What does achieving criticality in a nuclear reactor mean?

Criticality is the state where a self-sustaining nuclear fission chain reaction begins. However, at this stage, the reactor does not yet generate usable energy but confirms the basic design's functionality.

Which companies are participating in the US DOE program?

The program includes startups Antares Nuclear, Valar Atomics, Deployable Energy, and Aalo Atomics, all developing micro-reactors that are significantly smaller than traditional nuclear power plants.

When are commercial micro-reactors expected to launch?

Companies plan to introduce commercial units by 2027–2028. For instance, Aalo Atomics aims to deploy a 10 MW reactor to power a data center as early as 2027.

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Hardware

Four US Micro-Reactors Achieve Key Milestone in Nuclear Energy Development

July 9, 2026

Photo: MIT Technology Review

Quick answer

Four US startups have achieved criticality in micro-reactors, marking the first step toward commercial nuclear energy systems.

The U.S. Department of Energy has announced a significant milestone in small-scale nuclear energy development. Four startups—Antares Nuclear, Valar Atomics, Deployable Energy, and Aalo Atomics—have successfully tested their micro-reactors, achieving criticality. This means a self-sustaining chain reaction has begun in the units, though they are not yet generating usable energy.

All four companies are part of a pilot program launched by the DOE last August. Under the program, startups gained access to land and support from national laboratories. Unlike traditional nuclear power plants, micro-reactors are compact and could potentially power remote facilities, data centers, or industrial sites.

Despite this success, commercial deployment remains distant. The reactors have only passed the first phase—verifying the feasibility of initiating a chain reaction. To generate electricity, designs must be refined, including adding cooling and heat exchange systems. Experts note that achieving criticality does not guarantee future success, as many technical challenges remain unresolved.

Nevertheless, startups are optimistic. Aalo Atomics has already begun work on a second reactor and plans to deploy a 10 MW unit to power its own data center by 2027. Deployable Energy aims to bring commercial reactors to market by 2028. If these plans succeed, it could mark a breakthrough in decentralized energy.

Common questions

What does achieving criticality in a nuclear reactor mean?: Criticality is the state where a self-sustaining nuclear fission chain reaction begins. However, at this stage, the reactor does not yet generate usable energy but confirms the basic design's functionality.
Which companies are participating in the US DOE program?: The program includes startups Antares Nuclear, Valar Atomics, Deployable Energy, and Aalo Atomics, all developing micro-reactors that are significantly smaller than traditional nuclear power plants.
When are commercial micro-reactors expected to launch?: Companies plan to introduce commercial units by 2027–2028. For instance, Aalo Atomics aims to deploy a 10 MW reactor to power a data center as early as 2027.

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