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Courses › Supplemental Nuclear: Small Modular Reactors

Lesson 8 of 9 · about 17 minutes

Fuel types and the HALEU supply problem

You'll be able to

  • Match each SMR and microreactor design to its fuel form
  • Explain why most advanced designs need HALEU and what makes it scarce
  • Compare U.S. HALEU production to DOE's demand estimate with real numbers
  • Name the fuel fabrication plants being built and their schedules

Fuel is where a lot of SMR schedules quietly break. TerraPower's Natrium was delayed when its planned supply of high-assay low-enriched uranium, which had come from Russia, disappeared after the 2022 invasion of Ukraine. The fuel cycle lesson covers mining, enrichment, the Russian uranium ban and the basic HALEU arithmetic. This lesson sorts the fuel forms the new reactors use and puts numbers on the HALEU gap as of October 2026.

Fuel forms and who uses them

Fuel formEnrichmentWhat it looks likeUsed by
Uranium oxide pellets in metal tubesLEU, under 5%Ceramic pellets stacked in zirconium-alloy rods, bundled into assembliesNuScale (4.95%), BWRX-300, Holtec SMR-300; the whole existing fleet
Uranium oxide, other configurationsVariesCeramic fuel in a non-water reactorAalo (its Aalo-1 specification lists UO2 ceramic fuel)
Metallic fuelHALEUUranium alloy slugs in steel tubes, cooled by sodiumNatrium, Oklo Aurora; EBR-II before them
TRISO particles in pebbles or compactsHALEUKernels under 1 mm coated in carbon and silicon carbide, packed into pebbles a few centimeters across or into small cylindersX-energy Xe-100, Kairos Hermes, Radiant Kaleidos, BWXT Pele
Uranium zirconium hydrideHALEUTRIGA-type fuel rods long used in research reactorsDOE's MARVEL
Fuel saltVaries by designUranium dissolved in molten fluoride or chloride saltTerrestrial Energy IMSR, Natura MSR-1

The light-water SMRs have the easiest fuel story by far. They buy the same kind of fuel the existing fleet buys, from suppliers that already exist. That is a big reason TVA and Ontario picked the BWRX-300. Nearly everything else needs HALEU.

Why advanced designs want HALEU

DOE says most advanced reactor designs need HALEU so the reactors can be smaller, run longer between refuelings and operate more efficiently. More U-235 per kilogram means a small core can stay critical for years. For a microreactor meant to run sealed for a long stretch, or a fast reactor meant to burn its fuel deeply, that matters a great deal.

HALEU is enriched to between 5 and less than 20 percent U-235. Twenty percent is the international line where uranium becomes highly enriched, which is why designs stop at 19.75 percent. That line is now contested. In a June 2024 Science policy article, five proliferation experts led by R. Scott Kemp argued that HALEU above about 12 percent U-235 could be used directly in a practical weapon. They recommended keeping power reactor fuel below 10 to 12 percent, or else guarding higher-enriched HALEU like highly enriched uranium. The American Nuclear Society answered in a September 2024 open letter that it was unconvinced, that HALEU has fueled research reactors for over 60 years without known diversion, and that any change in the definition should be made internationally through the IAEA. For local purposes, the practical point is that HALEU fuel and shipments get tighter security than ordinary reactor fuel either way.

The supply problem in numbers

DOE's own HALEU program page says flatly that HALEU is not currently available from domestic suppliers. Here is what was on the table in 2026:

  • Centrus, Piketon, Ohio. Under a DOE demonstration contract, Centrus finished its final 900 kilograms of HALEU in mid-June 2026, two weeks early, for a cumulative total over the contract of more than 1,900 kilograms. In July 2026 it finalized a $900 million DOE task order to expand. Its initial build-out is 12 metric tons a year of capacity, with the first new commercial capacity expected online by 2029.
  • General Matter, Paducah, Kentucky. Also won a $900 million HALEU task order in January 2026; it has said it expects operations by 2034.
  • Recovered material at INL. DOE says INL aims to make up to 10 metric tons available from recovered and downblended uranium, including EBR-II fuel (lesson 5).
  • Demand. DOE estimates domestic HALEU demand could reach 50 metric tons a year by 2035.

Example: the HALEU gap

  • Everything Centrus made under the demonstration contract: about 1.9 metric tons.
  • Projected demand in 2035: 50 metric tons a year. 1.9 ÷ 50 = 0.038, under 4 percent of one year.
  • Centrus's planned 12 metric tons a year: 12 ÷ 50 = 24 percent of 2035 demand.
  • Add INL's one-time 10 metric tons, and the first years of new capacity still fall well short of 50 a year, unless General Matter, other enrichers or imports from allies fill the rest.

So for the rest of this decade HALEU is rationed. DOE runs an allocation process that decides which developers get the limited amounts, and every advanced reactor schedule should be read with the question: whose HALEU, and how much is actually allocated?

Making the fuel, not just the uranium

Enriched uranium is a gas, uranium hexafluoride. It has to be deconverted to metal or oxide, then fabricated into the fuel form. Each step needs licensed facilities, and several are being built now:

  • X-energy TX-1, Oak Ridge, Tennessee. Holds an NRC Part 70 fuel fabrication license. Vertical construction began September 2025; about 56 percent complete in June 2026; operations expected in the first half of 2028. A second plant with four times the capacity is planned on the same site.
  • Standard Nuclear, Oak Ridge. Made the TRISO fuel delivered to Radiant at INL in July 2026, and signed a fuel supply agreement with Antares in August 2026.
  • BWXT. Delivered the full TRISO core for Project Pele in late 2025.

TRISO is harder to make than pellets. A single reactor core holds a very large number of particles, and each coating layer has to be right, since the coatings are the first barrier holding fission products in. Quality control at that scale is something no U.S. plant has yet done commercially, which is part of why the fuel plants and the reactors come online on similar schedules.

What this means for a local project

Example: reading a fuel claim

An invented developer, Cutbank Energy, tells the county commission its HTGR "is fueled for 60 years."

  • Design life and fuel life are different things. The plant may be designed to operate for 60 years. TRISO pebbles cycle through and are replaced continuously, and microreactor cores are swapped every several years.
  • Ask: who supplies the HALEU, under what contract, and has DOE allocated any to this project?
  • Ask: which plant fabricates the fuel, is it licensed and operating, and when?

A confident "60 years of fuel" with no contract behind it tells you the presenters don't know the fuel chain. That is useful information too.

Common mix-ups

  • Claim: HALEU is weapons-grade. What the evidence shows: HALEU is below 20 percent U-235, the line for highly enriched uranium. Weapons use far higher enrichment. Security requirements are still stricter than for ordinary LEU.
  • Claim: The U.S. has plenty of enrichment, so fuel isn't a problem. What the evidence shows: DOE says no domestic commercial HALEU supply exists yet; new capacity is targeted for 2029 and later.
  • Claim: All SMRs need special fuel. What the evidence shows: Light-water SMRs use standard LEU. The HALEU problem hits the sodium, gas, salt and most microreactor designs.

Reporting angle

  • Ask every advanced reactor developer whether it has a DOE HALEU allocation, a commercial enrichment contract, or neither.
  • Ask which fabrication plant makes its fuel and whether that plant holds an NRC Part 70 license.
  • Ask how fresh fuel will be shipped to the site and under what security plan. HALEU shipments carry higher security categories than standard fuel.
  • Track DOE's HALEU allocation announcements and the Centrus and General Matter construction schedules; slips there predict slips at reactor sites.
  • Check company SEC filings for fuel risk disclosures, which are often franker than press releases.

Research angle

Check yourself

1. Which fuel form uses poppy-seed-sized uranium kernels coated in carbon and silicon carbide layers?

2. What enrichment range defines HALEU?

3. About how much HALEU had Centrus produced in total under its DOE demonstration contract by mid-June 2026?

4. DOE estimates domestic HALEU demand could reach about how much per year by 2035?

5. Which reactors in this course use standard low-enriched uranium, not HALEU?

6. When does X-energy expect its TX-1 TRISO fuel plant in Oak Ridge to begin operations?

Terms in this lesson

LEU
Low-enriched uranium, under 20 percent U-235. Commercial light-water reactor fuel is usually under 5 percent.
HALEU
High-assay low-enriched uranium, enriched between 5 percent and less than 20 percent U-235.
TRISO
Tri-structural isotropic fuel: tiny uranium kernels inside layers of carbon and silicon carbide that hold fission products at high temperature.
Metallic fuel
Uranium alloy (often with zirconium) in metal form, used in sodium fast reactors such as Natrium and EBR-II.
Fuel salt
A molten salt with uranium dissolved in it, so the fuel is liquid and also carries heat.
Deconversion
Turning enriched uranium hexafluoride gas back into a solid form, such as oxide or metal, so it can be made into fuel.

Full glossary

Sources