Oklo's Groves Isotope Test Reactor achieved criticality Wednesday evening at the company's site in Lockhart, Texas, becoming the fifth reactor authorized by the Department of Energy to reach that milestone under the agency's Reactor Pilot Program. Criticality was reached at 9:19 p.m. Eastern time, according to the DOE.
"Reaching criticality in less than a year is an incredible milestone for our team," said Oklo cofounder and CEO Jacob DeWitte. The company said it developed Groves from a greenfield site on private land, completing civil construction, procuring components and fuel, and building its operating programs largely in-house.
Executive Order 14301 set a goal of at least three DOE-authorized test reactors reaching criticality by July 4. Antares and Valar Atomics, both participants in the Reactor Pilot Program, reached criticality in June. Deployable Energy, part of the DOE's Nuclear Energy Launch Pad, followed in early July, and Aalo Atomics reached criticality on July 4 itself.
Groves is a 15-megawatt thermal, pool-type, water-cooled reactor built by Oklo Isotopes, a subsidiary Oklo formed after acquiring radioisotope producer Atomic Alchemy in 2025. It is the first DOE-authorized reactor to reach criticality on private land rather than a national laboratory or state-owned site. Oklo, based in Santa Clara, California, also has two other reactor projects underway, including the 75-megawatt Aurora Powerhouse.
Texas Governor Greg Abbott welcomed the milestone, crediting it with strengthening the state's nuclear workforce and domestic supply chains.
Source: Nuclear Newswire (American Nuclear Society) - https://www.ans.org/news/2026-08-06/article-8277/oklos-isotope-test-reactor-achieves-criticality/