The 93 currently active nuclear-power reactors in the United States burn about 2,000 tonnes of uranium fuel each year. However, the type of uranium fuel those reactors use is not going to cut it for the advanced reactors expected to go on line in the coming years, as part of the effort to meet the country’s goal of 100 percent clean electricity by 2035. The specialized fuel these advanced reactors will need is currently made on a commercial scale only in Russia.
Not for long, though. Last week, Centrus Energy in Bethesda, Md., jump-started the first commercial domestic nuclear fuel production in the United States in 70 years by delivering the first load of high-assay, low-enriched uranium (HALEU) fuel made at its Piketon, Ohio, plant to the U.S. Department of Energy (DOE). The company is on track to produce 20 kilograms of HALEU by the end of the year, and then expects to produce 900 kg in 2024, says Jeffrey Cooper, director of engineering at Centrus.
This is a critical step toward large-scale deployment of advanced nuclear plants in the United States. The DOE expects to invest about US $600 million to mature next-generation reactors through its Advanced Reactor Demonstration Program, and “nine out of 10 of those reactors use HALEU fuels,” Cooper says.
“We’d like to avoid increasing our dependence on energy fuels from Russia. So it’s critically important that we secure our supply of HALEU material, given the number of advanced reactors desiring to use it in the future for commercialization.” —Kathryn Huff, Department of Energy
Less than one percent of natural uranium is U-235, the uranium isotope capable of sustaining a nuclear chain reaction. Today’s reactors use low-enriched uranium (LEU), which is almost 5 percent U-235. HALEU is enriched further to a concentration, or assay, of almost 20 percent U-235, which is still considered low-enriched comparedwith the 90-plus percent level that is required for weapons-grade uranium.
“The higher concentration of U-235 allows for higher power densities in the cores of advanced reactor designs,” Cooper says. That means more efficient reactors with smaller cores, longer core lives, and less fuel waste. The energy in just 3 tablespoons of HALEU can supply a lifetime’s worth of power for the average U.S. consumer, according to Centrus.
Research reactors at U.S. national laboratories and universities today use a small amount of HALEU provided by the DOE. There are three different ways to make HALEU. Gaseous diffusion—the “old-school way we used to do it,” according to Kathryn Huff, the assistant secretary for nuclear energy at the DOE, at federally owned enrichment facilities for the Manhattan Project and commercial nuclear sector for years—fell from favor because it is extremely energy intensive.
Centrus and the Russian state-owned company Tenex, which are the only two outfits that can produce HALEU in the world, use a method called gaseous centrifusion. Centrus starts with nearly 5 percent enriched uranium in gas form and spins it at very high speeds in four-story-tall tubular centrifuges, where the centrifugal forces separate the isotopes based on weight. “The U-238 is flung to the wall, and U-235 stays preferentially in the interior,” Cooper says. “We get two streams that come out—the product stream, which is enriched in U-235, and what we call the tail stream, which has less material.”
The gas is channeled through a cascade of centrifuges, where it gets progressively more enriched until reaching the target HALEU enrichment level of 19.75 percent. Centrus currently operates one cascade of 16 centrifuge machines.
Another promising enrichment technology, called laser enrichment, involves separating uranium isotopes based on the different energy levels at which their nuclei get excited. The technology is still in early stages of development, though, and Huff says that the DOE is closely watching Global Laser Enrichment in Wilmington, N.C., as a company that’s piloting the technology and that “could easily be a player in coming years.”
Not all next-generation reactors will use HALEU, Huff points out. Small modular reactors being developed by GE and Westinghouse, for instance, use water as a coolant and uranium oxide as fuel, and are “basically shrunken versions of conventional reactors in the [United States]. They want to use standard LEU fuel,” says Huff.
HALEU is needed instead for advanced reactors with more creative coolants and fuels, which are trying to achieve very compact core sizes. These include Bellevue, Wash.–based TerraPower’s sodium-cooled fast reactor, Rockville, M.D.–based X-energy’s high-temperature gas reactor, and Alameda, Calif.–based Kairos Power’s fluoride-salt-cooled high-temperature reactor.
The DOE projects that the United States will need more than 40 tonnes of HALEU before the end of the decade. But advanced reactor makers are still years away from firing up their cores. For instance, TerraPower (backed by Bill Gates) announced last December that it was delaying its Natrium reactor demonstration by two years because of a lack of HALEU fuel.
Centrus will have to build multiple cascades, each with 120 centrifuges, to make HALEU on a commercial scale. Right now, Centrus has an understanding in place with TerraPower, but not a formal purchase agreement.
Uranium enrichment supplier Urenco, which is co-owned by the British government, the Netherlands government, and German utilities, is also considering HALEU production at its New Mexico–based enrichment facilities, where it produces LEU today. Meanwhile, Lynchburg, Va.–based BWXT, which in August announced that it will be producing 2 metric tons of HALEU over the next five years for the National Nuclear Security Administration, is “prepared to make more HALEU for the U.S. government in the future in support of the advanced-reactor market,” says Sharon Smoot, president of BWXT’s nuclear fuels business unit. “Like any vendor, we look for market signals, and we’re optimistic about what we see.”
For now, the DOE intends to purchase about 25 tonnes of HALEU per year to kick-start the industry and give HALEU producers secure contracts from which they can expand production. “We’d like to avoid increasing our dependence on energy fuels from Russia,” Huff says. “So it’s critically important that we secure our supply of HALEU material, given the number of advanced reactors desiring to use it in the future for commercialization.”
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