The U.S. Department of Energy (DOE) has announced that Aalo Atomics has successfully achieved advanced reactor criticality with its Aalo-X test reactor at Idaho National Laboratory, marking another milestone for the country’s next-generation nuclear energy programme.
The zero-power-fuelled criticality demonstration was completed under the DOE’s Reactor Pilot Program, making Aalo-X the fourth DOE-authorised advanced reactor design to reach criticality.
The achievement also exceeds the federal target established in President Donald Trump’s May 2025 executive order, which called for three advanced reactors to achieve criticality by the July 4 deadline.
The result highlights the accelerating pace of advanced nuclear development in the United States, reinforcing the Reactor Pilot Program as a key pathway for demonstrating new reactor technologies while supporting broader efforts to expand domestic nuclear energy capacity.
Aalo-X strengthens momentum for advanced reactor criticality
The successful test adds Aalo-X to a growing list of advanced reactor projects that have recently reached the same milestone through the DOE programme.
During June, Antares Nuclear’s Mark-0 reactor, Valar Atomics’ Ward 250 reactor and Deployable Energy’s Unity reactor each completed criticality demonstrations.
Reaching criticality confirms that a reactor can sustain a controlled nuclear chain reaction, representing one of the most important technical milestones before further testing and development can continue.
The DOE said the latest achievement demonstrates increasing momentum across the Nuclear Energy Launch Pad initiative, which aims to accelerate the deployment of innovative reactor technologies by streamlining demonstration and regulatory processes.
Reactor Pilot Program accelerates nuclear innovation
The Reactor Pilot Program was established to help first-of-a-kind advanced reactor designs move more rapidly from concept to demonstration.
Rather than following traditional licensing timelines, the programme enables DOE-authorised projects to validate new reactor technologies under an accelerated framework.
Aalo Atomics also highlighted the rapid pace of the Aalo-X project, progressing from construction to a sustained chain reaction in just eight months. The company described the timeline as one of the fastest modern reactor development programmes in the United States.
The latest success suggests that advanced reactor developers are increasingly able to shorten demonstration schedules while maintaining technical milestones required for future commercial deployment.
Growing confidence in the US nuclear sector
With four reactors now achieving advanced reactor criticality, the DOE’s pilot programme has exceeded the original federal objective and strengthened confidence in the viability of next-generation nuclear technologies.
The milestone also reflects broader efforts to modernise nuclear development in the United States through regulatory reform and faster demonstration pathways.
As additional reactor concepts progress through the initiative, the DOE expects the Reactor Pilot Program to continue supporting innovation, helping advanced nuclear technologies move closer to commercial deployment while contributing to long-term energy security and expanded clean electricity generation.
