Valar Atomics achieves criticality in DOE Reactor Pilot Program

Valor Atomics was one of the first group of companies selected last year for the US Department of Energy's Reactor Pilot Program.

The programme, announced in June 2025, aims to expedite the testing of advanced reactor designs that will be authorised by the Department at sites located outside of the national laboratories. Part of the Reforming Nuclear Reactor Testing at the Department of Energy executive order signed by President Donald Trump in May, its goal is "to construct, operate, and achieve criticality of at least three test reactors using the DOE authorisation process by July 4, 2026".

Criticality means that the reactor has achieved a sustained nuclear chain reaction, with each fission event - when an atom of uranium in the fuel is split - releasing a sufficient number of neutrons to sustain an ongoing series of reactions. In a nuclear power reactor, the heat energy from those fission reactions is used to produce steam and generate electricity. Zero-power - or "cold" - criticality is a self-sustaining chain reaction of uranium-235 within a nuclear core, but without reaching full operating temperatures or actively removing heat with a working fluid.

Valar, a startup launched in 2023, plans to build nuclear "gigasites" with "clusters of thousands of high-temperature reactors designed to supply the energy, industrial heat, and carbon-neutral fuels that modern industry and AI infrastructure demand". It says its TRISO (tri-structural isotropic) fuelled, helium-cooled and graphite-moderated reactors are "inherently safe and capable of operating at much higher temperatures than conventional plants".

The 5 MW Ward 250 reactor, which was transported by US Air Force cargo plane from California to its base at the Utah San Rafael Energy Lab in Emery County, Utah, in February, could provide power to about 5,000 homes. For military use, such a reactor could provide energy security on a military base ensuring the mission there need not depend on the civilian power grid, and in military operations overseas, such transportable microreactrors would mean US forces could operate without concern that an enemy might cut fuel supplies.

US Energy Secretary Chris Wright said: "Today marks another historic moment for America's nuclear renaissance. From the first-ever airlift of a small reactor aboard a US 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."

Isaiah Taylor, Founder & CEO of Valar Atomics, said: "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."

Earlier this month Antares Nuclear's Mark-0 reactor completed a zero-power fuelled criticality demonstration, to become the first of the programme’s reactors to meet the pre-4 July deadline.