# Are X-energy, BWXT, and Radiant Industries Testing New TRISO Fuel at INL?

Three [high-temperature, gas-cooled reactor](https://smrintel.com/glossary/htgr) developers — [X-energy](https://smrintel.com/companies/x-energy), [BWX Technologies](https://smrintel.com/companies/bwxt), and [Radiant Industries](https://smrintel.com/companies/radiant-industries) — are actively irradiating or preparing to irradiate novel TRISO fuel variants at Idaho National Laboratory's Advanced Test Reactor, with the explicit goal of qualifying fuel for three distinct commercial designs: X-energy's Xe-100, the BWXT Advanced Nuclear Reactor (BANR), and Radiant's Kaleidos microreactor. The fuel forms under test include uranium nitride kernels, pebble geometries, annular compacts, and other formulations — variants that go beyond the uranium oxycarbide (UCO) standard established under the Department of Energy's decade-long Advanced Gas Reactor (AGR) Fuel Development and Qualification Program. X-energy's fuel is already inside the ATR undergoing irradiation; BWXT and Radiant are in preparation. The strategic aim across all three programs is to push TRISO beyond its historical envelope — specifically toward higher power densities and longer refueling intervals — while retaining the inherent safety characteristics that make TRISO the preferred fuel for advanced gas-cooled designs. INL's ATR, rated at 250 MW thermal, remains the world's primary facility for accelerated nuclear fuel and materials testing, offering nine large flux traps and 68 drop-in positions to run multiple industry experiments simultaneously during each 60-day operating cycle.

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## Why TRISO Fuel Variants Matter Now

Standard TRISO particles — poppy seed–sized spheres of [high-assay low-enriched uranium](https://smrintel.com/glossary/haleu) (enriched above 5% but below 20% U-235) wrapped in multiple ceramic and carbon layers — have been studied for decades and have a proven irradiation record stretching back to Fort St. Vrain's first commercial use of TRISO in 1979. The fuel's silicon carbide and carbon coatings contain fission products at temperatures well above the melting point of steel, a property that underpins passive safety claims for every HTGR design currently seeking NRC licensing.

But standard UCO TRISO compacts have limits. As INL experiment design engineer Joe Palmer told ANS News, conventional light water reactor fuels begin releasing fission products when the fuel melts; TRISO's ceramic layers maintain containment at "extraordinarily high temperatures — much higher than the melting point of steel." That advantage is well-established. What the current industry-INL collaboration is probing is whether alternative kernel chemistries and fuel geometries can extend [fuel burnup](https://smrintel.com/glossary/burnup), raise power density, or improve manufacturability without compromising that containment integrity.

Uranium nitride (UN) kernels, for instance, offer higher uranium density than UCO, which could translate directly to longer core life or higher specific power — both commercially valuable for designs like the Kaleidos, which targets mobile and off-grid deployment where refueling logistics are a cost driver. Annular and pebble form factors address different reactor architectures: pebbles suit X-energy's Xe-100 pebble-bed design, while annular compacts may offer manufacturing or neutronics advantages for prismatic core designs like BANR.

Whether these variants perform as modeled under real irradiation conditions is the open question the ATR program is designed to answer. Postirradiation examination — the destructive and non-destructive analysis of irradiated samples — will ultimately determine whether any variant clears the qualification bar.

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## The AGR Program: What the Industry Inherited

The current testing builds directly on work that began in 2002, when [BWX Technologies](https://smrintel.com/companies/bwxt), the DOE, INL, and Oak Ridge National Laboratory launched the AGR Fuel Development and Qualification Program alongside the Next Generation Nuclear Plant initiative.

The first AGR irradiation used a split manufacturing process: BWXT produced UCO kernels, ORNL applied the TRISO coatings and compacted the particles into cylindrical fuel forms, and INL irradiated them in the ATR. Over the following decade, the collaboration advanced from laboratory-scale fabrication to full production-scale manufacturing, with BWXT eventually handling the complete process — kernel production, TRISO coating application, and compact fabrication.

"The postirradiation examination of those fuels showed that the scaled-up fuel form performs well, compared to the smaller lab-scale produced fuel," said John Stempien, who served as INL's technical lead for AGR postirradiation examination.

That scale-up validation was not trivial. TRISO fabrication is a precision process, and particle-to-particle coating uniformity is critical to the fuel's fission product retention performance. The AGR program demonstrated that industrial-scale production could replicate lab-scale quality — a prerequisite for any commercial HTGR supply chain.

The DOD's Project Pele program, issued in 2019 and awarded to BWXT, added further impetus: BWXT began expanding its TRISO manufacturing line capacity specifically to support that portable military reactor program, giving the company additional throughput to apply to commercial qualification campaigns.

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## Three Reactors, Three Qualification Paths

The current INL collaboration is qualifying TRISO fuel for three distinct reactor programs, each with different power output, market target, and regulatory trajectory:

**X-energy Xe-100:** A pebble-bed HTGR design. X-energy's fuel is the furthest along in the current campaign — already inside the ATR for irradiation. The Xe-100 has been one of the DOE's [Advanced Reactor Demonstration Program](https://smrintel.com/glossary/ardp) selections, giving it significant federal support for both reactor development and fuel qualification.

**BWXT Advanced Nuclear Reactor (BANR):** A prismatic HTGR design from BWX Technologies. BWXT's irradiation preparations — visible in CT images showing TRISO particle kernels within test compact preforms — suggest the company is testing compact geometries, potentially including annular forms, that differ from the cylindrical AGR standard.

**Radiant Kaleidos:** A microreactor design from [Radiant Industries](https://smrintel.com/companies/radiant-industries) targeting mobile and off-grid applications. Radiant's preparation for ATR irradiation signals that the company is moving from design-phase fuel specification into active experimental qualification — a meaningful program maturity milestone.

Each qualification path requires irradiation data to support NRC licensing submissions. Fuel qualification is not a formality; it is one of the longest-lead items in any advanced reactor program, often running in parallel with reactor design certification on a multi-year timeline.

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## Analytical View: What the Industry Should Watch

The shift from a single government-funded qualification program (AGR) to multiple parallel industry-driven campaigns at the ATR reflects a maturing HTGR sector — but it also surfaces several pressure points worth tracking.

**HALEU supply chain remains the upstream constraint.** All three designs require uranium enriched above 5% U-235. Scaling from irradiation test quantities to commercial fuel loads requires a reliable enrichment and fabrication supply chain that does not yet exist at commercial scale in the United States. Fuel qualification data from the ATR is necessary but not sufficient; supply chain development runs on a separate, slower timeline.

**Postirradiation examination capacity is finite.** INL's ATR has 68 drop-in positions, but the hot cells and analytical infrastructure needed to examine irradiated fuel after it comes out of the reactor are a shared national resource. As more industry programs run simultaneously, scheduling and throughput for postirradiation examination — the step that actually generates the qualification data — could become a bottleneck.

**Manufacturing scale remains unproven for novel variants.** The AGR program demonstrated that production-scale UCO TRISO performs comparably to lab-scale material. That validation work has not been done for uranium nitride kernels or novel compact geometries. If irradiation results are favorable, the industry will face a second qualification challenge: proving that scaled-up manufacturing of these new variants replicates the test sample performance.

For utility procurement teams and energy investors evaluating HTGR commitments, the ATR irradiation campaigns are a leading indicator of program seriousness — companies willing to invest in fuel qualification are demonstrating commercial intent beyond press releases. But the gap between promising irradiation results and a licensed, fueled commercial reactor remains measured in years and in hundreds of millions of dollars.

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## Key Takeaways

- **X-energy's TRISO fuel is actively being irradiated** in INL's Advanced Test Reactor; BWX Technologies and Radiant Industries are preparing to irradiate their own fuel variants.
- **Three HTGR designs are targeted** for qualification: X-energy's Xe-100, BWXT's BANR, and Radiant's Kaleidos microreactor.
- **Novel fuel forms under test** include uranium nitride kernels, pebble geometries, and annular compacts — variants intended to enable higher power density or longer refueling cycles relative to standard UCO TRISO.
- **INL's ATR** operates at 250 MWth with nine large flux traps and 68 drop-in positions, enabling accelerated irradiation testing across multiple simultaneous industry campaigns.
- **The AGR program (2002–ongoing)** established the UCO TRISO baseline and demonstrated production-scale fabrication quality, providing the foundation these new campaigns build upon.
- **HALEU supply chain and postirradiation examination capacity** are the two systemic constraints that qualification data alone cannot resolve.

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## Frequently Asked Questions

**What is TRISO fuel and why do SMR developers prefer it?**
TRISO (tristructural isotropic) fuel consists of uranium particles individually encapsulated in multiple ceramic and carbon layers, including a silicon carbide barrier. The coatings contain fission products at temperatures well above the melting point of steel, providing passive safety characteristics that eliminate the need for active cooling systems to prevent fuel failure during accident conditions. This makes TRISO particularly attractive for high-temperature, gas-cooled reactor designs that rely on passive safety for their licensing basis.

**What fuel variants are X-energy, BWXT, and Radiant testing at INL?**
According to ANS News reporting on the INL collaboration, the variants under test include uranium nitride fuel kernels, pebble fuel forms, annular fuel forms, and other formulations. Standard TRISO uses uranium oxycarbide (UCO) kernels; uranium nitride offers higher uranium density, which could support higher power densities or longer refueling intervals.

**What is INL's Advanced Test Reactor and why is it used for fuel qualification?**
The ATR is a 250 MWth research reactor at Idaho National Laboratory. It provides nine large flux traps and 68 drop-in positions within the core and reflector, enabling high-neutron-flux irradiation of fuel and materials samples at accelerated rates. Decades of irradiation data from fuel tests at the ATR are accepted by the NRC as part of fuel qualification submissions.

**How does TRISO fuel qualification support NRC licensing for HTGRs?**
Fuel qualification requires demonstrating, through irradiation and postirradiation examination, that a fuel form retains its fission product containment performance across the full range of temperatures, burnup levels, and transient conditions it will experience in a commercial reactor. That data forms a core component of the safety analysis submitted to the NRC as part of a design certification or combined license application.

**When did commercial use of TRISO fuel begin?**
The Fort St. Vrain nuclear power plant in Colorado used TRISO fuel in a commercial reactor for the first time in 1979, according to the ANS News report. Modern TRISO qualification efforts build on more than four decades of operational and experimental data, including the DOE's Advanced Gas Reactor program that began in 2002.