In a significant development for US nuclear innovation, four microreactors have achieved zero-power criticality just in time for the nation’s 250th birthday, surpassing the Trump administration’s goal of three by this date.
- Four microreactors hit zero-power criticality ahead of July 4 deadline
- Companies behind reactors founded between 2023 and 2025
- Regulatory and technical hurdles remain before power generation
What happened
Four US microreactors reached the milestone known as zero-power criticality by July 4, a milestone demonstrating the ability to sustain a controlled nuclear chain reaction at minimal power output. This achievement beat the original target set by the Trump administration, which aimed for three microreactors to reach this milestone by the nation’s 250th anniversary.
These reactors are small-scale prototypes selected through the Department of Energy’s Reactor Pilot Program. The initiative supports 11 projects by providing land and assistance from national labs to accelerate development. The companies behind these reactors, including Antares Nuclear, Valar Atomics, Deployable Energy, and Aalo Atomics, were all founded in the past few years, highlighting rapid progress in this emerging sector.
Why it matters
Achieving zero-power criticality is an important early step that validates reactor designs and builds confidence in their technical feasibility. It signals that these microreactors can initiate nuclear chain reactions, a foundational process for power generation, though none are yet producing electricity.
What to watch next
The microreactor companies plan to advance from zero-power criticality to producing electricity, with aggressive timelines that may see small-scale commercial deployments by 2027 or 2028. For example, Aalo Atomics aims to power an on-site data center by 2027, while Deployable Energy targets broader commercial reactor rollouts by 2028.