What Fuel Do SMRs Use? A Reactor-by-Reactor Comparison
60-second answer: There is no such thing as generic "SMR fuel." Small light-water designs like GE Vernova's BWRX-300 and NuScale's US460 run on the same sub-5% enriched uranium as today's fleet, fabricated on existing production lines. Most non-water-cooled designs specify HALEU (5–20% U-235) in forms the existing supply chain does not make: X-energy's Xe-100 uses TRISO pebbles at about 15.5% enrichment, TerraPower's Natrium uses HALEU metal, and Kairos runs TRISO pebbles in molten salt at up to 19.55%. The table below compares eight named designs on the five attributes that decide their uranium supply-chain exposure, each row tied to a developer or regulator source.
Stock guides sort these companies by investability and project trackers sort them by milestones. Neither answers the question that connects a reactor design to the uranium market: what exactly does it load, and who can make that?
The five fuel attributes that matter
Size, coolant, neutron spectrum, enrichment and fuel form are separate attributes, and each one maps to a different part of the supply chain:
- Enrichment assay decides whether the design can buy from today's LEU enrichers or joins the queue for scarce HALEU supply.
- Fuel form (oxide pellets, TRISO particles, metal, salt-dissolved) decides which fabrication plants can serve it, and whether such a plant exists yet.
- Coolant (water, helium, sodium, fluoride salt) shapes the fuel's operating environment but does not by itself set the assay; a salt-cooled reactor is not automatically a liquid-fuel or thorium reactor.
- Neutron spectrum (thermal vs fast) drives core inventory and what recycled material the design could eventually accept.
- Refueling approach (batch outages, online pebble circulation, whole-core replacement) sets the timing of fuel purchases.
The NRC's advanced-reactor category includes light-water designs alongside the exotic ones (NRC overview); "advanced" is a regulatory grouping, not a fuel specification.
Eight named designs, compared
Figures are the developers' or regulators' own; "n.p.s." means not publicly specified in a source we can cite. Verified September 17, 2026.
| Design (developer) | Output | Coolant | Fuel form | Specified assay | Fabrication source | Refueling |
|---|---|---|---|---|---|---|
| BWRX-300 (GE Vernova Hitachi) | 300 MWe | Water (BWR) | Conventional oxide assemblies | LEU, sub-5% | GE Vernova's established BWR fuel line (GEV) | Batch outages |
| US460 / VOYGR (NuScale) | 77 MWe per module | Water (PWR) | NuFUEL-HTP2 oxide assemblies | LEU, under 5% | Framatome, Richland WA; qualification notice incl. 444 assemblies for the first US customer (NuScale, Mar 2026) | Up to 24-month cycles |
| Xe-100 (X-energy) | 80 MWe / 200 MWth | Helium | TRISO pebbles | HALEU, ~15.5% | TRISO-X, Oak Ridge TN; HALEU from Centrus under an Aug 2026 agreement (X-energy) | Online pebble circulation (X-energy) |
| Natrium (TerraPower) | 345 MWe | Sodium (fast) | HALEU metal fuel pins | HALEU | Framatome metallization (Richland WA) + Global Nuclear Fuel assembly (Wilmington NC) (WNN) | Batch; first core ~15–20 tU HALEU |
| Hermes / KP-FHR (Kairos Power) | Hermes 1: 35 MWth demo; commercial KP-FHR ~150 MWe | FLiBe fluoride salt | TRISO pebbles (solid fuel in salt coolant) | HALEU, up to 19.55% (NRC environmental report) | In-house pilot line; BWXT teaming for commercial TRISO (WNN, Sep 2025) | Online pebble circulation |
| Aurora (Oklo) | 75 MWe (scaled from 15 and 50 MWe versions) | Sodium (fast) | HALEU metal | HALEU, up to 19.75% | Own Aurora Fuel Fabrication Facility at INL, using DOE-granted EBR-II material (DOE) | Multi-year cores; design target 10+ years |
| IMSR400 (Terrestrial Energy) | 2 × 195 MWe | Fuel dissolved in fluoride salt | Liquid fuel: UF₄ in salt | Standard-assay LEU, up to 5% (Power) | Fuel-salt supply via Orano/Centrus agreements; pilot plant contracted (WNN) | Replaceable core units |
| eVinci (Westinghouse) | 5 MWe / ~13 MWth | Sodium heat pipes | TRISO in a steel monolith | HALEU, 19.75% | n.p.s. | Whole-core replacement, 8+ year target (Power) |
Read the output column carefully: MWe and MWth are different numbers, and microreactor marketing often quotes the larger thermal figure. The eVinci is a 5 MWe machine; its DOE-class thermal rating is roughly 13 MWth.
Which designs need HALEU, and which do not
The dividing line runs between water-cooled and everything else, with one liquid-fuel exception:
- No HALEU needed: BWRX-300, US460 and the IMSR400 all run at or below 5% enrichment. The two light-water designs buy fuel from production lines that already exist (GE Vernova's BWR line, Framatome's Richland plant), which is a real schedule advantage: their fuel risk is commercial, not developmental. The IMSR is the outlier that pairs exotic engineering with standard-assay fuel.
- HALEU required: Xe-100 (~15.5%), Natrium, Aurora and eVinci (19.75%), and Kairos (up to 19.55%). Every one of these joins the supply queue documented in our HALEU guide, and several also need fabrication plants that are still under construction. TerraPower has publicly attributed its demonstration plant's schedule slip to HALEU availability (WNN).
Salt coolant is not salt fuel
Two designs in the table use molten fluoride salt, and they use it in opposite ways. Kairos pumps FLiBe salt as a coolant around solid TRISO pebbles; the fuel could be unloaded and handled as discrete objects. Terrestrial Energy dissolves uranium tetrafluoride into the salt itself, so the fuel is a liquid and the "fuel assembly" concept disappears entirely, replaced by sealed core units swapped on a schedule. The distinction matters for the supply chain: Kairos needs a TRISO pebble plant, Terrestrial needs a fuel-salt synthesis plant, and neither can use the other's. Neither design uses thorium; molten-salt cooling and thorium fuel are historically associated but independent choices.
Core inventory, reload interval and burnup
Refueling approach changes when uranium is bought more than how much. Three patterns appear in the table:
- Batch refueling (BWRX-300, US460, Natrium): outage-based reloads on 12–24 month cycles, like the existing fleet.
- Online refueling (Xe-100, Kairos): pebbles circulate continuously, so fuel demand is a steadier flow and startup inventories can be modest. Kairos's Hermes application put its required startup fissile inventory at no more than 25 kg of U-235 (NRC ER).
- Long-life cores (Aurora, eVinci): most or all of the uranium is bought up front, then nothing for years. Oklo's design targets a decade or more per core; eVinci targets eight-plus years per unit. These front-load procurement the way first cores do for large reactors, a dynamic covered in our reactor-fuel guide.
Per-design core masses are mostly not disclosed; where a developer has put a number in public (TerraPower's 15–20 tU first core), the table cites it, and where not, the honest entry is none.
Translating the table into supply-chain exposure
For uranium investors the table sorts projects into three exposure buckets. Designs on conventional LEU add demand through the existing mine-conversion-enrichment-fabrication chain the moment they order fuel, with no new facilities required. HALEU designs add demand that cannot be served until specific plants (Centrus's expansion, General Matter's Paducah project, TRISO-X, Standard Nuclear's lines) come online, so their fuel demand arrives only as fast as the slowest required facility. Liquid-fuel designs need dedicated fuel-salt production that exists today only as contracted pilot plants.
The reactor tracker follows which projects are advancing; the fuel-cycle equities page lists the companies on the supply side. A reactor order benefits a specific fuel chain, and this table says which one.
Frequently asked questions
What fuel do SMRs use? It depends on the design. Light-water SMRs (BWRX-300, NuScale US460) use the same sub-5% enriched oxide fuel as today's reactors. Most non-water-cooled designs use HALEU (5–20% U-235) in design-specific forms: TRISO particles for gas- and salt-cooled reactors, metal fuel for sodium fast reactors, or uranium dissolved in salt for liquid-fuel designs.
Which SMRs need HALEU? In this comparison: X-energy's Xe-100 (~15.5%), TerraPower's Natrium, Kairos's KP-FHR (up to 19.55%), Oklo's Aurora and Westinghouse's eVinci (19.75%). The BWRX-300, NuScale's US460 and Terrestrial Energy's IMSR do not; they run at or below 5% enrichment.
Is TRISO fuel the same as HALEU? No. TRISO describes the fuel form (ceramic-coated particles); HALEU describes the enrichment level. Current US TRISO reactor designs happen to specify HALEU kernels, but the terms answer different questions, and TRISO could in principle be made at other assays.
Do molten salt reactors use thorium? Not the ones in this comparison. Kairos uses salt only as coolant around solid uranium TRISO pebbles, and Terrestrial Energy dissolves standard-assay uranium fuel in its salt. Thorium is a separate fuel choice that no near-term US commercial design specifies.
Why does the fuel type matter for uranium demand? Because it sets which supply chain the reactor draws on and when. LEU designs can order fuel from existing plants today; HALEU designs depend on enrichment and fabrication capacity that is still being built, so their uranium demand arrives on the schedule of the slowest required fuel facility.
This article is for informational purposes only, not investment advice.