Three private nuclear microreactors reached criticality within thirty days, all before June 30, 2026. It is an absolute world first. The U.S. Department of Energy hit its target four days ahead of the July 4 deadline — marking the 250th anniversary of the United States.
The timeline is precise. Antares Nuclear kicked things off on June 4 with its Mark-0 at Idaho National Laboratory: the 53rd reactor ever built on the site since 1951, and the first private non-light-water reactor to achieve criticality there in over fifty years. The design uses sodium heat pipes and is passively cooled with no high-pressure pumps. On June 18, Valar Atomics followed with its Ward 250, a high-temperature helium-cooled reactor using TRISO fuel, which became the first reactor to achieve criticality outside a national laboratory — at a state-licensed site in Utah. Moving it from California required three C-17 military transport aircraft. On June 30, just hours before midnight, Deployable Energy completed the trio with its Unity Nuclear Battery, a 1 MWe reactor that fits inside a standard shipping container. Founder Bobby Gallagher, keen to prove the system’s portability, loaded the reactor core onto a Ford F-150 pickup and drove it from Houston to Idaho. Unity reached criticality in roughly 150 days from project launch, on a budget of just a few million dollars.
The foundation for all of this is Executive Order 14301, signed by President Trump on May 23, 2025, which directed the DOE to establish a Reactor Pilot Program and bring at least three advanced reactors to criticality by July 4, 2026. When the goal was announced, much of the industry dismissed it as unrealistic — conventional wisdom holds that a new reactor takes at least a decade to develop. The DOE instead selected 11 projects from 10 companies in August 2025, bypassing the Nuclear Regulatory Commission’s traditional licensing process — which required more than 20,000 hours — and centralizing oversight within the Department of Energy. That regulatory shortcut made otherwise unthinkable timelines possible.
These machines bear little resemblance to anything conventionally called a nuclear power plant. Antares’ Mark-0 is designed to deliver 100 kilowatts to a future lunar base and has already been ordered by Joint Base San Antonio for 2027. Valar’s Ward 250 had already reached 10 kWt thermal output within days of achieving criticality, with a target of 100 kWt. Deployable’s Unity can power roughly 800 homes or a mid-sized data center. Radiant Industries, with its container-deployable Kaleidos, is targeting 150 consecutive hours of full-power operation with no human intervention. The data center sector and major hyperscalers are already exploring procurement options: demand for guaranteed, anywhere-deployable power has never carried more weight.
Zero-power criticality is only the first step. None of these reactors yet generates commercial electricity, and obtaining an NRC operating license remains a mandatory hurdle. Deployable Energy plans to submit its commercial license application by year-end, with a projected six-to-twelve-month review timeline. But the significance goes beyond the technical. Four companies brought four first-generation reactors to criticality in a single month — more genuine milestones than the industry had produced in the preceding decades combined. If even one of these designs succeeds in obtaining a license, delivering a working reactor to a paying customer, and proving its economic viability, the way the world builds and deploys nuclear energy will change in a concrete and measurable way.
