Startup Valar Atomics said on Monday that it achieved criticality—an essential nuclear milestone—with the help of one of the country’s top nuclear laboratories. The El Segundo, California-based startup, which last week announced it had secured a $130 million funding round with backing from Palmer Luckey and Palantir CTO Shyam Sankar, claims that it is the first nuclear startup to create a critical fission reaction.
It’s also, more specifically, the first company in a special Department of Energy pilot program aiming to get at least three startups to criticality by July 4 of next year to announce it had achieved this reaction. The pilot program, which was formed following an executive order president Donald Trump signed in May, has upended US regulation of nuclear startups, allowing companies to reach new milestones like criticality at a rapid pace.
“Zero power criticality is a reactor’s first heartbeat, proof the physics holds,” Valar founder Isaiah Taylor said in a statement. “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.”
Criticality is the term used for when a nuclear reactor is sustaining a chain reaction—the first step in providing power. Enriched nuclear fuel releases neutrons, which hit other atoms, which then split apart; neutrons from that process then hit other atoms, and start the reaction over. This process is known as fission. A properly-functioning reactor has just enough reactions to keep that fission chain going, reaching a state of criticality.
“Think of a long chain of dominoes,” says Adam Stein, the director of the Nuclear Energy Innovation program at the Breakthrough Institute, an eco-modernist policy center. “If you have those dominoes spaced out too far, a domino won’t hit the next one. If they’re spaced just right, then one hits the next, hits the next, and you have the reaction you’re hoping for.”
There’s a difference between the type of criticality Valar reached this week—what’s known as cold criticality or zero-power criticality—and what’s needed to actually create nuclear power. Nuclear reactors use heat to create power, but in cold criticality, which is used to test a reactor’s design and physics, the reaction isn’t strong enough to create enough heat to make power.
The reactor that reached criticality this week is not actually Valar’s own model, but rather a blend of the startup’s fuel and technology with key structural components provided by the Los Alamos National Laboratory, one of the DOE’s research and development laboratories. The combination reactor builds off a separate fuel test performed last year at the laboratory, using fuel similar to that Valar’s reactor will use.
The milestone is still a big one for Valar, which only came out of stealth earlier this year. Unlike some of the other startups involved in the DOE pilot program, the type of fuel Valar is using has had relatively little testing. Running cold criticality tests to make sure that the fuel geometry works with the reactor technology, Stein says, is a “prudent” choice for the company right now.
The DOE’s pilot program is helping several of the involved startups move “at speeds not seen since the Manhattan Project,” as Nuclear NewsWire put it in a piece published Monday. Even in this ambitious field, Valar stands out for its aggressive goals: The company announced in May that it intends to turn on a fully-functional model of its reactor by the July 4 deadline of next year. It started breaking ground at the intended site in late September.
Before this year, startups like Valar would have to go through the country’s nuclear regulator, the Nuclear Regulatory Commission (NRC), before trying any criticality tests. The NRC, which has a lengthy licensing process, traditionally maintains authority over all nuclear reactors. This includes small modular reactors, which, as their name suggests, are much smaller than traditional nuclear reactors; these advanced technologies, like the ones Valar is trying to bring to market, have never been commercially deployed in the US. However, both the Department of Defense and the Department of Energy have some legal ability to develop their own reactors without going through the NRC, including some solely used for research purposes.
The Trump administration has aggressively encouraged new nuclear power—and appears to be remaking much of how the country regulates it, especially when it comes to advanced reactor technologies. In response to a series of executive orders signed in May, the DOE created a pilot program to enable a group of 11 nuclear startups, including Valar, to develop their reactors in a research capacity, bypassing the lengthy and complex NRC review as they work out kinks in their technology. The program, the DOE said, would aim to get at least three startups to reach criticality by July 4, 2026—a date explicitly written out as a goal in one of the president’s executive orders.
“In the past, the first iteration of a design was a first-of-its kind from zero to a commercial product, and you didn’t get to test much beforehand,” Stein says. With the executive order, “the legal framing [for nuclear power] hasn’t shifted, but the mindset of how to interpret that has shifted,” he explains. “It basically asserted that if [a reactor] hasn’t been deployed commercially yet, then it is inherently a research system.”
For years, nuclear boosters have criticized the NRC for what they say is an overly complex application process and a hostile environment for nuclear companies, especially those seeking to develop advanced reactor technologies. Valar is one of three startups involved in a lawsuit filed late last year with a handful of red states against the NRC, claiming that the agency “so restrictively regulates new nuclear reactor construction that it rarely happens at all.” The suit challenges the NRC’s ability to regulate smaller reactors in any capacity, claiming that the risk for large-scale disasters with these reactors is so low that the NRC shouldn’t have any role in rubber-stamping them.
The other two startups on the lawsuit, Last Energy and Deep Fission, were also selected for the DOE pilot program. A recent Bloomberg Businessweek investigation found that a key investor in Silicon Valley darling Oklo—another DOE pilot project choice, whose application to the NRC was denied in 2022—was one of the driving forces behind the lawsuit. (Current DOE secretary Chris Wright is a former Oklo board member.) The Trump administration has seemed to agree with many of the critiques of the NRC: One of the executive orders signed in May ordered “sweeping reforms” of the agency, and in July, the president fired one of the members of the five-person board of regulators.
Achieving a milestone like cold criticality doesn’t mean that a commercial reactor is coming any time soon. Before going to market, Valar and other startups will have to re-engage with the NRC to license their reactors for commercial use.
Improvements in computer modeling, Stein says, has made perfecting the software before a real-life criticality test much easier than it was decades ago. But even some of the startups involved in the DOE pilot program have admitted that shooting for criticality within a year is an aggressive timeline. (Wright seemed to slightly walk back this timeline earlier this month, saying that he expects just one or two companies will get to criticality by July 4—but told an audience at a gala last week put on by the conservative Foundation for American Innovation that he thinks 10 startups will achieve criticality in the next two years.) In a blog post published last month, Stein wrote that while the pilot program “could be one of the most consequential steps for advanced nuclear in decades,” he worries that an arbitrary timeline “is trying to move reactors forward on a political schedule.”
Valar founder Isaiah Taylor told WIRED in an emailed statement that the DOE program “is about creating a predictable framework so companies and national labs can actually plan work,” and that the program “gives us access to sites, national lab expertise, and federal oversight that ensure each stage is done correctly.”
“We’ve moved quickly because we’ve invested heavily in our modeling, simulation, core design, and non-nuclear prototyping,” he says. “And we have the best team who are making this their life’s work. Our schedule is set by engineering readiness and safety validation with our federal partners, not politics.”
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