Three small-scale nuclear reactors have reached criticality in the United States within the past month, a milestone that signals a potential shift in how the nation's largest power consumers may source electricity. The reactors, built by three separate companies, are part of a Department of Energy program designed to accelerate advanced nuclear demonstrations.

What You Need to Know

Three advanced microreactors have achieved a sustained nuclear chain reaction, a key step toward commercial operation. The Department of Energy is funding these demonstrations to prove that small reactors can be deployed faster and cheaper than traditional nuclear plants. Data centers, which face growing energy demands, are evaluating microreactors as a possible 24/7 carbon-free power source. Each reactor uses different technology but all aim to fit within the footprint of a shipping container.

A Milestone for Advanced Nuclear

The three reactors that reached criticality include Unity, built by Houston-based Deployable Energy, and two others developed by Torrance-based Antares and El Segundo-based Valar Atomics. All three cleared the same technical hurdle in June and early July. Criticality means the reactor has achieved a self-sustaining fission reaction, a prerequisite for generating heat that can be converted into electricity.

  • Deployable Energy's Unity: Designed to produce 1.5 megawatts of thermal power, using a novel high-temperature gas-cooled design.
  • Antares reactor: A molten-salt cooled microreactor targeting 5 megawatts of electrical output.
  • Valar Atomics reactor: A heat-pipe cooled system that can be factory assembled and trucked to a site.

Why Data Centers Are Paying Attention

The timing aligns with a surge in electricity demand from data centers, driven by AI workloads and cloud computing. Hyperscale operators have been searching for reliable, carbon-free power sources that can run around the clock. Microreactors, which are smaller than conventional nuclear plants and can be sited near load centers, offer a potential alternative to grid delays and natural gas.

Major technology companies have already signed power purchase agreements with nuclear developers. The criticality achievements in this DOE program, however, represent the first time multiple advanced reactors have operated simultaneously on U.S. soil. The demonstrations will provide real-world data on safety, cost and operational reliability that data center planners need before making large commitments.

What's Next for Microreactor Deployment

The three reactors will now undergo testing at the Idaho National Laboratory and other DOE sites. Each must demonstrate sustained operation, load-following capability and safety shutdown procedures before receiving a license from the Nuclear Regulatory Commission. Commercial deployment could begin as early as 2028 if the demonstrations succeed.

Developers still face challenges including fuel supply, regulatory timelines and public acceptance. The DOE program, however, has compressed development cycles by providing test infrastructure and streamlined oversight. Investors and utilities are watching the outcome closely as a potential blueprint for scaling microreactor production.

Why This Matters

The success of these three microreactors could reshape how energy-intensive industries power their operations. Data center operators face mounting pressure to reduce carbon emissions while meeting exponential growth in electricity consumption. If microreactors prove viable, they could bypass the decade-long construction timelines of traditional nuclear plants and the intermittency of solar and wind. The Department of Energy's demonstrations are a critical test of whether advanced nuclear can deliver on its promise of clean, dispatchable power at a scale that matters for the digital economy.