Wearing a T-shirt emblazoned with the words, “fission is my mission,” Dasari V. Rao, the director of Los Alamos National Laboratory’s Civilian Nuclear Program, is optimistic about the future of nuclear energy. Rao says recent advances in nuclear fission reactor technology, both at the Lab and across the globe, are paving the way for a solution to climate concerns.
Research on nuclear fission is not new to Los Alamos. In fact, it dates back to the Manhattan Project, the United States’ secret mission to split the atom, harness its power, and build the world’s first atomic bombs. Today, scientists at Los Alamos are delving into the next generation of nuclear fission breakthroughs. Researchers are uncovering new ways to use the process discovered more than 80 years ago to meet the nation’s energy needs.
Current work at the Lab involves research into the development of new fuels and materials for both existing and newly developed nuclear reactors. Another key area involves the design of small modular reactors and microreactors. These concepts offer the possibility of portable, easy-to-produce reactors that can meet a variety of energy needs—including the possibility of fueling deep-space exploration or powering human habitats on the moon or Mars.
“The Lab’s ability to make new types of reactor fuel and work with industry to build efficient reactor designs will lead to success,” Rao says. “Nuclear power is essential for producing affordable clean energy.”
What is nuclear fission?
Fission takes place when a neutron slams into a larger atom, splitting the larger atom into two smaller atoms. Additional neutrons are also released during the collision, which initiates a chain reaction of splitting atoms—or fissions. When each atom splits, a tremendous amount of energy is released.
Nuclear reactors contain and control the nuclear fission process while releasing heat at a controlled rate. Nuclear power plants transform the energy that the reactors release into electricity. Currently, all commercial nuclear reactors (called light-water or conventional reactors) built in the United States use uranium dioxide as fuel with water as a moderator that helps slow down the neutrons produced by fission. The fission creates heat, and the power plant uses that heat to turn water into steam, which then turns a turbine to produce electricity. The reactor core (where the fissions take place) must be kept cool or the nuclear fuel will overheat and melt. Water is used as a coolant.
Built in 1942 at the University of Chicago, the first fission reactor, called Chicago Pile-1, generated the first self-sustaining fission reaction. Nuclear reactors constructed during the Manhattan Project were used to produce the uranium and plutonium that would eventually go into the Fat Man and Little Boy atomic bombs. At the same time, scientists were exploring the energy applications of nuclear fission. After the war, in 1951, an experimental reactor in Idaho generated the first electricity from nuclear energy. In 1954, the United States used the same approach to launch the first nuclear-powered submarine, and the U.S. Navy operates a nuclear-powered submarine program today.
In 1955, the Atomic Energy Commission announced a program to develop nuclear power plants. During the 1960s and ’70s, more than 100 commercial reactors went into operation in the United States.
The decades of decline
Although the nuclear industry started off strong in the United States, that growth soon plateaued. The U.S. Energy Information Administration (EIA) reports that nuclear reactors were responsible for only 19–20 percent of the total annual U.S. electricity generation from 1990 through 2021. As of August 1, 2023, the United States had 93 operating commercial nuclear reactors at 54 nuclear power plants in 28 states. The newest reactors, which are in Georgia, began operation in July 2023, but most reactors are older, with an average age of 42 years. The oldest commercial reactor, located in New York, began operation in December 1969.
What slowed the growth of the industry? Scientists admit that nuclear energy has always suffered from an image issue. “With fission reactors, the big problem we have had is the tie-in with nuclear weapons, which leads to negative perceptions,” Rao says.
Safety concerns are also part of the problem. Rao explains that three high profile nuclear reactor accidents have colored public opinion. “The incidents at Three Mile Island [the 1979 partial meltdown in Pennsylvania], Chernobyl [the 1986 incident in Russia caused by flawed reactor design and operator errors], and Fukushima Daiichi [the 2011 meltdown in Japan that occurred when a tsunami disabled cooling ability] caused a lot of panic.”
These incidents led to increased regulatory oversight, which slowed the industry’s growth but also prompted scientists to improve reactor technology and fuel. Rao notes that “we have solved many of the safety issues that caused concern in the past.”
Hand in hand with problems related to public perception of nuclear reactor safety are worries about nuclear waste. Nuclear reactors produce no greenhouse gasses; however, they do create radioactive waste. This waste is primarily from used nuclear fuel, which is a solid both going into the reactor and coming out. When the used fuel is removed from the reactor, it is cooled in steel-lined concrete pools of water and then stored in dry sealed casks made of steel, concrete, or other protective shielding. Currently the casks are stored at individual reactor sites.
"This is the next generation of nuclear energy and one of the best solutions for climate issues.”
- Josh White
Time and money are the final roadblocks to embracing nuclear energy. Constructing massive nuclear reactor-fueled power plants is expensive and time consuming. The newest reactors built in Georgia ran $17 billion over budget and were completed seven years behind schedule, according to ABC News. “What company is willing to invest $10 to $20 billion, wait up to 10 years to turn on the plant and then wait for 20 years to recover that money?” Rao asks. Many new nuclear energy inventions are targeting ways to solve that problem, he adds.
The future of fuels
One of the ways Los Alamos scientists are making light-water reactors safer and more efficient is by developing accident tolerant fuels. “We’re developing fuels with higher thermal conductivity to eliminate problems if a plant loses its cooling ability, which is what happened in the Fukushima incident,” says Scarlett Widgeon Paisner, a research and development scientist. “Developing composites using existing fuels—such as uranium dioxide—and researching high-density fuels are ways we can enhance both safety and efficiency of the reactors.” Paisner points out that new fuels require extensive testing and must adhere to rigorous government regulations. “We have to know exactly how each fuel behaves under every condition possible, both normal and off-normal conditions.”
I expect that microreactors will be pretty big game changers going forward.”
—Dasari V. Rao
Along with boosting safety, the new fuels have the added benefit of increasing reactor efficiency, which adds to commercial viability, according to Rao. “By using more advanced fuels, you can make more power from the same amount of fuel—denser and better fuels that are safer and have real financial merits,” he says.
The development of new fuels is also impacting the actual design, structure, and size of reactors. “We are doing research on high-density fuels that don’t require as much enrichment, which means the reactor can be scaled down,” says Josh White, a senior scientist in the Lab’s Materials Science and Technology division. “Decreasing the amount of uranium needed in the reactor makes the reactors smaller and easier to build.”
One new fuel type under development is high-assay, low-enriched uranium (HALEU), which contains an increased concentration of uranium-235 (the fissile uranium isotope) to improve reactor performance, reduce refueling needs, and decrease waste volume. HALEU would allow researchers to design new types of reactors that can operate for decades without refueling and that produce less waste.
“Los Alamos National Laboratory is one of the few places in the country that can make that fuel,” says White, noting that HALEU is not commercially available in the United States. This is a problem because demonstration (prototype) reactors require hundreds of kilograms of fuel to achieve proof of performance.
To bridge the gap, the Low-Enriched Fuel Fabrication Facility (LEFFF) is being built at Los Alamos and is expected to be fully operational by 2025. LEFFF will start by fabricating HALEU for Kairos Power, a private company with a New Mexico facility that is making nuclear fuel pellets for a demonstration reactor under construction in Tennessee.
LEFFF will make a variety of different types of fuels, working with one customer at a time. “We will be a national tool to facilitate the maturation of fuels,” says LEFFF team leader Tim Coons. “LEFFF will serve as a launching pad for these advanced reactor companies to move to the commercial stage of reactor development.”
When fully operational, the LEFFF team will use automation and advanced technology to focus on quality, performance, safety, and cost of whatever type of fuel the new reactor designs require. “This facility is the catalyst to promote the next generation of advanced fuels coupled with advanced nuclear reactors,” Coons says. “If we are successful, you are going to start to see nuclear reactors used commercially throughout the United States.”
The spotlight on size
So, what will these advanced reactors look like? When it comes to nuclear reactors, bigger isn’t necessarily better. Los Alamos scientists are working with industry partners to develop small modular reactors and microreactors—diminutive, easy-to-produce, portable sources of nuclear energy.
“Our goal is to develop reactors that can be fully factory manufactured and deployed fast,” Rao says. These reactors can fit on a plane, train, or truck for quick and easy delivery to remote areas, such as isolated military bases or communities hit by natural disasters. Need more power? Add multiple reactors. They can be used in groups to produce low-carbon energy and can operate as part of the electric grid, independently from the electric grid, or as part of a microgrid, a self-sufficient energy system that can be connected or disconnected from the larger power grid.
Microreactors can produce between 0.1 and 20 megawatts of energy, whereas the smallest operating U.S. nuclear power plant produces 581 megawatts. To put that in perspective, a microreactor generating 10 megawatts of energy can produce around 10 years or more of electricity for more than 5,000 homes, 24 hours a day, 7 days a week.
Microreactors are self-contained within a single portable unit. Scientists say these tiny power generators are expected to operate for years without refueling or waste removal. “They are basically for places that are hard to get power to, such as mine sites,” White says. “You can put one up in the Arctic for 10 to 30 years and leave it alone.”
"Our goal is to develop reactors that can be fully factory manufactured and deployed fast.”
—Dasari V. Rao
Rao says the key to success is standardizing production of reactor components to speed up fabrication time and cut down on costs. He describes the technology as still in the growing stages and notes he is cautiously optimistic about the future. “I expect that microreactors will be pretty big game changers going forward,” he says. “But we need to be able to deploy them, have them operate somewhat autonomously, and have regulators feel comfortable about that.”
The materials matter
Another area Los Alamos scientists are working on is the development and testing of new materials for moderators and reactor construction. Moderators are any material placed in the reactor core to slow down neutrons and create more fissions. By experimenting with different types of moderators, Lab researchers are finding ways to make reactors safer. “The benefit of solid moderators is if the temperature gets too hot, the reactor will passively shut down without an operator,” White says. “Safety is dramatically enhanced without requiring the human part of the equation. It’s not possible for the reactors to fail. They are inherently engineered not to fail.”
One of the moderators Los Alamos scientists are developing is yttrium hydride—a rare earth metal and hydrogen mixture. “This moderator allows us to make smaller, more efficient microreactors that produce fewer waste products,” says Los Alamos nuclear engineer Holly Trellue.
Other materials research focuses on methods used for cooling, such as replacing water cooling with molten salt, and advanced materials to meet the unique demands of the smaller reactor designs.
“To be able to produce power efficiently in a microreactor,” Trellue explains, “we would like to be able to operate at as high a temperature as possible, so we are experimenting with different structural materials, advanced fabrication methods, and new approaches to shielding.”
She points out that one of Los Alamos’ key contributions to reactor advancements is the development of heat pipes that use passive cooling to make the reactors safer and more portable. “Los Alamos is the expert on heat pipe technology,” she says. “As a Lab we have always had great ideas, state-of-the-art facilities, and expertise to contribute to advanced reactor systems.”
The next step for nuclear
If it seems as though Los Alamos researchers are reaching high with their new reactor ideas, they are—including all the way to outer space. The Lab has supported research on nuclear propulsion technology and the possibility of using reactors to power human outposts on the Earth’s moon and Mars. In 2018, the Laboratory—in conjunction with the National Aeronautics and Space Administration and the Department of Energy—tested a system named KRUSTY (short for kilopower reactor using Stirling technology).
Development of new technology and collaborations to support both space and terrestrial applications will continue at the Lab. Trellue says she has many reasons to feel excited about this work, including “developing clean energy sources, helping remote communities meet their energy needs, being part of the nuclear growth of this country, and developing this energy source.”
Coons shares that commitment to continued nuclear research. “It’s an incredibly exciting time to be a part of this. I think nuclear is the future,” he says. “The demonstration reactors are part of reaching that—showing people these reactors are viable and safe.”
White agrees. “These are not your grandfather’s or great-grandfather’s reactors,” he says. “This is the next generation of nuclear energy and one of the best solutions for climate issues.”
As for Rao, he’s ready for action. “I want to build a microreactor before I retire. A really small, completely mobile reactor,” he says. “We have the ability to do that here at Los Alamos.” ★