The nuclear energy industry just hit a historic milestone that could reshape how artificial intelligence gets its power. On June 4, 2026, Antares Nuclear's Mark-0 reactor became the first new reactor design to achieve criticality, or sustained nuclear chain reaction, in the United States since 1973. Three other novel reactor designs have since met the same milestone, with up to four more expected by year's end. These aren't the massive cooling-tower reactors of decades past; they're shipping-container-sized machines designed to be mass-produced, portable, and scalable enough to fit in a pickup truck bed.

The timing is no accident. Data centers powering artificial intelligence consume staggering amounts of electricity, and the U.S. power grid is struggling to keep up. The convergence of rare bipartisan political support, decades of stalled nuclear innovation, and skyrocketing electricity demand from AI and quantum computing has created a perfect storm of opportunity for next-generation nuclear technology.

What Makes These New Reactors Different from Traditional Nuclear Plants?

The reactors achieving criticality in 2026 share fundamental design principles that set them apart from conventional nuclear infrastructure. Unlike traditional reactors that require massive concrete containment structures and external cooling systems, these new designs are engineered for portability, safety, and rapid deployment. Antares Nuclear's Mark-0, for example, uses sodium heat pipes for cooling without requiring external power, and it could produce up to 20 megawatts of electricity, enough to power approximately 15,000 homes, by 2027.

Valar Atomics' Ward 250 reactor, which achieved criticality on June 18 at the San Rafael Energy Lab in Utah, represents another design philosophy. This 75-foot-long, 15-foot-wide micro-reactor uses helium cooling and TRISO uranium fuel, a specially designed fuel that prevents radioactive release even in worst-case scenarios. The Ward 250 can generate up to five megawatts of electricity, enough for approximately 5,000 homes, and can be transported by truck, train, or plane. Because of its fuel design, it requires no large cement containment structures, making it fundamentally different from reactors built in the 20th century.

How Are These Reactors Being Developed and Tested?

• Government Support: Ten companies, including Antares Nuclear, were selected by the Department of Energy in August 2025 to develop "first mover" innovations under a reactor pilot program authorized by President Donald Trump. The program aims to license 10 new reactors by 2030 and quadruple the nation's nuclear energy capacity by 2050.
• Testing Infrastructure: Developers gain access to the Idaho National Laboratory, an 890-square-mile facility in the Arco Desert where atomic power was first used to generate electricity in 1951. The Materials and Fuels Complex, located 40 minutes from the lab's administrative offices, serves as the primary testing ground for prototype reactors.
• Accelerated Timelines: Energy Secretary Chris Wright stated that new reactors could be available for commercial sale within six months to a year, thanks to executive orders that overhaul the Nuclear Regulatory Commission and streamline approvals.
• Military and Space Applications: Antares Nuclear is under contract to deliver micro-reactors to the U.S. Air Force's Joint Base San Antonio in 2027 and to the U.S. Army by September 2028. The company is also testing a 100-kilowatt reactor at NASA's Marshall Space Flight Center for potential use in space travel and as a moon base power plant.

Why Does This Matter for AI and Data Centers?

The electricity demand from artificial intelligence is growing exponentially. The U.S. is projected to see a 25 percent increase in electricity demand by 2030 and more than 70 percent increase by 2050, driven largely by data centers and AI infrastructure. Traditional power sources, including existing nuclear plants and renewable energy, cannot keep pace with this surge. The United States currently maintains 96 reactors across 28 states that produce nearly 20 percent of the nation's electricity, but since 1990, only two new reactors have been built while 18 have been retired.

Portable micro-reactors could solve this bottleneck by allowing hyperscalers and tech companies to deploy power generation directly at data center sites. Valar Atomics demonstrated this potential on July 1 when it used the Ward 250 reactor to briefly power a website hosted on an Nvidia Blackwell AI chip, proving that next-generation nuclear power can directly support AI infrastructure.

"I got emotional, emotional, today to see the humans, the reactors, the steel, the action that's happening at the lab site. To think on June 4, less than 13 months after Trump's executive orders, that reactor ran critical because a three-year-old company said, 'Yes, we can. Yes, we will,' and leaned in," said Energy Secretary Chris Wright.

Chris Wright, Energy Secretary

What's the Timeline for Commercial Deployment?

Antares Nuclear's roadmap illustrates how quickly these reactors could move from prototype to deployment. The company, founded in 2023 and backed by more than $140 million in private financing, achieved its 2026 goal of securing Mark-0 criticality. The company is now shifting focus to its Mark-1 electricity-producing reactor, which will be tested in 2027, with plans to deploy reactors on customer sites by 2028.

The Mark-0 prototype is fueled by high-assay low-enriched uranium and housed in a 26-foot-deep, 26-foot-wide chamber with 11 cement slabs collectively weighing more than 200 tons for shielding. This design demonstrates that safety and containment can be achieved in compact form factors, addressing one of the historical concerns about nuclear power.

Beyond Antares, other companies are advancing rapidly. Aalo Atomics and Valar Atomics have also achieved criticality under the pilot program, while Deployable Energy did so as a participant in the Department of Energy's newly established nuclear launchpad program. Micro-reactors from Radiant Industries, Natura Resources, Last Energy, Atomic Alchemy, Deep Fission, and Oklo are on the "cusp" of criticality at the national lab and elsewhere.

What Regulatory Changes Made This Possible?

The acceleration of nuclear development is rooted in regulatory reform. President Trump's executive orders in May 2025 called for licensing 10 new reactors by 2030 and quadrupling nuclear capacity by 2050. These orders also overhauled the Nuclear Regulatory Commission to streamline approvals. Additionally, Congress adopted the ADVANCE Act in 2024, which deregulates and subsidizes the nuclear industry to meet projected electricity demand increases.

Criticality is generally the first step toward Nuclear Regulatory Commission licensing for commercial reactor production and sale. The fact that four reactors have achieved this milestone in a single year, with more expected before 2026 ends, suggests that the regulatory and financial barriers that stalled nuclear development for decades are finally crumbling.

The convergence of AI's insatiable power appetite, political consensus on nuclear energy, and breakthrough reactor designs creates a rare moment in energy history. Within 18 to 24 months, portable nuclear reactors could begin powering the data centers that train the next generation of artificial intelligence models, fundamentally changing how the tech industry solves its energy crisis.