Four private nuclear reactors achieved criticality in the United States before July 4, 2026 — the 250th anniversary of American independence. President Trump’s Executive Order 14301, signed in May 2025, had set a target of at least three. Four made it.
The companies involved are Antares Nuclear, Valar Atomics, Deployable Energy, and Aalo Atomics. Antares crossed the finish line first: its Mark-0 reactor achieved criticality on June 4 at Idaho National Laboratory, becoming the 53rd reactor in the lab’s history and the first non-light-water reactor fully funded by private capital to do so in four decades. Valar Atomics followed on June 18 with its Ward 250 — a helium-cooled, TRISO-fueled reactor — which reached criticality outside a national laboratory, at the Utah San Rafael Energy Lab, marking a first under any DOE program. On June 22, the Ward 250 generated 10 kilowatts of thermal power, converted to electricity and fed to an Nvidia Spark chip, as part of a Valar-Nvidia agreement to build a 30-megawatt nuclear data center in Utah. On June 30, it was Unity‘s turn — Deployable Energy’s 1-megawatt microreactor, built in roughly 150 days on a budget in the millions of dollars, with a core compact enough to be transported to Idaho in a pickup truck bed. Finally, in the early hours of July 4, at 12:20 a.m. Mountain Time, Aalo Atomics’ test reactor completed the quartet.
The Department of Energy managed this cycle through two separate programs. The Reactor Pilot Program, established in June 2025, authorized Antares and Valar. The Nuclear Energy Launch Pad, launched in March 2026 and operated by the National Reactor Innovation Center at Idaho National Laboratory, supported Deployable Energy — the first project to cross the milestone under this new initiative — and subsequently Aalo. The two programs are complementary: the Launch Pad extends the opportunities of the pilot program to companies not originally selected, and covers federal sites beyond INL.
Aalo Atomics reported that its Critical Test Reactor went from groundbreaking to sustained chain reaction in under eight months, one of the shortest construction timelines in the past eighty years. The company has already begun work on its second reactor under Project Ascension and is expanding manufacturing capacity at a one-million-square-foot facility to produce the Aalo Pod, a 50-megawatt modular plant designed for AI data centers. Deployable Energy is targeting commercial deployment by 2028. Antares has already begun work on the Mark-1, its electricity-generating prototype, with its CEO confirming commercial deliveries by the same year. Energy Secretary Chris Wright has said he expects the first electricity from a private SMR by 2027, and certainly by 2028.
No country had ever brought three distinct advanced microreactor designs to criticality within a single month. The next step — adding heat conversion and cooling systems to generate net electricity — still requires substantial engineering work. But the milestone that matters right now is this: these companies have proven that timelines and costs once considered impossible are, in fact, achievable. Markets have already taken note. Following its criticality achievement, Valar raised $450 million at a $2 billion valuation. The era of privately-led, industrial-scale nuclear power generation has begun — even if the gap between a zero-power test and a grid-connected reactor still has to be crossed.
