Oklo’s Isotope Test Reactor achieves criticality
Oklo’s Groves Isotope Test Reactor became the fifth Department of Energy–authorized reactor to achieve criticality under the agency’s authorization process, it was announced earlier today.
Criticality was reached at 9:19 p.m. (EDT) on Wednesday at the company’s Groves facility in Lockhart, Texas, according to the DOE.
“Reaching criticality in less than a year is an incredible milestone for our team,” Oklo cofounder and CEO Jacob DeWitte said in an announcement. “Oklo developed Groves from a greenfield site on private land; completed full-scale civil excavation and construction; manufactured or commercially procured all components, including fuel; and developed its operating programs in-house. Taken together, we believe these accomplishments establish a new benchmark for the Reactor Pilot Program [RPP] and set the stage for the future of advanced nuclear deployment at scale.”
Path to criticality: Executive Order 14301 set an ambitious goal for at least three test reactors to achieve criticality by July 4. Two private companies participating in the DOE’s RPP—Antares and Valar Atomics—reached this stage in June. Deployable Energy, which is participating in DOE’s Nuclear Energy Launch Pad, became the third at the start of July. Aalo Atomics, another RPP participant, achieved criticality in the early hours of July 4.
The 15-MWt pool-type, water-cooled, nonpressurized Groves Isotope Test Reactor is a project of Oklo Isotopes, the name of the company formed after Oklo acquired radioisotope production company Atomic Alchemy in 2025.
The Santa Clara, Calif.,–based Oklo has two other reactor projects in the works: the 75-MWe liquid metal–cooled, metal-fueled Aurora Powerhouse and the plutonium-fueled Pluto reactor.
The Groves Isotope test reactor is the first reactor under DOE authorization to achieve criticality on private land—in this case, on a greenfield site. Aalo’s, Antares’s, and Deployable’s reactors are sited at Idaho National Laboratory, while Valar Atomics has its reactor at the state-owned Utah San Rafael Energy Lab.
Groves is part of Oklo Isotopes’ long-term plans to build domestic isotope production facilities to benefit health care, industry, research, space, and national security. Oklo has described Groves as a test platform for future production-scale deployments of these types of isotope production reactors. In its announcement, Oklo said the work done at Groves has provided valuable experiences in areas like “project engineering, construction, procurement, reactor operations, startup procedures, safety readiness, training, qualification work, and deployment execution that can inform future isotope production facilities.” The experience will also prove valuable in Oklo’s future isotope, Powerhouse, and fuel cycle facilities.
Texas Gov. Greg Abbott welcomed the news out of Lockhart, a city just south of Austin.
“From expanding our nuclear workforce to rebuilding critical domestic supply chains, Texas is creating the foundation for the next generation of advanced nuclear development. Congratulations to Oklo on reaching this important milestone, which will help expand isotope production for critical medical therapies and reinforce Texas’s leadership in nuclear innovation,” Abbott said in a statement.
