Aalo Atomics' Aalo-X test reactor reached zero-power criticality early Saturday at Idaho National Laboratory, the fourth advanced reactor design to hit that milestone under the U.S. Department of Energy's Reactor Pilot Program. The result beats the target in President Trump's May 2025 executive order, which called for three reactors to reach criticality by the Fourth of July.
Zero-power fueled criticality is the point at which a nuclear reaction becomes self-sustaining without yet producing power for the grid. It is a standard early step before a reactor design moves toward full power operation.
Three other reactors cleared the bar in June
Aalo-X follows three other designs that reached criticality in June under the same program: Antares Nuclear's Mark-0, Valar Atomics' Ward 250, and Deployable Energy's Unity. All four sit under the DOE's Reactor Pilot Program, which authorizes and helps construct first-of-a-kind advanced reactor designs for demonstration. The department runs the program alongside its Nuclear Energy Launch Pad initiative.
Energy Secretary Chris Wright toured Aalo Atomics' Idaho facility last month and said he was impressed by the company's push to demonstrate its technology by the Fourth of July. "President Trump asked for three advanced reactors to be authorized and achieve criticality by the 250th anniversary of our great country," Wright said. "We have surpassed that ask and delivered four."
Aalo Atomics President and CTO Yasir Arafat said the company went from breaking ground to a sustained chain reaction in eight months, one of the fastest reactor builds in modern American history, according to the company. "The hardest problem in nuclear was never the physics," Arafat said, adding that the country had simply forgotten how to build and that the program's run of results is "proof America can execute again."
What the pilot program does
The Reactor Pilot Program uses DOE authorization to move first-of-a-kind reactor designs from construction to demonstration faster. The DOE casts the approach as part of the Trump administration's energy policy push, and says it is meant to help usher in what it calls a golden age for the nuclear industry.
