Valar Atomics has achieved self-sustaining criticality with Ward 250, its Gen IV TRISO-fueled high-temperature gas reactor, at the Utah San Rafael Energy Lab in Emery County — the second advanced reactor to go critical under the U.S. Department of Energy's Reactor Pilot Program, and the first DOE-authorized reactor built and operated outside the national laboratory system.
A Zero-Power Milestone With a Deadline Attached
The DOE's Office of Nuclear Energy confirmed the zero-power fueled criticality demonstration at about 4:30 p.m. MDT on June 18. The milestone counts toward Executive Order 14301, which directed the DOE to achieve criticality on at least three advanced reactors by July 4, 2026. Antares Nuclear's Mark-0, a sodium heat-pipe-cooled microreactor, was the first to clear the bar on June 4 at Idaho National Laboratory; candidates for the third slot include Aalo Atomics' sodium-cooled test reactor at INL and Oklo's Atomic Alchemy isotope reactor in Texas.
From Empty Site to Critical Reactor in Nine Months
Ward 250 is a helium-cooled HTGR rated at 100 kWt initial test power and scalable to 5 MWe, using TRISO fuel particles with passive safety features. The reactor was airlifted from California to Utah in February aboard three C-17 Globemaster III aircraft in Operation Windlord — the first military airlift of a nuclear reactor. Kiewit Nuclear Solutions served as EPC contractor.
"Nine months ago, this was an empty site. Today, there's a critical reactor on it, built and operated by the Valar team," said founder and CEO Isaiah Taylor. "This reactor was built to make power, and that's exactly where we're headed." The company, founded in 2023 and reportedly valued at $2 billion after a $450 million raise, has now begun non-commercial power ascension testing.
Nuclear's Startup Moment
The Reactor Pilot Program's DOE-authorization pathway has compressed timelines that once took a decade into months, and Utah is leveraging Ward 250 as the anchor of its Operation Gigawatt energy strategy. Grid-hungry AI data centers are a major driver — the same demand pull behind General Fusion's LM26 plasma milestone and grid-scale buildouts like GE Vernova's new turbine platform in India. Valar says Ward 250 will run a series of experiments in the weeks ahead as it climbs toward power operations.
Reporting based on coverage from POWER Magazine, the U.S. Department of Energy and World Nuclear News.