Nuclear Power at Startup Speed: A Reactor Milestone in Under 12 Months

IDAHO FALLS, ID – June 04, 2026 – In a development that signals a dramatic acceleration in American energy innovation, the nuclear startup Antares today announced it has achieved initial criticality with its Mark-0 microreactor. The event, which took place at Idaho National Laboratory (INL), marks the first time in over four decades that a privately developed, non-light-water reactor has reached this milestone in the United States. More remarkably, the company went from concept to a functioning, critical reactor in less than a year, a timeline unheard of in an industry historically defined by decade-long projects.

This achievement makes Antares the first company to succeed under the U.S. Department of Energy's (DOE) ambitious Reactor Pilot Program, a new initiative designed to shatter old paradigms of nuclear development. Achieving criticality means the reactor's core can sustain a controlled, chain nuclear reaction—the fundamental process of a nuclear reactor. While the Mark-0 is a zero-power test unit designed to validate physics models rather than produce electricity, its success is a powerful proof of concept for both the technology and the novel regulatory pathway that enabled it.

“Today’s achievement is a historic moment for American nuclear energy,” said U.S. Energy Secretary Chris Wright. “By bringing the first American non-light water privately developed reactor to criticality in more than four decades, Antares has shown what is possible when American innovation is unleashed.”

A New Blueprint for Nuclear Innovation

The speed of Antares' achievement is the central story. The company's CEO, Jordan Bramble, has been vocal about breaking the industry's reputation for over-promising and under-delivering. "Hitting our commitments is everything to us. Nuclear in America has been defined for too long by delays, by companies that said they would and then didn't," Bramble stated. "We said criticality in 2026, electricity production in 2027, and power to the warfighter in 2028. Today is the first of those commitments delivered on the schedule we set."

This new pace is made possible by a convergence of factors, chief among them the DOE Reactor Pilot Program. Established by a 2025 executive order, the program allows companies to test their designs under DOE authorization at national lab sites, bypassing the traditionally lengthy Nuclear Regulatory Commission (NRC) licensing process for these initial demonstration phases. This creates a regulatory sandbox where innovation can happen iteratively and quickly, generating real-world data that can then be used to inform a future commercial license application.

"We went from concept to a critical reactor, safely, in less than 12 months," Bramble added. "That doesn't happen by accident... It forced us to build an organization that can design, license, build, and test reactors on a schedule, and it forced DOE's licensing pathway to run at the pace the country needs."

The collaboration between Antares, the DOE, Idaho National Laboratory, and the fuel supplier BWX Technologies, Inc. (BWXT) serves as a new model for public-private partnership. This approach not only accelerates development but also establishes a replicable pathway that other advanced reactor companies can follow, potentially ushering in a wave of innovation across the sector.

Powering America's Defense

Beyond its implications for the commercial energy sector, the Antares test is a critical step forward for U.S. national security. The demonstration was conducted with integration and observation support from the U.S. Army, a key future customer for this technology. The data gathered from the Mark-0 reactor directly supports the Department of War's Project Pele, an initiative to design and build a prototype of a mobile microreactor for military use.

For the modern military, energy is a significant vulnerability. Forward operating bases and domestic installations rely on vulnerable supply chains for diesel fuel, creating logistical burdens and security risks. Compact, reliable microreactors that can operate for years without refueling represent a game-changing solution, promising energy resilience and independence. "Next, we need to see a reactor generate electricity at full power," said Dr. Jeff Waksman, a senior Army official for energy and environment. "Then the Army will take the baton and deliver a full electricity-generating nuclear reactor to a military installation."

The technological backbone of this security vision is the TRi-structural ISOtropic (TRISO) particle fuel, fabricated for Antares by Virginia-based BWXT. Each poppyseed-sized kernel of uranium fuel is encased in multiple ceramic layers, making it exceptionally robust and capable of withstanding extreme temperatures. This “meltdown-proof” design is a cornerstone of modern reactor safety.

“BWXT is proud to work with Antares and deliver the fuel necessary for this important milestone,” said Joe Miller, a president at BWXT. He noted that the fuel expertise matured through Project Pele directly underpinned Antares’ success, demonstrating a synergistic loop where government defense projects enable and de-risk commercial innovation, which in turn feeds back into military capability.

The Policy Engine of a Nuclear Revival

This rapid breakthrough didn't happen in a vacuum. It is the direct result of a concerted, multi-year policy push from Washington to revive the nation's nuclear industry. The groundwork was laid by the bipartisan ADVANCE Act, signed into law in 2024, which directed the NRC to modernize its licensing processes for advanced reactors. This culminated in the new Part 53 rule, a flexible, risk-informed framework that became effective in April 2026.

More pointedly, a series of executive orders signed in May 2025 by the Trump administration lit the fuse for this accelerated development. Executive Order 14301 specifically created the DOE Reactor Pilot Program and set the ambitious goal of achieving criticality in at least three advanced reactors by America's 250th birthday on July 4, 2026. Antares is the first to cross that finish line.

This combination of legislative action and executive directive reflects a growing consensus that nuclear energy is critical for achieving clean energy goals, ensuring grid stability, and maintaining U.S. technological leadership. By creating fast-track programs and demanding results on commercial timelines, policymakers are actively cultivating a more dynamic and competitive nuclear landscape.

For Antares, a startup founded only in 2023 and backed by over $140 million in funding, criticality is just the first step. The company plans to use the same facility and TRISO fuel to build its electricity-producing Mark-1 reactor, aiming for power generation in 2027 and deployment to military installations by 2028. The data from this zero-power test provides invaluable, real-world validation of their reactor physics, control systems, and supply chain maturity. These lessons, learned at an unprecedented pace, will have compounding benefits across every reactor Antares builds, shaping the trajectory of America's nuclear ambitions for years to come.