Antares Nuclear achieves first US reactor criticality in decades — a month ahead of the July 4 presidential deadline

Antares Nuclear lights up the first new US non-light-water reactor in roughly 40 years

Antares achieved first criticality on its micro nuclear reactor at Idaho National Laboratory last week, becoming the 53rd reactor at the national lab and the first new non-light-water reactor design commissioned on US soil in approximately 40 years. The milestone came a month ahead of the presidential July 4 deadline, which called for three reactors to be turned on in the US by America's 250th birthday.

Jordan Bramble, CEO and co-founder of Antares, describes the reactor as a heat-pipe-cooled micro system operating at near-atmospheric pressure, using small amounts of sodium that vaporize and condense passively to cool the core. The design targets the 100 kilowatt to 1 megawatt range, with units stackable for larger loads. The test at INL did not produce electricity — that milestone is targeted for 2027, with customer deployments planned for 2028. Bramble's shorthand: neutrons in '26, electrons in '27, dollars in '28.

Why non-light-water

The core engineering logic is temperature and location. High-temperature operation improves thermal efficiency, but pressurizing water to prevent boiling at those temperatures creates materials challenges and safety complexity. Without pressurization, a loss-of-coolant event doesn't risk vaporized radioactive material traveling large distances — a meaningful safety argument for remote or contested environments. The design also sidesteps the water access constraint entirely, which matters for desert, remote industrial, and eventually space applications.

“The president signed executive orders trying to speed up nuclear — one provision called for three reactors to be turned on on American soil by America's 200th birthday, July 4. We just turned on the first, a month ahead of schedule. This is the first privately-built non-light-water-cooled reactor in about forty years. We have an agreement with the Air Force to do several megawatts of power for Joint Base San Antonio in Texas.”

Standing on prior work

Antares didn't start from scratch. The fuel — TRISO fuel — was qualified through roughly 20 years of DOE-funded work under the Advanced Gas Reactor Program, with the specific supply chain built out by the Department of Defense under Project Pele. That existing qualification data let Antares point regulators to established fuel performance under high temperatures, reducing the safety analysis burden and allowing the deletion of redundant safety systems.

The regulatory path itself ran through DOE authorization rather than the NRC, streamlined by lessons from Project Pele. One INL operations representative in the joint test group had known the DOE regulators since 1979 — this was the first reactor they'd worked on together since before that year.

Bramble says the design work was hard, the regulatory process comparatively manageable when safety is integrated into engineering from the start, and the hardest part was the final two weeks of operating an actual nuclear facility. A real integration challenge surfaced during commissioning: actuator motors controlling the boron carbide rotating drums used for reactivity control were generating electromagnetic interference with the neutron detectors, requiring a five-to-six-day troubleshooting process before the team could proceed.

Why the military first

Antares has announced an agreement with the Air Force to deliver several megawatts of power to Joint Base San Antonio, Texas, with more military installation agreements expected by end of year.

The commercial logic is straightforward. The Army alone has a $2 billion budget under its JANIS program to purchase micro reactors for installations, with spending committed between now and 2029–2030. Data centers and hyperscalers are signaling interest through MOUs and small equity investments, but Bramble says they won't commit serious capital until the technology is operationally proven. The military will.

Beyond budget, the military brings regulatory infrastructure. Army and Navy reactor regulators were present throughout the INL test, building familiarity with Antares' design in parallel with their own licensing activities. The Navy has built roughly four and a half times as many reactors as the entire civilian sector and never stagnated the way the commercial industry did after the 1970s — making it a credible source of both operational expertise and regulatory throughput.

The underlying mission need is resilient power for assets that increasingly operate from continental US installations — command and control, satellite communications, cyber warfare, nuclear deterrence, space operations — all of which are vulnerable to adversary disruption of the civilian grid. Nuclear fission, Bramble argues, is the highest-capacity-factor energy source available today to sustain those assets without dependence on liquid fuel supply chains or commercial grid access.

The bet is that companies which win the data center and remote industrial markets will emerge from military work first, carrying more operator reps, more regulatory reps, and more demonstrated proof points at scale. With $140 million raised, Antares has 322,000 square feet of manufacturing space in Torrance and a tested system that has already run at full thermal power for six months using electrically heated cartridge heaters in place of nuclear fuel. The nuclear test at INL was the final integration step before electricity generation — and now it's done.