The test reactor, near Lockhart in Caldwell County, Texas reached first criticality in August, less than a year after groundbreaking. It is one of 11 advanced reactor projects selected by the US Department of Energy (DOE) in August 2025 for the Nuclear Reactor Pilot Program, a programme aiming to expedite the testing of advanced reactor designs under a DOE authorisation pathway.
The DOE has now cleared the final operations hold point for the reactor - also known as Groves-1 - allowing the facility to advance into its research, testing, and training phase. This will help Oklo prepare the teams and systems needed to support the efficient delivery and operation of future nuclear projects, the company said. Operating experience from Groves-1 will directly inform Groves-2 Forge, Oklo's planned isotope production and processing pilot facility, which is part of the DOE's Nuclear Energy Launch Pad initiative to promote the rapid development and implementation of advanced nuclear technologies by private industry.
With Groves-1 now cleared for unrestricted operations, Oklo said it will test its capabilities relevant to future isotope reactors and the company's fast fission reactor, the Aurora powerhouse.
Groves-1 will serve as a key training and qualification platform for nuclear personnel at future reactor deployments, alongside further equipment testing, including continued evaluations of control rod drive mechanism performance and reliability. It will also enable criticality and reactivity benchmarking operations that support Oklo's isotope production capabilities, its engineering and design models, and potentially light water reactors and the large light water reactor fleet. The company says the resulting data could also help improve fuel performance and power output in small and large light water reactors.
"Taking Groves-1 from greenfield to criticality in less than a year was an important demonstration of what our team can accomplish," Oklo CEO and co-founder Jacob DeWitte said. "Now we're building on that experience by operating the reactor, testing new capabilities, and learning directly from the work. Those lessons can help us develop the people, systems, and processes needed as we advance additional isotope projects and Aurora powerhouses."
"DOE's Reactor Pilot Program reset the nuclear industry's expectations for how quickly we can move from advanced reactor design to demonstration while upholding best-in-class safety standards," Acting Deputy Assistant Secretary for Nuclear Reactors Chimi Zacot said. "Successes like Groves-1's criticality are now paving the way for what comes next."
New reactor designs for commercial use in the USA are reviewed and approved by the US Nuclear Regulatory Commission (NRC), but under the Atomic Energy Act - the fundamental law governing civilian uses of nuclear materials and facilities in the USA - the DOE has the authority to approve reactor authorisations for research, development and demonstration. That authority is now being used to enable advanced reactor developers to certify, build and test prototype reactors that can inform full-scale commercial deployment under the Reactor Pilot Program pathway.
In response to executive orders issued in May 2025 that called for at least three prototype reactors to reach criticality by 4 July 2026, the DOE revamped its authorisation pathway to streamline the process.
In October, the NRC finalised a rule allowing applicants to use relevant analyses, test data and other information from DOE or Department of War (formerly the Department of Defense) reactor demonstration programmes to support commercial reactor licence applications. The rule is designed to make NRC reviews more efficient by allowing the agency to build on existing technical evidence while independently evaluating the safety of proposed commercial projects.