Legal Insurrection recently reported that American energy development cleared a major technical hurdle after Antares Nuclear’s Mark-0 microreactor achieved zero-power criticality under the Department of Energy (DOE) Reactor Pilot Program (RPP).
The successful test marked the first advanced reactor to meet the ambitious July 4, 2026, deadline set by President Trump’s 2025 executive order to accelerate next-generation nuclear deployment.
Now, there is another.
Valar Atomics’ Ward 250 advanced reactor is now officially the second major success under the RPP, after the reactor completed a zero‑power fueled criticality demonstration at the San Rafael Energy Lab in Emery County, Utah.
Valar Atomics announced that its Ward 250 nuclear reactor has reached self-sustaining criticality and completed zero-power testing in a Utah energy lab ahead of the July 4 deadline.President Donald J. Trump signed an executive order in May 2025 reforming nuclear reactor testing at the Department of Energy. As part of that order, Valar Atomics was given a deadline of July 4 to have an operating reactor on United States soil. This deadline has been met.Ward 250 reportedly reached these milestones as a complete, fully integrated system configured for power operations.
Ward 250 is a Gen IV Reactor, which is the next phase of reactor development that targets improvements in safety, sustainability, economics, and proliferation resistance beyond current Gen II/III light‑water reactors. It is a TRISO (TRI-ISOtopic)-fueled modular high-temperature gas reactor (HTGR) that uses helium coolant, graphite-moderated cores, and ceramic TRISO particle fuel to produce very high temperatures in factory-built modules, with strong inherent and passive safety characteristics.
The firm’s goal is to power operation, not merely achieve criticality, by the July 4th deadline. The systems are reported to be in place to make it happen, which would be a significant leap forward for the RPP.
Ward 250, an HTGR rated at 100 kWt initial test power and scalable to 5 MWe, uses helium coolant and TRISO fuel particles in Advanced Gas-Cooled Reactor (AGR) compacts, according to an October 2025 Valar quality-assurance program description. The document says Ward 250 incorporates passive safety features and builds on WardZero prototype technology, while the co-located Valarin Fuel Fabrication Facility is designed to manufacture TRISO-coated particle fuel embedded in graphite compacts using German HOBEG technology with modern process improvements. Kiewit Nuclear Solutions served as the project’s engineering, procurement, and construction contractor.
“Criticality proves the physics; power operations prove the engineering,” Valar said. “Power operations require cooling, instrumentation, controls, advanced shielding, and power conversion to function together as a complete system. Ward 250 went critical with those systems integrated and in place.”
Valar received preliminary DSA approval in February 2026 and final DSA approval on April 23, which cleared the last design gate before DOE’s Operational Readiness Review. The company had said in May that its July 4 target was power operations, not zero-power criticality, calling that step “a massive leap in capability and complexity.”
The DOE noted this achievement, and this unit is the first DOE-authorized reactor built outside a national laboratory.
“Today marks another historic moment for America’s nuclear renaissance,” said U.S. Energy Secretary Chris Wright. “From the first-ever airlift of a small reactor aboard a U.S. military C-17 to successful zero-power criticality testing, Valar Atomics is delivering achievements that mark a revolutionary moment for advanced nuclear in this country. The Trump administration is proud to support the rebirth of America’s nuclear industry, ensuring Americans have access to affordable, reliable and secure energy for generations to come.”In June, Antares Nuclear’s Mark-0 reactor achieved criticality at Idaho National Laboratory.Beyond making Ward 250 the second advanced reactor to reach criticality under the federal timeline, DOE said the demonstration marks the first DOE-authorized reactor built outside a national laboratory.
Valar Atomic CEO Isaiah Taylor and the firm’s Nuclear Officer Mark Mitchell offered a video introduction to their company, for those who are interested in more background:
Ward 250’s success underscores that Trump’s ambitious nuclear acceleration order is not just visionary rhetoric but an emerging reality, as next‑generation reactors move from paper designs to powered hardware on American soil.
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