HALEU fuel: supply chain, safety, and the case for TRISO microreactors
High-Assay Low-Enriched Uranium (HALEU) is the fuel that unlocks the next generation of advanced reactors — including factory-sealed microreactors like TidalCore. This guide explains what HALEU is, why TRISO particle fuel is uniquely robust, where the U.S. supply chain stands in 2026, and how a 12-year sealed core becomes physically possible.
1. What HALEU is (and isn't)
HALEU is uranium enriched to between 5% and 20% U-235. Conventional light-water reactors (LWRs) operate on Low-Enriched Uranium (LEU) at roughly 3–5% U-235. Weapons-usable High-Enriched Uranium (HEU) begins at 20%. HALEU sits intentionally below that threshold — high enough to shrink cores and extend burnup, low enough to remain a non-proliferation-compliant commercial fuel.
| Fuel class | U-235 enrichment | Typical use |
|---|---|---|
| Natural U | 0.71% | CANDU heavy-water reactors |
| LEU | 3–5% | Today's commercial LWRs |
| HALEU | 5–20% | Advanced SMRs, microreactors, TRISO fuels |
| HEU | ≥ 20% | Naval propulsion, research reactors (being phased out) |
2. TRISO particles — the inherent safety case
TRISO (TRi-structural ISOtropic) is the fuel form most advanced microreactor designs pair with HALEU. Each particle is roughly the size of a poppy seed and contains four engineered layers around a uranium oxycarbide kernel:
- Porous carbon buffer — accommodates fission gas swelling
- Inner pyrolytic carbon (IPyC) — gas-tight inner barrier
- Silicon carbide (SiC) — the structural pressure vessel
- Outer pyrolytic carbon (OPyC) — mechanical protection
The SiC layer behaves as an individual ceramic pressure vessel. DOE and Idaho National Laboratory irradiation testing (AGR-1 through AGR-5/6/7) has demonstrated that TRISO particles retain fission products to peak fuel temperatures of ≥ 1,600 °C — well above the credible accident envelope of a passively cooled microreactor. The U.S. Department of Energy has publicly called TRISO "the most robust nuclear fuel on Earth."
The implication is decisive: a meltdown in the LWR sense — molten fuel breaching a pressure boundary — is not a physically credible failure mode for a TRISO-fueled microreactor. The fuel itself is the containment.
3. U.S. HALEU supply chain in 2026
For two decades the only commercial HALEU on the planet was Russian. That dependency is being unwound through a coordinated U.S. effort:
- Centrus Energy — American Centrifuge Plant, Piketon OH: the first U.S. HALEU production began in October 2023 under DOE contract. Phase 2 expansion is underway.
- DOE HALEU Availability Program: congressionally authorized to acquire HALEU and allocate it to advanced reactor developers via competitive solicitation.
- Prohibiting Russian Uranium Imports Act (2024):statutory ban on Russian enriched uranium with phased waivers through 2028, paired with $2.7 B in Inflation Reduction Act appropriations to scale domestic enrichment.
- Deconversion & fuel fabrication: BWXT, X-energy, and Orano are scaling UF₆-to-oxide deconversion plus TRISO fabrication capacity in Tennessee and Oak Ridge.
First-of-a-kind (FOAK) microreactor projects are expected to load DOE-allocated HALEU for initial cores while commercial enrichment ramps to NOAK volumes.
4. Why HALEU enables 12-year microreactor cores
Higher enrichment means more fissile atoms per kilogram of fuel. For a fixed thermal power, that allows the designer to choose any combination of three benefits:
- A physically smaller core (transportable as a sealed cassette)
- A longer interval between refueling (years instead of months)
- Higher achievable burnup (better fuel utilization)
Combined with TRISO's tolerance for high burnup, this is what makes a sealed 8–20 year core physically possible. Without HALEU, a microreactor of comparable output would need a larger core, on-site refueling infrastructure, and a much shorter cycle — eroding the economic case for unmanned remote deployment.
5. HALEU TRISO inside TidalCore
TidalCore is a 15 MWth / 5 MWe heat-pipe microreactor for port shore-power and green-ammonia bunker fuel synthesis. The fuel design choices flow directly from the maritime deployment context:
- Fuel form: HALEU TRISO pebbles in a graphite monolith, enriched to 19.75% U-235.
- Refueling interval: 12-year sealed cassette; the entire cartridge is shipped back to a central facility — there is no on-site refueling, no spent-fuel pool at the port.
- Primary coolant: liquid-metal heat pipes (no pumps, no large coolant inventory) deliver 850 °C process heat to a sCO₂ Brayton cycle and an ammonia-synthesis takeoff.
- Inherent safety: TRISO containment plus heat-pipe passive decay heat removal means no operator action and no AC power are required to reach a safe state — relevant for an urban port environment.
See the full concept and schematic and the specifications page for plant-level numbers.
6. NRC licensing posture for TRISO fuel
TRISO fuel has decades of operational pedigree — Fort St. Vrain, Peach Bottom Unit 1, and the German AVR and THTR — plus modern data from the DOE Advanced Gas Reactor (AGR) program. The NRC has issued a Safety Evaluation Report (SER) on Kairos Power's KP-FHR TRISO design, accepted topical reports from X-energy on Xe-100 fuel, and published the Topical Report on TRISO fuel qualification.
Under the new 10 CFR Part 53 risk-informed framework, the inherent containment provided by TRISO directly supports a smaller emergency planning zone and a streamlined safety case — both essential for siting near a populated port.
7. FAQ
- Is HALEU weapons-usable?
- No. The 20% U-235 ceiling is the international threshold separating HALEU from HEU. Weapons designs use enrichments far above that — typically > 90%. HALEU is a commercial reactor fuel under IAEA safeguards.
- Can existing LWRs burn HALEU?
- Not as designed. HALEU is purpose-made for advanced reactor cores (TRISO pebble beds, fast spectrum metallic fuels, molten-salt systems). Some accident-tolerant LWR fuel concepts use enrichments up to ~8%, the bottom of the HALEU range.
- What happens to a TidalCore cassette at end-of-life?
- The sealed cassette is shipped back to a central licensed facility for interim storage, eventual recycling, or geologic disposal — no on-site spent fuel handling at the port.