Oklo's Groves reactor reaches criticality, testing a faster path to isotope production
The Texas reactor went from groundbreaking to a sustained chain reaction in under a year, though its authorized power is capped at 100 watts.
By Ryan Merket · Published
Why it matters
Groves gives Oklo operating experience and a completed private-site reactor, but its 100-watt limit leaves commercial isotope output and power generation unproven.
Oklo said on August 6th that its Groves Isotope Test Reactor in Texas had reached first criticality, giving co-founder and CEO Jacob DeWitte (@jakedewitte) a working test of the accelerated construction and authorization process he wants to reuse across the nuclear developer's projects.
The milestone means Groves sustained a controlled nuclear chain reaction at low power. It came less than a year after groundbreaking and two weeks after the Department of Energy granted startup authorization on July 23rd, allowing Oklo to load fuel and begin reactor operations.
DeWitte, who has worked on sodium fast reactors, molten salt reactors and nuclear fuel-cycle technology, founded Oklo in 2013 with COO Caroline DeWitte (@caorilne). Both founders trained as nuclear engineers at MIT. Jacob DeWitte also earned a doctorate there, while Caroline DeWitte entered the program after studying mechanical engineering and economics at the University of Oklahoma.
Groves gives them a completed reactor project on private land near Lockhart, Texas, rather than another design, permit application or construction plan. Oklo said it developed the greenfield site, completed civil construction, sourced or manufactured the reactor's components and fuel, created operating procedures, and trained personnel in-house.
That execution record is the commercial value of Groves. The reactor itself is a limited test facility, not an operating isotope factory or power plant. A DOE environmental review describes Groves as a zero-power critical assembly with a maximum power level of 100 watts. The document says its operating phase is scheduled to end by the close of 2026.
Oklo calls the facility commercially representative because its physical construction, suppliers, fuel procurement and operating organization are intended to resemble the systems needed for later plants. First criticality validates that the reactor core can sustain fission and that Oklo navigated the DOE authorization process. It does not establish isotope output, production economics or the performance of a commercial generating reactor.
An acquired isotope business gets its first reactor
Groves originated inside Atomic Alchemy, the radioisotope developer Oklo acquired in February 2025. An Oklo regulatory filing valued the transaction at about $28.4 million, including roughly $1 million in cash and $27.4 million in stock. Atomic Alchemy generated no revenue during 2025, according to the filing.
The acquisition gave Oklo a second potential business alongside its planned Aurora powerhouses. Radioisotopes are used in medical diagnosis and treatment, manufacturing, research, space systems and defense. Oklo plans to use experience from Groves to develop larger facilities capable of producing those materials domestically.
The near-term work is operational. Oklo said Groves has created procedures and staff experience spanning reactor startup, safety readiness, commissioning, procurement and operator qualification. Those capabilities take time to build and are difficult to demonstrate through engineering documents alone.
The isotope strategy also gives Oklo a deployment test that is separate from Aurora, the fast-reactor system at the center of its electricity business. Groves is a low-power, water-cooled test reactor, while Aurora is being developed as a liquid-metal-cooled power reactor. Lessons involving project management, suppliers and regulatory reviews may transfer between the programs; reactor performance does not transfer directly between the two designs.
The DOE pathway moved reviews alongside construction
Groves proceeded through the DOE Reactor Pilot Program, created after a May 23rd, 2025 executive order directed the department to accelerate advanced reactor testing. The program allowed engineering, construction and operational preparation to advance while DOE conducted safety reviews.
The administration set a goal of having at least three advanced reactor concepts outside national laboratories reach criticality by July 4th, 2026. DOE said four other projects met that deadline. Oklo had separately targeted July for Groves, then announced criticality on August 6th.
Groves still marks a distinct test of the program because Oklo built it from an undeveloped, privately owned site rather than installing the experiment inside an existing national laboratory. Oklo described Groves as the first Reactor Pilot Program project to reach criticality under those conditions. DOE previously identified the facility as a project outside the national laboratories and completed its environmental review in June.
For the DeWittes, the result supplies evidence for a thesis Oklo has pursued since 2013: nuclear schedules can be compressed by developing the plant, operating model and regulatory record together. Groves proves that approach can produce a low-power critical reactor quickly. Oklo's remaining task is translating that speed into licensed facilities that sell isotopes or electricity at commercial scale.