The United States has quietly achieved another milestone in advanced nuclear energy. Three experimental microreactors have reached criticality, allowing them to sustain a controlled nuclear chain reaction. Supported by the Department of Energy, the projects are drawing interest as electricity demand from data centers continues to rise.
The newest reactor to reach criticality is Unity, a microreactor developed by Houston-based Deployable Energy. The achievement came through a Department of Energy program focused on advancing next-generation nuclear technology. It follows similar successes by reactors from Torrance-based Antares and El Segundo-based Valar Atomics, both of which reached criticality in June.
Unlike conventional nuclear power plants, these reactors are much smaller and are not intended to generate electricity for the grid. Their role is to test new reactor designs and fuel technologies that could make future nuclear projects easier, faster, and more affordable to deploy.
The achievements were made possible through more than financial support from the federal government. The Department of Energy provided Antares and Deployable with access to its national laboratories, completed safety evaluations, and approved the reactors to reach criticality. Unity is currently being tested at Idaho National Laboratory.
Bobby Gallagher, CEO and co-founder of Deployable, credited the achievement to the Department of Energy’s commitment to safety, quality, and timely execution, as well as the support provided by staff at the national laboratory.
The administration wants to bring nuclear power back into the spotlight after years of slow growth. Its goal is to boost U.S. nuclear capacity to 400 gigawatts by 2050. A big reason is the growing demand for electricity, especially from AI and cloud data centers. Some companies are already exploring microreactors and small modular reactors to power those facilities, and the Department of Energy says several pilot projects are already talking with data center operators.
Michael Goff, principal deputy assistant secretary in the DOE’s Office of Nuclear Energy, told Politico that the speed of recent progress challenges old assumptions. “The fact that they can do this and do this so quickly, it shows that the preconceived notions we’ve had about nuclear are no longer valid anymore,” Goff said. “Nuclear doesn’t have to take a long time if we have the right enabling environment to move forward. Nuclear can move forward fairly rapidly.”
The reactor deployments are taking place under two different Department of Energy initiatives. Aalo Atomics is participating in a pilot program introduced last year, while Deployable’s reactor is being developed through a separate initiative launched in March. Both programs are intended to help companies advance from early designs to demonstration projects and, ultimately, commercial deployment.
None of the microreactors or small modular reactors under development is operating commercially in the United States yet. Before they can become commercial power plants, developers must secure approval from the Nuclear Regulatory Commission. The agency is also updating its licensing process following a White House directive and the bipartisan ADVANCE Act, passed in 2024, which calls for faster reviews of advanced reactor technologies.
According to DOE officials, including Energy Secretary Chris Wright, the Nuclear Regulatory Commission has been engaged throughout the demonstration phase. Michael Goff said that early collaboration could help shorten the commercial licensing process. A proposed rule would create a faster approval pathway for advanced reactors that have already undergone review by the Department of Energy or the Department of Defense. Deployable CEO Bobby Gallagher said the company intends to apply for a commercial license later this year after new licensing regulations are finalized, with NRC approval expected within six to twelve months.
Despite the momentum, people inside and outside the sector caution that successful tests are not the same as a commercial breakthrough.
Emily Tucker, vice president on the energy team at advisory firm Capstone, said the criticality milestones matter from a technology and demonstration standpoint, but do not signal that commercialization is near. Alison Hahn, a former head of advanced reactors at DOE who is now a senior director at the Nuclear Energy Institute, noted that the pilot program is explicitly for demonstration reactors, not for delivering commercial power to the grid, though it does move the industry forward technically and in terms of building out the supply chain.
Several challenges still need to be addressed. Some advanced reactor designs require high-assay low-enriched uranium (HALEU), which is not yet commercially available in the United States. Without a reliable domestic fuel supply, scaling up deployment will be difficult. The smallest microreactors also may not produce enough electricity to support the energy needs of large data centers on their own.
James Richards, manager of economics and project development at the Nuclear Innovation Alliance, said scaling up remains a major challenge. “It’ll be incumbent on these companies to really take what they’ve learned and actually kind of apply that in a scaled-up production,” he said. “That’s not a given. That’s still a very difficult task.”
Financing remains another major hurdle. The DOE’s pilot program does not cover construction costs, and Deployable built its reactor without federal funding. Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists, argued that the program offers visibility but little financial support. He said the biggest barrier to deploying new reactors is securing the billions of dollars needed to build them, even at a smaller scale.
The DOE’s emphasis on reaching criticality has also faced criticism from some supporters of nuclear energy. The center-left nonprofit Third Way argues that the pilot program has become a distraction from the broader goal of expanding commercial nuclear power. While achieving criticality provides valuable data on new fuels and reactor designs, the group says it should not be mistaken for a commercial milestone.
Goff acknowledged that reaching criticality is only a starting point. “We’ve got to go beyond criticality,” he said. “If we were just focused on criticality, I think it might just be misplaced.”
Despite the challenges, Goff believes advanced reactors could begin supplying electricity in the United States before the end of the decade. He said several companies participating in DOE pilot programs are already in discussions with data center developers and expects those partnerships to be announced in the near future.
A successful demonstration is only the beginning, and widespread commercial deployment of microreactors remains years away. Even so, three reactors reaching criticality in a short period marks steady progress for an industry searching for reliable, carbon-free sources of electricity.
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