The Fourth of July 2026 marks a symbolic milestone for American nuclear power. Four microreactors, developed by as many startups, achieved zero-power criticality by the deadline set for the nation’s 250th birthday. The goal was established last year by the Trump administration, aiming for three new microreactors to reach this technical phase by the anniversary. The outcome exceeded expectations, but the path to electricity generation remains long.
The Microreactor Pilot Program: an unprecedented acceleration
The Reactor Pilot Program, launched by the U.S. Department of Energy in August 2025, selected eleven reactor projects for fast-track development. Participants received land and support from the national labs system. The microreactors involved are far smaller than the large light-water reactors that dominate the grid today. The initiative aimed to quickly test the technical feasibility of new nuclear technologies, in an industry notorious for delays and cost overruns.
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Four startups hit the target: Antares, Valar, Deployable, and Aalo
Antares Nuclear was the first to achieve criticality in June with its Mark-0 test reactor. Valar Atomics, Deployable Energy, and Aalo Atomics followed, with Aalo meeting the milestone in the early hours of July 4. The speed is remarkable: Valar, Antares, and Aalo were all founded in 2023, and Deployable started in 2025. However, zero-power criticality is only a startup test, with no useful heat production. As Kathryn Huff, former assistant secretary for nuclear energy, explained on a podcast, this milestone can be achieved without genuine engineering progress on fuel or design.
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From criticality to the grid: technical challenges and regulatory hurdles
Achieving zero-power criticality does not mean a reactor is ready to generate electricity. To produce power, companies must add cooling systems and other essential components. Aalo has already begun work on a second reactor and plans to produce 10 megawatts of electricity for an on-site data center by 2027. Deployable Energy aims to commercialize its reactors by 2028. However, startup timelines should be taken with caution, especially in the complex nuclear field. The Nuclear Regulatory Commission (NRC) has proposed a new framework for microreactor approvals, but the actual speed of procedures remains uncertain. Some experts have raised concerns about excessive deregulation, while the think tank Third Way calls the federal focus on microreactors an "unhelpful diversion" from goals to meaningfully increase nuclear capacity.
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The technological and regulatory challenges echo those in other high-innovation sectors. A related article on Red Hat examines cost and security obstacles for enterprise AI agents, parallels useful for understanding the difficulties in deploying new technologies. For more on nuclear criticality, see the Wikipedia page.
Source: https://www.technologyreview.com/2026/07/09/1140235/nuclear-reactor-milestone-criticality
