New Atomic Age Underway As Three Mini Reactors Go ‘Critical’ By Trump’s July 4 Deadline

All 200 employees from nuclear startup Aalo Atomics’s Austin, Texas headquarters have been flying into Idaho Falls this week to gather at the two-acre construction site, just outside of the Department of Energy’s Idaho National Laboratory, where their new Aalo-X reactor is now being put to the test. Aalo brought in Airstream trailers for the event, which CEO Matt Loszak describes as “a nuclear Burning Man,” after the counter culture festival in the Nevada desert.

“We’ll give some emotional speeches,” says Loszak of himself and his co-founder Yasir Arafat, and share a live video feed of the team loading uranium fuel bundles into the reactor core, then removing control rods to allow fission chain reactions to speed up.

Aalo broke ground on the DOE site in August 2025 with the ambitious plan to achieve “criticality” -- the state in which a nuclear reactor sustains a stable chain reaction -- by July 4, 2026. Early on July 2, Aalo’s Arafat, the chief technology officer, conceded in a post on X that they weren't quite to critical yet. “Atoms are splitting, and the core is multiplying neutrons, but we're not critical yet….criticality is a slow and deliberate process. And we are super close to the July 4th deadline.”

America’s 250th birthday is the deadline President Donald Trump set in a May 2025 executive order directing the DOE to launch the Reactor Pilot Program, with the goal of jumpstarting at least three reactor startups to achieve criticality. Aalo is just the latest small-sized reactor startup to close in on “criticality,” thanks to help from the DOE. Incredibly, three others recently achieved the milestone, satisfying Trump’s deadline -- Valar Atomics, Antares Energy and Deployable Energy.

Bob Boston, head of the agency’s Idaho Operations Office and a four-decade nuclear industry veteran, told Forbes in March that helping to steer these reactor pilots has been the busiest time of his career. Much of the testing on microreactors has taken place on the grounds of Idaho lab underneath the protective containment dome built in the 1960s to house the Experimental Breeder Reactor II.

“There’s nowhere else in the world that this could happen. The U.S. is still the leader in nuclear, by the skin of our teeth,” says Loszak.

Valar Atomics
Nuclear startup, El-Segundo, Calif.-based Valar Atomics has already achieved criticality twice. The first time was at the Los Alamos National Laboratory with just the core of their reactor. The second time was in June, at the test facility Valar built at the San Rafael Energy Lab in Utah to house its Ward250 reactor, roughly the size of a minivan. Valar founder Isaiah Taylor (a Forbes 30 Under 30 list member last year) got some moving assistance from the Air Force which in February flew equipment from southern California in three C-17 cargo planes. A month after that event Valar raised $450 million at a $2 billion valuation. And on July 1 it announced a massive deal to build a 30 megawatt nuclear-powered datacenter with Nvidia in Utah.

Antares Energy
The Mark-0 reactor built by Torrance, Calif-based Antares Energy, in early June became the 53rd-ever reactor ever to achieve criticality at Idaho National Lab, according to the DOE, but the first privately funded non-light-water reactor to do so in four decades. Three-year-old startup Antares has also been testing its microreactor at NASA’s Marshall Space Flight Center in Huntsville, Alabama, with the aim of providing 100 kilowatts of reliable power to a future moon base. The military is interested in slightly less remote deployments; Antares already has an order to deliver reactors to Joint Base San Antonio in 2027.

Deployable Energy
Founded just a year ago by Bobby Gallagher who served in the Australian Army and built offshore oil rigs, Deployable energy set out to make a compact, modular, transportable microreactor that could be delivered fast, on budget and where needed. The Houston-based outfit has emerged as a wildcard from a newer DOE program called Launch Pad, started just last March. Deployment partnered with the nuclear engineering department at Texas A&M to create its 1 megawatt shipping-container reactor called Unity Nuclear Battery. To demonstrate how easily portable his reactor is, Gallagher drove the core of the machine to Idaho Falls in the back of a Ford F-150. According to the DOE, Deployable achieved criticality June 30.

Up To Bat:
The next successful criticality test will likely come from Radiant, which has also devised a shipping-container reactor called Kaleidos. El Segundo-based Radiant is also working within the Idaho National Lab, but intends to take its testing farther than the zero-power criticality tests by Valar, Antares and Aalo. Radiant aims to ramp up its helium-cooled reactor to attain full heat, full power and operate at 1 mw for 150 hours without operator intervention. Radiant is also building a factory near Oak Ridge, Tennessee to manufacture 50 reactors a year. Some of the first ones are already earmarked for 2028 delivery to the Buckley Space Force base in Aurora, Colo.

Another to watch include Berkeley-based Deep Fission, which has bored its first 6,000 foot deep hole in Kansas where it plans to lower its first reactor – with the pressure of the Earth providing protective containment. In time a field with a few dozen boreholes could hold enough reactors to power a datacenter, according to the father-daughter team that started the company UC Berkeley physics professor emeritus Richard Muller and daughter Liz. The 4-year-old company, which went public June 18, is worth $600 million, even after its shares dropped about 40% since the IPO.

Then there’s Kairos Power, whose cofounder and CEO Mike Laufer told Forbes last year that he wasn’t that interested in the criticality sideshow, because he's past that point. Kairos, founded 2016, was the first small nuke developer to get federal permits to build a new reactor design, and is now simultaneously erecting the Hermes 1 pilot plant and Hermes 2 reactors near the Oak Ridge National Lab in Tennessee. At 50 megawatts Hermes 2 will be on the big side compared with the rest of the crop of new reactors. Kairos is set to receive $300 million in milestone based payments from the DOE in support of the project, which will sell electricity to the Tennessee Valley Authority, in part to power nearby Google datacenters -- hopefully as early as 2030.

To be sure, none of these new reactors have yet been proven to operate at full power for an extended period, let alone generate electricity in sufficient quantities to power anything at all. Most of these designs will require new fangled pellets of meltdown-proof uranium fuel called TRISO that aren't even available yet.

Demand is there if they can make it all work. Amazon has committed to buying 5 gigawatts of reactors from another startup X-Energy, which raised $1 billion in an April IPO and now sports a market cap of $9 billion. Meanwhile Deep Fission in June announced letters of intent from customers looking to buy an outlandish 18.5 gigawatts of their nuclear reactors. That’s enough to power New York City two times over, on all but the hottest days.