Oklo’s Groves Isotope Test Reactor achieved first criticality on August 5, 2026, becoming the fifth Department of Energy-authorized reactor to reach this milestone and the first under the DOE’s Reactor Pilot Program to do so on privately owned land in Lockhart, Texas.
The reactor reached criticality—a controlled, self-sustaining nuclear chain reaction—less than a year after groundbreaking, according to Oklo’s announcement. This rapid timeline marks a significant departure from traditional nuclear project development in the United States.
“Reaching criticality in less than a year is an incredible milestone for our team,” said Oklo co-founder and CEO Jacob DeWitte in the company’s statement. “Oklo developed Groves from a greenfield site on private land, completed full-scale civil excavation and construction, manufactured or commercially procured all components, including fuel, and developed its operating programs in-house.”
The Groves achievement comes as part of the DOE Reactor Pilot Program, which set an ambitious July 4, 2026 deadline for at least three reactors to achieve criticality. Four reactors ultimately met or exceeded that target, demonstrating accelerated deployment capabilities across the advanced nuclear sector.
The DOE’s Reactor Pilot Program, established under President Trump’s May 2025 executive order, created a pathway that allowed engineering, construction, commissioning, and operational preparation to advance alongside the DOE’s safety review and authorization process. This integrated approach compressed traditional timelines that typically span years into a months-based schedule, according to the agency and Oklo’s statements.
The Groves reactor is designed as a low-power test facility for isotope production, supporting domestic capabilities for medical, industrial, research, space, and national security applications. The facility establishes operational foundations for Oklo’s broader isotope production strategy and serves as a validation platform for future commercial-scale deployments.
Oklo’s achievement demonstrates that American nuclear deployment timelines can be measured in months rather than years when developers, suppliers, and regulators coordinate on an integrated approach, the company stated. The project generated practical experience in engineering, construction, procurement, reactor operations, startup procedures, and safety readiness that Oklo says will reduce execution risk across its future isotope, powerhouse, and fuel cycle facilities.
Sources
- Oklo Inc. — Official press release announcing Groves reactor first criticality achievement on August 6, 2026
- U.S. Department of Energy — Official announcement and social media posts confirming August 5, 2026 criticality at 9:19 PM EDT in Lockhart, Texas, and noting it as the fifth DOE-authorized reactor to achieve this milestone
- American Nuclear Society — Reporting on criticality achievement and DOE authorization details
- World Nuclear News — Coverage of Oklo’s milestone as part of broader advanced reactor progress in 2026
