Oklo's Groves Isotope Test Reactor has achieved first criticality, the company announced. The milestone marks a significant step for the private nuclear sector, which has long promised faster, cheaper reactor development but often struggled to deliver.
What the reactor is
The Groves reactor is a test facility designed to produce medical and industrial isotopes. It uses a compact, liquid-metal-cooled design that Oklo says can be built and licensed more quickly than traditional large-scale reactors. First criticality means the reactor sustained a controlled nuclear chain reaction for the first time — a basic but essential step toward full operation.
If the reactor moves into commercial service, it could shorten the timeline for new nuclear projects. Investors have been cautious about advanced reactor startups, and a working test reactor could help change that. The project also aims to reduce U.S. dependence on foreign isotope supplies, which are currently imported from aging reactors abroad.
Oklo's success comes as the nuclear industry faces renewed interest from governments and tech companies seeking carbon-free power. But many advanced reactor designs remain on paper or in early testing. The Groves reactor's criticality is a concrete achievement that could boost confidence in the sector.
The company will now work toward full-power operation and isotope production. Regulatory approvals from the Nuclear Regulatory Commission will be needed before the reactor can operate at higher power levels. Oklo has not announced a specific timeline for those next steps.
