US-based Oklo has received Department of Energy (DOE) startup authorisation for its Groves Isotope Test Reactor, clearing the way for fuel loading and first criticality. This marks a milestone in the advanced nuclear sector, establishing the fastest modern timeline from greenfield groundbreaking to regulatory operational approval in just over 10 months. The approval was executed under the federal Reactor Pilot Program (RPP), which aims to significantly accelerate the deployment and testing of advanced nuclear technologies.
The startup authorisation followed a rigorous readiness review, through which DOE confirmed that Oklo had achieved the engineering, organisational, and operational readiness needed to safely receive fuel and begin reactor operations. A multidisciplinary DOE team evaluated whether facility procedures and personnel training were adequate and whether the facility and equipment conformed to the approved design, safety equipment functions properly. It required that safety management programmes had been implemented. Oklo developed these safety management programmes in-house rather than relying on an established or pre-existing operating framework within an established facility such as a national laboratory.
The Groves Isotope Test Reactor was built to secure a domestic supply of medical and industrial isotopes, acting as the immediate pipeline to near-term revenue, paving the way for Oklo’s fast-neutron, liquid-metal-cooled Aurora Powerhouse reactors being developed at the Idaho National Laboratory (INL) site.
Groves is based on a Versatile Isotope Production Reactor (VIPR) system built specifically for harvesting nuclear medicine feedstocks. It features a 15 MWt light-water-cooled, open-pool type design. The reactor core sits submerged at the bottom of a deep, unpressurised pool of water. Because the pool is non-pressurised, it eliminates the thick steel pressure vessels and complex piping used in commercial nuclear plants.
The physical facility was built on private land using commercially procured fuel and components, bypassing traditional national lab constraints. It was engineered for extreme construction speed, completing the primary build phase in just 229 days. Large-scale components were built off-site and transported directly to the Lockhart, Texas footprint, acting as a blueprint for modular deployment.
Earlier in July DOE approved the Documented Safety Analysis (DSA) for the reactor, marking the completion of the project’s final safety documentation process and advances the reactor into its final pre-startup phase. This followed DOE’s approval of the Preliminary Documented Safety Analysis (PDSA), which established the facility’s preliminary safety basis during design and construction.
Groves is a commercial-scale facility, meaning Oklo can repeat the experience with demonstrated experience in siting, building, commissioning, and operating its commercial reactors in the future with confidence in how long it takes and how much it costs to build its isotope production reactors.
“This facility marks the fastest time that we are aware of to go from greenfield to substantial completion for a full-scale, privately funded and sited reactor in history,” said Oklo co-founder and CEO Jacob DeWitte. “By building on a greenfield site on private land, performing full-scale civil excavation and construction, and procuring fuel and all major components commercially, we demonstrated that the advanced nuclear industry can move at a pace that many did not believe possible. And this experience is fully translatable to future commercial deployments.”
Mike Goff, Principal Deputy Assistant Secretary for Nuclear Energy, noted: “The US Department of Energy is excited to see another Reactor Pilot Program participant receive authorisation. With the right enabling environment, Oklo has been able to accelerate their progress and is now ready to take the next step with their technology.”
The Groves VIPR and the Aurora Powerhouse represent two completely distinct engineering philosophies, tailored for entirely separate end-use markets. Oklo is executing a dual-track regulatory strategy. Rather than depending on the lengthy federal pathway, Oklo leveraged DOE authority for pilot deployments on federal land (and specific test sites) while simultaneously advancing broad commercial licensing with the Nuclear Regulatory Commission (NRC).
This followed an initial procedural setback in January 2022 when NRC issued a rare, formal denial of Oklo’s Combined Licence Application (COLA) to build and operate its first Aurora powerhouse at INL due to a lack of technical information. Rather than appealing the decision, Oklo restarted the licensing process in September 2022, shifting to a rigorous “pre-application phase” with NRC. To prevent another comprehensive bottleneck, Oklo began submitting specific technical sections individually. Securing separate, early approvals for these “Topical Reports”, such as its Principal Design Criteria (PDC), allowed the company to iron out regulatory disagreements step-by-step.
The company has achieved several accelerated milestones under updated federal laws such as the ADVANCE Act. NRC officially approved the PDC topical report for the Aurora Powerhouse in May. The PDC serves as the formal “regulatory blueprint” that defines the fundamental safety, reliability, and performance boundaries for the reactor. By locking this in early, Oklo drastically reduced regulatory risk, as the NRC will not need to re-review these core baseline engineering choices during individual plant applications. NRC accepted the final report for review in just 15 days instead of the customary 60 days.
While Oklo broke ground on early infrastructure at INL site under DOE’s site agreements, it continues NRC pre-application engagement to lock in the final operating framework. Oklo is translating the technical data, component classifications, and principal design criteria vetted during its INL regulatory track to move an upcoming commercial project in Ohio into the formal Combined Licence Application (COLA) stage. In this way, Oklo can significantly compress the licensing timeline for its commercial deployments.
Unlike the single 15 MWt test reactor in Texas or the initial Aurora units in Idaho, the Ohio project aims to deliver 1.2 GWe of nuclear energy. In early 2026, Oklo signed a landmark agreement with Meta Platforms to support the technology firm’s regional data centres and massive AI supercluster operations.
Future Oklo projects will build on the established systems, qualified suppliers, and approved operating programmes established through Groves. By establishing a repeatable approach to engineering, construction, commissioning, operations, and regulatory authorisation, Groves helps reduce execution risk and accelerate future deployments across all of Oklo’s business units. The RRP created a rigorous pathway that enabled construction and organisational readiness activities to proceed while DOE conducted its reviews. Groves demonstrates how that approach can support advanced reactor deployment while maintaining a focus on safety.
