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Lesson 5 of 9 · about 19 minutes

SMR and microreactor work at Idaho National Laboratory

You'll be able to

  • Describe INL's test beds for microreactors and what each will test
  • Give the dates of the 2026 criticality milestones at INL and say what zero-power criticality proves
  • Describe Oklo's, Aalo's and BWXT's projects at INL and the authority each runs under
  • Explain INL's role in HALEU supply and why the 1995 settlement agreement shapes it

Idaho National Laboratory has hosted 55 reactors since 1949, and the Idaho nuclear history lesson covers that story, from EBR-I's light bulbs to SL-1. This lesson stays in the present. In 2026 the desert west of Idaho Falls became the busiest place in the country for new reactor testing, and most of it involved small reactors built by private companies on a federal site.

Almost everything here runs under DOE authority, not an NRC license. That is the point of INL's role: companies can build and test on federal land under DOE safety rules, faster than a commercial license allows, and then take the data to the NRC.

The 2025 to 2028 timeline

2025202620272028 Aug: DOE names 10pilot companies Sept: Oklo Auroragroundbreaking June 4: Antares critical June: Aurora PDSA approved July 1 to 4: DeployableEnergy, Aalo critical July: Radiant fuel at DOME Oct 6: MARVEL vessel arrives MARVEL criticality;Deployable at DOME eVinci prototypeto DOME (2027 to 28) MARVEL full power;Pele first power target Dots in 2027 and 2028 are plans, not results.
Milestones reported by INL, DOE, ANS and the companies. Planned dates move often.

NRIC and the test beds

The National Reactor Innovation Center is a DOE program run out of INL. Its job, in its own words, is to find and fill the gaps that slow nuclear progress: test space, fuel handling, regulatory engagement. Its two named test beds are DOME and LOTUS. INL's public pages describe DOME in detail; LOTUS is listed as a second test bed, but details on its schedule were not confirmed for this lesson.

DOME, the Demonstration of Microreactor Experiments, is built around the containment structure of EBR-II, the sodium fast reactor that ran from 1964 to 1994. Reusing a containment that already exists saves years. DOME can host reactors up to 20 megawatts thermal fueled with HALEU.

  • Radiant Kaleidos goes first. Radiant received its TRISO fuel, made by Standard Nuclear in Oak Ridge, at DOME in July 2026, and the reactor itself left Radiant's California plant for INL in August. The plan is five phases: zero-power criticality, 1 MW thermal, full power, full heat, and at least 150 hours at full power without operator intervention. Radiant targeted finishing the campaign in the third quarter of 2026. No criticality announcement had been found for this lesson as of mid-October.
  • Westinghouse eVinci's 1 MWe prototype is slated for DOME in the 2027 to 2028 window, after a zero-power experiment on a scaled mock-up of its core in Nevada, reported in August 2026.
  • Deployable Energy was selected to test its nuclear battery at DOME in 2027.

MARVEL

MARVEL is DOE's own microreactor: about 85 kilowatts thermal and 10 kilowatts electric, cooled by sodium-potassium alloy moving by natural circulation at 500 to 550 °C, and housed in the TREAT facility at INL's Materials and Fuels Complex. It is about the size of a sedan. DOE approved the safety documentation for initial criticality on March 11, 2026, and on October 6, 2026 granted federal safety approval as the primary vessel arrived in Idaho. INL's schedule: installation in TREAT starting late 2026, initial criticality in 2027, full-power operation in 2028, process heat work likely in 2029.

Its purpose is to be a shared test platform. Companies that want to see how a microreactor works with a microgrid, a data center rack or an industrial heat user can plug in their equipment without building their own reactor.

The Reactor Pilot Program and the July 4 race

Executive Order 14301, signed May 23, 2025, told DOE to get at least three test reactors critical by July 4, 2026. In August 2025 DOE named 10 companies. Here is what happened, per ANS and Neutron Bytes:

CompanyReactorWhereMilestone
AntaresMark-0INLZero-power criticality June 4, 2026
Valar AtomicsWard 250Utah San Rafael Energy LabCriticality June 18, 2026
Deployable Energy (added to the program in April 2026)UnityINLZero-power criticality, announced July 1, 2026
Aalo AtomicsAalo-X critical test reactorINLCriticality July 4, 2026

These were zero-power tests. They show the core goes critical when and how the designers predicted. They do not show the reactor can run hot for years, survive a loss of cooling or make electricity at a price anyone will pay. Read headlines about "reactors switched on in Idaho" with that in mind.

Aalo, Oklo and Pele

Aalo Atomics had its documented safety analysis for the Aalo-X critical test reactor approved by DOE Idaho in spring 2026. On June 25, Energy Secretary Chris Wright said he had authorized Aalo to proceed with the 10 MWe Aalo-X at INL. Aalo's own timeline says Aalo-X will power a co-located data center in 2027 and inform its later "Aalo Pod" product in 2028. It announced a partnership with Crusoe, a data center developer, on July 30, 2026, without saying publicly whether it involves Aalo-X.

Oklo's Aurora-INL broke ground in September 2025. Under DOE's process it signed an agreement and won approval of its nuclear safety design agreement in March 2026, then its preliminary documented safety analysis in June 2026. The last step, approval of the final documented safety analysis, allows operation. Oklo has not announced an operating date. The NRC describes Aurora at up to 75 MWe. Aurora is modeled on EBR-II, and its first fuel is meant to come partly from HALEU recovered from EBR-II's used fuel.

Project Pele is a gas-cooled microreactor BWXT is building at INL for the military. BWXT delivered the full TRISO fuel core in late 2025, and first power is targeted as early as 2028, per POWER Magazine.

HALEU from Idaho's old fuel

Most advanced designs need HALEU, uranium enriched to between 5 and 20 percent U-235, and no domestic commercial supplier makes it at scale yet (lesson 8). INL holds one of the few existing sources: highly enriched uranium in used fuel from EBR-II and research reactors. DOE says INL aims to make up to 10 metric tons of HALEU available by recovering and downblending that material.

The Idaho settlement agreement shapes this work. The 2019 supplemental agreement between Idaho and DOE requires DOE to treat EBR-II driver fuel pins into HALEU at no less than 165 pounds a year on a three-year rolling average and to finish by December 31, 2028, with resulting waste other than high-level waste disposed of outside Idaho by January 1, 2035. Lesson 9 covers what the agreement means for spent fuel from the new reactors.

Example: how far Idaho's HALEU goes

  • INL's target: up to 10 metric tons.
  • DOE's estimate of domestic demand: up to 50 metric tons a year by 2035.
  • 10 ÷ 50 = 0.2 of one year, or about 2.4 months of 2035 demand.

So the EBR-II material is a bridge for first cores and demonstrations, like Aurora's. It cannot fuel a fleet. That is why the enrichment contracts in lesson 8 matter more over time than anything recovered in Idaho.

The project that didn't happen

The first commercial SMR planned at INL was the Carbon Free Power Project, six NuScale modules for Utah Associated Municipal Power Systems. It was cancelled in November 2023 when costs rose and subscribers withdrew (lesson 4). So in October 2026 INL is full of small test and demonstration reactors and has no commercial power plant under construction. Aurora, if it runs and sells power, would be the first.

Common mix-ups

  • Claim: Reactors turned on at INL in 2026 are now powering homes. What the evidence shows: The 2026 milestones were zero-power criticality tests. MARVEL is not scheduled to reach full power until 2028.
  • Claim: The NRC licensed the reactors at INL. What the evidence shows: Aalo, Antares, Deployable Energy, Radiant at DOME, Oklo's Aurora and MARVEL are DOE-authorized.
  • Claim: Idaho has plenty of HALEU for the new reactors. What the evidence shows: INL aims for up to 10 metric tons from old fuel, a fraction of one year of projected national demand.

Reporting angle

  • For each INL project, ask DOE Idaho for the safety documents approved so far (safety design strategy, PDSA, DSA) and the NEPA document covering it: categorical exclusion, environmental assessment or impact statement.
  • Ask where each reactor's spent fuel will go, and whether it counts against the 1995 settlement agreement's caps or the 2035 removal deadline. Lesson 9 explains why the answer isn't obvious.
  • Ask each company whether it plans to sell power from its INL unit, to whom, and whether that would need an NRC license.
  • Track Idaho DEQ's INL Oversight Program reports and the annual settlement agreement compliance updates.
  • When a company announces a data center partnership tied to an INL reactor, ask whether the data center will be on INL land, nearby or elsewhere, and who supplies backup power.

Research angle

Check yourself

1. INL's DOME test bed is built inside what?

2. Which company's reactor was first to reach DOE-authorized criticality at INL under the 2026 push?

3. What does a zero-power criticality test show?

4. As of October 2026, what was MARVEL's schedule?

5. Under the 2019 supplemental agreement with Idaho, by when must DOE finish treating EBR-II driver fuel into HALEU?

6. BWXT's Project Pele at INL is being built for which customer?

Terms in this lesson

NRIC
The National Reactor Innovation Center, a DOE program led by INL that gives private developers test beds and help moving designs toward demonstration.
DOME
Demonstration of Microreactor Experiments, an INL test bed in the old EBR-II containment for fueled microreactor tests up to 20 MWt.
Zero-power criticality
A self-sustaining chain reaction at a power level too low to make useful heat, used to confirm a core's physics.
Reactor Pilot Program
A DOE program created under Executive Order 14301 (May 2025) to authorize privately funded test reactors under DOE authority, with a goal of three reaching criticality by July 4, 2026.
Downblending
Mixing highly enriched uranium with lower-enriched uranium to make fuel below 20 percent U-235, such as HALEU.

Full glossary

Sources