Ward 250

Executive Overview

Ward 250 is a 5 MW helium-cooled, graphite-moderated TRISO-fueled microreactor developed by Valar Atomics, selected by the U.S. Department of Energy in August 2025 under the DOE's Nuclear Reactor Pilot Program, launched under Executive Order 14301 signed in May 2025. The programme mandate requires at least three test reactors to achieve criticality on American soil by July 4, 2026. On November 17, 2025, Valar's NOVA Core — a full-scale physics model of the Ward250 core using the same TRISO fuel, graphite moderator, and control scheme — achieved zero-power criticality at Los Alamos National Laboratory's National Criticality Experiments Research Center, making Valar the first venture-backed company in U.S. history to achieve nuclear criticality. In February 2026 (Operation Windlord), the Ward250 reactor — eight modules, unfueled — was transported by three U.S. Air Force C-17 Globemaster III aircraft from March Air Reserve Base, California, to Hill Air Force Base, Utah — the first time a nuclear reactor has been transported by air. Testing is conducted at the Utah San Rafael Energy Lab (USREL) in Emery County, Utah.

How It Works & Differentiation

The Ward250 uses TRISO fuel pellets in a high-temperature helium-cooled reactor design operating above 750°C — the same fuel type as X-energy's Xe-100 — but packaged into a reactor assembly small enough to be loaded aboard a standard cargo aircraft in eight modules. Helium cooling avoids radioactive contamination of the coolant and enables high operating temperatures. TRISO fuel particles — uranium kernels encased in multiple ceramic layers — contain their own fission products, reducing the requirement for conventional large containment structures. The NOVA Core criticality experiment validated Valar's physics models and neutronics software ahead of Ward250 power operations, providing the performance data needed for fuel loading and temperature ramp-up at USREL.

Commercialization & Traction

Valar Atomics was selected alongside Terrestrial Energy, TRISO-X, and Oklo under the DOE pilot programme. The NOVA Core criticality milestone in November 2025 was the first criticality achieved under the DOE Reactor Pilot Program, and the C-17 airlift in February 2026 was the first air transport of a nuclear reactor in history. Valar is targeting power sales on a test basis in 2027 and full commercial operations in 2028. The July 4, 2026 target date is the criticality milestone — not commercial operation — and reflects the presidential-level political commitment in Executive Order 14301.

Scalability & Strategic Context

The Ward250's air-transportability is the defining commercial proposition: it can be flown to any location a C-17 can reach within hours, providing firm power in remote, contested, or disaster-affected environments where grid connection and fuel supply chains are unreliable. The 5 MW output is calibrated for forward operating base power requirements. Successful full criticality at USREL in 2026 would provide the nuclear data needed to pursue an NRC operating licence under the reformed regulatory framework and follow-on DoD procurement. Valar's longer-term commercial vision is factory-built clusters of high-temperature reactors — ‘gigasites’ — serving data centres, hydrogen production, and industrial heat at scale.