TL;DR
Three US nuclear startups have reached criticality in their reactors, a key milestone in the Department of Energy’s efforts to revive nuclear innovation. While promising, significant regulatory, technical, and economic challenges remain before these reactors can supply power commercially.
Three American nuclear startups have successfully turned on new reactors as part of a Department of Energy pilot program, marking a significant milestone in efforts to accelerate nuclear innovation and demonstrate new reactor designs. This achievement, announced in early July 2026, underscores a push by the US government to revitalize nuclear energy and reduce reliance on traditional large reactors.
The three startups—Valar Atomics, Antares Nuclear, and Deployable Energy—reached criticality at national laboratories or designated sites, with Valar Atomics achieving the milestone at Los Alamos National Laboratory and Utah earlier this month. Criticality indicates that the reactors can sustain a controlled nuclear chain reaction, a key step toward potential power generation.
These reactors are part of a broader initiative launched by the Biden administration, which aims to demonstrate faster development pathways and reduce regulatory hurdles. The pilot program was accelerated by an executive order issued in May 2025, setting an ambitious goal to have at least three reactors critical by July 4, 2026. The Department of Energy also relaxed some environmental and safety regulations, aiming to speed up licensing and construction processes.
Despite the milestone, experts emphasize that these reactors are still prototypes and not yet commercially viable. They have not yet been connected to the grid or used to power data centers or other operations. Regulatory approval, supply chain development, and final licensing remain significant hurdles before these reactors can be deployed at scale.
Implications for Nuclear Innovation and Industry Perception
The successful activation of reactors by these startups signals a potential shift in the nuclear industry, challenging the long-standing perception that new reactor development is slow and expensive. It demonstrates that, with regulatory reforms and government support, smaller and innovative reactor designs can reach critical milestones faster than historically possible.
However, industry experts caution that reaching criticality does not equate to commercial readiness. The reactors still face licensing, supply chain, and economic challenges. Investors and policymakers are watching closely, as these developments could influence future funding, regulation, and public perception of nuclear energy’s role in a low-carbon energy future.
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Background on US Nuclear Innovation Efforts
For decades, the US nuclear industry has been dominated by large, traditional light-water reactors, with little progress in deploying smaller, innovative designs. Regulatory processes, high costs, and safety concerns have slowed the development of new reactor types. The Trump administration, in 2025, issued an executive order to fast-track reactor development, aiming to demonstrate criticality of new designs by July 4, 2026.
The pilot program included regulatory relaxations and federal support, including partnerships with national laboratories like Los Alamos. Several startups, including Valar Atomics, Antares Nuclear, and Deployable Energy, have benefited from these efforts, reaching criticality at lab sites. These milestones are seen as proof that the industry can move faster if supported by policy and funding.
“These prototypes mean everything and nothing. They do a lot for the companies reaching criticality, but even for those companies, they’re not yet commercial products. They’re test reactors.”
— Adam Stein, Director of the Nuclear Energy Innovation Program at the Breakthrough Institute
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Remaining Challenges for Commercial Deployment
While criticality has been achieved, it remains unclear how quickly these reactors will pass licensing and safety approvals for commercial operation. Supply chain issues, especially for nuclear fuel, and the final regulatory process could still take years. The impact of ongoing regulatory relaxations is also uncertain, as the Nuclear Regulatory Commission (NRC) continues to develop standards for small modular reactors.
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Next Milestones and Regulatory Pathways
The immediate next steps involve completing licensing processes, scaling supply chains for fuel and components, and testing reactors under operational conditions. The Department of Energy and NRC are expected to finalize fast-track licensing pathways, but actual commercial deployment may still be several years away. Monitoring how these reactors perform and how regulators respond will be critical in assessing the future of small nuclear reactors in the US energy landscape.
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Key Questions
What does reaching criticality mean for these reactors?
Reaching criticality indicates that the reactor can sustain a controlled nuclear chain reaction, a key step toward potential power generation. However, it does not mean the reactor is producing electricity or ready for commercial use.
Are these reactors ready to supply power to the grid?
No, these reactors are still prototypes and have not yet been connected to the grid. Further licensing, safety testing, and infrastructure development are required before they can be deployed commercially.
What regulatory changes have been made to speed up reactor development?
The Trump administration relaxed some environmental and safety regulations, including shortening environmental impact statement timelines and streamlining licensing processes. The NRC is also working to develop fast-track approval pathways for these new reactor designs.
What are the main hurdles for commercializing these reactors?
Major hurdles include obtaining final regulatory approval, developing reliable supply chains for fuel and components, and demonstrating economic competitiveness with existing energy sources.
Why is this milestone considered both promising and limited?
It is promising because it shows that new reactor designs can reach criticality faster than before, signaling potential for innovation. However, it is limited because criticality alone does not guarantee commercial viability, and many technical, regulatory, and economic challenges remain.
Source: WIRED
