On June 4th, Antares Nuclear’s Mark-0 microreactor reached criticality at Idaho National Laboratory. It’s the 53rd reactor built at the research site and the first under the Department of Energy’s (DOE) Reactor Pilot Program. The department is targeting at least three advanced-reactor criticalities by America’s 250th birthday celebration on July 4th, 2026.
Criticality is a milestone for an advanced nuclear design. A reactor is critical when its fission chain reaction sustains itself, each round of neutrons splitting enough atoms to trigger the next without an outside source driving it. Antares’ reactor does not use the light-water design that the U.S. has successfully licensed for decades, so a criticality test ensures that the new technology behaves as predicted and can be shut down safely.
There’s no better time for the U.S. to be pursuing innovative nuclear designs. American electricity demand is climbing for the first time in a generation, driven by data centers, artificial intelligence (AI), and new manufacturing. Data center load alone is projected to roughly double, from 31 gigawatts (GW) in 2025 to 66 GW by 2027. Small modular reactors and microreactors, small enough to place next to a data center or a factory, are an excellent option that can deliver round-the-clock power.
While a technical feat, producing electricity and reaching commercial viability is a different beast. Antares plans to test an electricity-producing version of the reactor in 2027 under DOE authority and target its first deployment at Joint Base San Antonio in 2028 through the Air Force’s Advanced Nuclear Power for Installations program.
Reaching commercial viability will mean getting licensing under the Nuclear Regulatory Commission (NRC), which is the real bottleneck. Under the licensing framework the NRC has used since 1989, only two new reactors have reached commercial operation: Vogtle Units 3 and 4 in Georgia in 2023 and 2024, respectively.
Reforms are already in place to speed the NRC’s licensing process without compromising safety. The bipartisan ADVANCE Act of 2024 ordered the NRC to expedite reviews, cut advanced-reactor fees, and write microreactor guidance. Executive Order 14300 imposed deadlines that the agency had never faced: final decisions on new reactor applications within 18 months. On April 29, 2026, the NRC’s Part 53 framework took effect, the first new licensing pathway in decades, risk-informed rather than built around 1970s light-water plants. The NRC has also proposed a faster track for designs already proven under DOE or military authorization, the bridge from a test reactor to a salable one.
Antares can prove its reactor and field its first units on federal ground with the NRC barely involved. Whether the technology ever reaches a commercial data center or an American home depends on the regulatory roadblocks thrown up in Antares’ way. But DOE’s streamlining of the process only bodes well for America’s nuclear power comeback.