Aalo Atomics Completes First Nuclear Reactor Built on DOE Land in 50 Years, Targeting Criticality Within Weeks
Austin-based Aalo Atomics unveiled its completed Critical Test Reactor at Idaho National Laboratory on March 20, built in just 36 days, as the startup races to achieve criticality ahead of the DOE's July 4 deadline.
Overview
Aalo Atomics, an Austin, Texas-based nuclear startup founded in 2023, unveiled its completed Critical Test Reactor at Idaho National Laboratory on March 20, 2026 — the first new nuclear reactor constructed on Department of Energy land in half a century. The facility was built in 36 days and the reactor assembled in 40 days, a construction pace that contrasts sharply with the decade-long timelines typical of conventional nuclear projects.
The company is now awaiting final DOE approval and fuel delivery before attempting to achieve zero-power criticality, which it expects to reach “well before” the July 4, 2026 deadline set by President Trump’s Nuclear Reactor Pilot Program. If successful, Aalo would become one of the first companies to hit criticality under the executive order initiative, which aims for at least three test reactors to go critical by Independence Day.
As previously reported, the DOE’s Reactor Pilot Program has been accelerating advanced reactor testing across multiple companies, with Valar Atomics achieving zero-power criticality at Los Alamos in November 2025.
What We Know
The Critical Test Reactor is a zero-power criticality reactor designed to validate the core physics and control systems of Aalo’s larger Aalo-X design — a 10-megawatt-electric sodium-cooled experimental reactor. The test reactor uses low-enriched uranium dioxide fuel at 5 percent enrichment, a graphite moderator for thermal neutron spectrum, and in-house developed control and shim rods, according to reporting based on the company’s technical disclosures.
Aalo was selected in August 2025 as one of 11 advanced reactor projects for the DOE’s Nuclear Reactor Pilot Program and broke ground at Idaho National Laboratory two weeks later. The Department of Energy identified land adjacent to INL’s Materials and Fuels Complex as the site for the facility, noting that the reactor is “inspired by DOE’s MARVEL microreactor design” and is intended to gather data on advanced safety systems, fuel performance, and coolant efficiency.
In December 2025, the company shipped five reactor test modules from its Austin pilot factory to INL, with CEO Matt Loszak stating that the shipment was “the beginning of something that will become routine within a few years, at 1000x the scale,” according to Interesting Engineering.
The fuel supply chain is now in place. On March 3, 2026, the company signed a fuel fabrication contract with Global Nuclear Fuel, a GE Vernova and Hitachi-led alliance, to secure fabricated fuel rods for the Aalo-X reactor, according to BusinessWire. Urenco USA completed uranium hexafluoride enrichment and delivered the material to GE Vernova for fabrication on March 10. The following day, the DOE approved Aalo’s Preliminary Documented Safety Analysis.
On March 4, Aalo selected Baker Hughes to supply a 10-megawatt steam turbine generator set for the Aalo-X reactor, with delivery expected by the end of 2026, according to BusinessWire.
The XMR Design
Aalo’s reactor occupies a new category the company calls an “extra-modular reactor” or XMR, positioned between microreactors (under 10 megawatts) and larger small modular reactors (100 to 300 megawatts). The design uses liquid sodium metal as its primary coolant, which the company says is approximately 100 times more effective at heat removal than water and allows the reactor to operate at atmospheric pressure, according to Interesting Engineering. This eliminates the need for massive containment domes and enables factory-built modules to be shipped as containerized units.
The commercial product, called the Aalo Pod, would combine five Aalo-1 reactors sharing a single turbine to deliver 50 megawatts of electricity — enough to power a mid-sized data center. The system is designed to operate without external water sources using air-cooled condensers, making it suitable for arid regions where traditional water-cooled plants cannot be built.
Yasir Arafat, Aalo’s co-founder and chief technology officer, has described the Aalo-X as a “proving ground — a chance to show how advanced nuclear can be safe, scalable, and cost-effective,” according to the Department of Energy.
What We Don’t Know
The Critical Test Reactor is a zero-power device, meaning it will sustain a controlled nuclear chain reaction at negligible energy output to validate physics models — not generate electricity. The path from zero-power criticality to a fully operational power-producing reactor involves separate construction of the full Aalo-X facility, which the company projects completing by the end of 2026. Full-power operation would follow after additional licensing and testing.
Aalo’s commercial timeline is ambitious. The company plans to submit its first commercial NRC license application in 2026, launch a one-million-square-foot “GigaWatt Factory” by 2028 capable of producing over a hundred reactors per year, and reach one gigawatt of operational capacity by the end of the decade. Whether a startup founded in 2023 with $136 million in total disclosed funding can achieve manufacturing at this scale within that timeframe remains an open question.
The broader Reactor Pilot Program faces its own uncertainties. Of the 11 selected projects, only Valar Atomics has achieved criticality so far. Whether three reactors will reach the July 4 target — and whether zero-power criticality experiments will translate into commercially viable power plants — will be closely watched indicators for the advanced nuclear sector’s prospects.