Austin, Texas-based Aalo Atomics’s test reactor Aalo-X reached zero-power criticality over the weekend, making it the fourth reactor to hit this milestone by the July 4 target deadline.
The Department of Energy said in a Monday press release that Aalo’s sodium-cooled reactor achieved criticality on Saturday morning at its Idaho National Laboratory (INL). Aalo previously broke ground for its test reactor at INL in late August 2025.
The company joins Antares Nuclear’s Mark-0 reactor and Valar Atomics’ Ward 250 reactor under DOE’s reactor pilot program to achieve this goal. President Donald Trump’s Executive Order 14301 set the goal that at least three reactors reach criticality by that deadline.
Additionally, Aalo becomes the fourth non-light water reactor to meet this milestone with Antares, Deployable Energy and Valar Atomics. Deployable Energy was not selected under the reactor pilot program but was selected under DOE’s other program, the Nuclear Energy Launch Pad.
“The hardest problem in nuclear was never the physics, our country simply forgot how to build,” Aalo President and Chief Technology Officer Yasir Arafat said in the release. “The success of the Department of Energy reactor pilot program is proof America can execute again. We are proud to play a major role in America’s nuclear renaissance, going from breaking ground to a sustained chain reaction in just eight months, one of the fastest reactor builds in modern American history.”
“President Trump asked for three advanced reactors to be authorized and achieve criticality by the 250th anniversary of our great country,” Energy Secretary Chris Wright said in the release. “I’m pleased to share that through the dedication and hard work of Aalo, INL and DOE, we have surpassed that ask and delivered four.”
Urenco USA, a U.S. affiliate of the European company Urenco, applauded Aalo for reaching this milestone. Urenco USA said in a Monday press release it worked with DOE to supply various levels of enriched uranium to these advanced test reactors throughout the testing process. Aalo, Antares and Valar Atomics were customers of Urenco’s enriched uranium, according to the release.
“The achievements demonstrated by the U.S. advanced reactor sector this past year are phenomenal and herald an exciting future for the industry,” Magnus Mori, Urenco’s head of advanced fuels, said. “Urenco is working diligently to ensure a robust fuel supply will be available to meet the requirements of our advanced reactor customers once their technologies transition into commercial deployment.”
By reaching criticality at the deadline, Aalo said in a July 4 press release that it has already begun its second reactor for Project Ascension, which will be a commercial-scale system on the Aalo-X site at INL. This new reactor is planned to produce ten megawatts of power for an on-site data center in 2027.
The company plans to hold an event to celebrate its criticality milestone on July 30 in Idaho Falls, Idaho.