in the U.S. market is ATRIUM 11, an 11 x 11 fuel rod array for boiling water reactors (BWRs), whose “unique geometry” inherently boosts safety, fuel cycle savings, as well as plant flexibility capabilities. Since it launched the ATRIUM 11 fuel in the U.S. in April 2015, two unnamed reactors have begun producing power using it, and Framatome recently bagged contracts to deliver ATRIUM 11 to Talen Energy’s Susquehanna plant in Pennsylvania by 2021, and to the Tennessee Valley Authority’s Browns Ferry plant in 2023.
According to Framatome, positive market signals are especially imperative to the development of advanced fuel designs because it is an intensely complex process. Contrary to perceptions that fuel assemblies are produced in a specific plant, “the entire supply chain is global,” it noted. Meanwhile, far from being a commodity, “nuclear fuel assemblies are a highly engineered and complex product built to extremely demanding quality standards,” and they are often “designed to operate flawlessly in an aggressive environment for many years,” the company noted. And though “great advancements” in digital and additive manufacturing have helped improve fuel systems, the industry often bears critical risks, such as those associated with funding, regulations, and with its supply chain.
A World of VVER Fuel Innovations—and Beyo
U.S. Government Made a Powerful New Kind of Nuclear Fuel
The United States Department of Energy (DOE) Idaho National Laboratory (INL) and the Nuclear Engineering & Science Center at Texas A&M have partnered with Clean Core Thorium Energy (CCTE) to fabricate a new type of nuclear fuel, called “Advanced Nuclear Energy for Enriched Life”, or ANEEL.
With a proprietary combination of thorium (Th) and uranium (U), particularly “High Assay Low Enriched Uranium” (HALEU), ANEEL fuel can address several issues that have plagued nuclear power – cost, proliferation and waste. Plus, this fuel, being made-in-America, positions it as a prime candidate for export to emerging nuclear markets.
The ANEEL fuel has a very high fuel burn-up rate of about 55,000 MWd/T (megawatt-day per ton of fuel) as compared to natural uranium fuel used in currently operating PHWRs/CANDUs with a burn-up of around 7,000 MWd/T. This is important in a few ways. Higher burn-up means the fuel stays in the reactor longer and gets more energy out of the same amount of fuel. Also, more neutron poisons breed in over the fuel’s use, including Pu-240,241,242 making the spent fuel prohibitively difficult to make into a weapon.
Also, a higher fuel burn-up of ANEEL fuel will reduces the waste by over 80% and ends up with much less plutonium (Pu) because more of the Pu is burned to make energy while making the spent fuel proliferation resistant. Less spent fuel means less refueling, less cost, less fuel handling and less volume to dispose. In addition, PHWR/CANDU reactors don’t have to be shut down to refuel, and can be refueled at full power. The Kaiga Unit-1 Indian PHWR, and Darlington Unit 1 in Canada, hold the world records for continuous operation at 962 days and 963 days of uninterrupted operation, respectively.
In an existing CANDU/PHWR using natural uranium, each fuel bundle weighs roughly 15 kg. After the first 150 days of operation, an average of eight such bundles would need to be replaced daily for the rest of the reactor’s operating life of 60 years. With the ANEEL fuel, each fuel bundle weighs approximately 10.65 kg. After the first 1,400 days of operation, an average of only one such bundle would need be replaced daily for the remainder of the reactor’s operating life, leading to significantly less waste.
Dr. Sean McDeavitt, Nuclear Engineering Professor and Director of the Nuclear Engineering & Science Center at Texas A&M University, notes, “I’ve been actively working on and around nuclear fuel behavior and applications for over 25 years. The ANEEL fuel concept integrated with the existing CANDU/PHWR reactor technology takes advantage of thorium’s superior properties, performance, and abundance to generate clean base-load electricity with reduced environmental impact.”
Texas A&M will fabricate the ANEEL fuel pellets at their Nuclear Engineering and Science Center and deliver them to INL. INL will conduct high burn-up irradiation testing of the ANEEL fuel pellets (up to 70,000 MWd/T) in INL’s accelerated test rig at their Advanced Test Reactor. This will be followed by post irradiation examination and fuel qualification, all under the stringent guidelines and quality assurance requirements of the DOE and the NRC.
“Today, emerging countries and their citizens, ever hungry for the power needed to drive the engines of progress and prosperity, need an abundant and uninterruptible source of clean base-load power. This solution must address multiple key barriers, including cost, efficiency, and sustainability,” says Mehul Shah, CEO and Founder of CCTE. “The urgency of realizing such a vision becomes even more critical as time is lost in the face of an accelerating climate crisis.”
References and Resources also include:
https://www.powermag.com/a-new-frontier-for-nuclear-fuels/
https://www.forbes.com/sites/jamesconca/2020/09/22/aneel-a-game-changing-nuclear-fuel/#55536fc014ea
