A second privately built nuclear reactor went critical this week in Utah. Less than three weeks ago, Antares Nuclear did it in Idaho, the first privately developed non-light-water reactor to reach criticality in the United States in more than 40 years. Now, Valar Atomics has done it too. The Trump administration set a July 4 deadline. Two companies have hit it.
The Ward 250 reactor completed a zero-power fueled criticality demonstration at the Utah San Rafael Energy Lab. DOE says it is the first reactor built and operated outside a national laboratory under Department of Energy (DOE) authorization.
Valar was founded in 2023. Stayed in stealth until February 2025. Broke ground in Emery County that September on what was, at that point, an empty field. Nine months later, the reactor on that site reached criticality.
Isaiah Taylor, Valar’s founder and CEO, demonstrated the timeline:
“Nine months ago, this was an empty site. Today, there’s a critical reactor on it, built and operated by the Valar team. We met the milestone the executive order set. This reactor was built to make power, and that’s exactly where we’re headed.”
Ward 250 is a high-temperature gas-cooled reactor with tri-structural isotropic (TRISO) fuel, helium coolant, and graphite moderation. Compact enough to ship in a minivan-sized envelope, designed to be operated remotely, and intended to scale to five megawatts of electricity when fully developed.
Before moving the full reactor to Utah, Valar ran a smaller test configuration, the NOVA Core, at the National Criticality Experiments Research Center in December 2025. Zero-power criticality. Physics confirmed. Then they built the real thing.
Getting Ward 250 to Utah required three U.S. Air Force C-17 Globemaster IIIs. The unfueled components were loaded in California and flown to the test site. DOE says it was the first time a small reactor had been airlifted on a U.S. military C-17.