A US Startup Has Split The Atom And Achieved Criticality For The Very First Time

In the deserts of Nevada, a US startup has achieved cold criticality, a bold step in the development of a functional commercial nuclear reactor. It’s the first time a venture-backed startup has ever done this, and the company argues that its success marks "the dawn of a new era" in the US's efforts to spark a renaissance of nuclear energy. 

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Valar Atomics, a California-based company, has just announced that its NOVA Core reactor has successfully reached cold criticality. They say the feat was completed on the morning of November 17, 2025, at the Nevada National Security Site operated by Los Alamos National Laboratory.

Criticality occurs when a nuclear reactor sustains a self-perpetuating chain reaction of fissionable material. Within the NOVA Core, atoms of uranium-235 were split, releasing neutrons that go on to split more atoms, continuing the reaction like a domino effect.

Cold criticality, also called zero-power criticality, refers to a self-sustaining nuclear chain reaction that doesn't generate enough heat to actually make power. It’s a bit like a test run that allows the engineers to see how the core works without producing enough heat energy to require active cooling or reach full operating conditions.

“Zero power criticality is a reactor’s first heartbeat, proof the physics holds,” Isaiah Taylor, Founder and CEO of Valar Atomics, said in a statement. “I’m incredibly proud of the Valar team that took this from blueprint to splitting the atom, securing the first criticality ever achieved by a venture-backed company.” 

“This moment marks the dawn of a new era in American nuclear engineering — one defined by speed, scale, and private-sector execution with closer federal partnership,” he added.

The company did not do this alone. They received technical assistance from the Los Alamos National Laboratory (LANL), known for the nuclear weapons under the Manhattan Project during World War 2.

Along with LANL's expertise, Valar Atomics has recently pocketed $130 million of funding from several big dogs of American tech, including Anduril Industries founder Palmer Luckey and Palantir Chief Technology Officer Shyam Sankar.

Their breakthrough is part of the US Department of Energy’s (DOE) Reactor Pilot Program, an ambitious initiative to fast-track the development of advanced nuclear reactor designs by private companies and organizations outside of the national laboratories. Created through an executive order of President Donald Trump, it’s part of a wider program that’s been called the “Manhattan Project 2.0”, designed to kickstart a renaissance of nuclear energy and technology.

The DOE project set targets to have at least three start-ups achieve criticality by July 4, 2026 – and Valar Atomics has just become the first to reach that goal.

“President Trump asked industry and the labs to make nuclear great again. We got together and decided to start with the basics of fission. This team delivered incredible results safely so we can keep moving up the technical ladder,” commented Max Ukropina, Head of Projects at  Valar Atomics.

“America should be thrilled, but wanting more,” he added.