---
title: An Isotope Test Reactor in Texas Went Critical Less Than a Year After Groundbreaking
description: Oklo's Groves isotope test reactor near Lockhart is the fifth to go critical under the DOE Reactor Pilot Program, less than a year after groundbreaking.
author: Darie Nani (Editor-in-Chief)
updated: 2026-08-07T21:21:07.857Z
canonical: https://www.sovereignmagazine.com/article/oklo-groves-isotope-test-reactor-first-criticality
image: https://cdn.nanimediahouse.com/oklo-groves-reactor-criticality-119206.webp
categories: Science & Tech
content_type: News
region: United States
publication: Sovereign Magazine
schema_type: Article
---

Oklo Inc. said its Groves Isotope Test Reactor, on private land near Lockhart, Texas, has reached first criticality, achieving a controlled, self-sustaining nuclear chain reaction at low power less than a year after groundbreaking. Groves is the fifth reactor to reach criticality under the Department of Energy's Reactor Pilot Program, a route that lets construction and commissioning proceed alongside the federal safety review rather than waiting for it to finish.

Sam Altman, the OpenAI chief executive, congratulated the company in a post on X on August 7: "congrats to oklo for achieving criticality! (less than a year after groundbreaking)."

## DOE Program Lets Construction and Safety Review Run in Parallel

The program traces to an executive order President Trump signed in May 2025, "Reforming Nuclear Reactor Testing at the Department of Energy," which set a goal of getting at least three test reactors to criticality by [July 4, 2026, using the department's own authorization process](https://www.energy.gov/ne/us-department-energy-reactor-pilot-program) rather than the Nuclear Regulatory Commission's standard licensing track. The department opened applications in June 2025 and closed the initial window that July 21, with later applications accepted on a rolling basis.

Five reactors have now cleared the bar the executive order set. Antares Nuclear's Mark-0 was first to reach criticality, in early June, closely followed by Valar Atomics' Ward 250. Deployable Energy's Unity reactor reached criticality on July 1, and Aalo Atomics' Critical Test Reactor followed in the early hours of July 4. Groves, cleared to start up in late July after a departmental readiness review, is the first of the five built on private land from a greenfield site.

## Oklo Built Groves on Private Land With Private Money

Oklo carried out the civil excavation and construction itself and either manufactured or commercially procured every component, including the fuel, rather than developing custom systems from scratch. It wrote its own startup and operating programs in-house.

"Reaching criticality in less than a year is an incredible milestone for our team," said Jacob DeWitte, Oklo's co-founder and chief executive. "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. Taken together, we believe these accomplishments establish a new benchmark for the Reactor Pilot Program and set the stage for the future of advanced nuclear deployment at scale."

Ted Garrish, the department's assistant secretary for nuclear energy, credited the program's structure for the pace, thanking staff at Oklo, the department and Idaho National Laboratory, which supplied fuel Oklo was awarded for its reactor work. Texas Governor Greg Abbott said the state is "leading America's nuclear renaissance" and that the reactor "will help expand isotope production for critical medical therapies."

## Groves Is a Test Reactor, Not an Isotope Producer

Groves does not make medical isotopes. It is a low-power test reactor, built to show Oklo can design, construct and operate a reactor safely, and to generate the operating experience the company says it needs before building a dedicated isotope production facility. Oklo describes it as part of a wider effort, under its Oklo Isotopes arm, to establish domestic supply for healthcare, industry, research, space exploration and national security.

Molybdenum-99 is used to make technetium-99m, a radiopharmaceutical that goes into more than 40,000 medical procedures a day in the United States, most often to diagnose heart disease and cancer. [Despite accounting for nearly half of global demand, the country has no domestic production and imports its entire supply](https://www.energy.gov/nnsa/articles/nnsa-transitions-american-made-molybdenum-99-effort-doe-office-energy-dominance). Congress directed the department to help close that gap when it passed the American Medical Isotope Production Act in 2012.

Oklo said the engineering, procurement, safety and training work behind Groves will carry into its future isotope, power and fuel-cycle projects. The company is separately [developing fast fission power plants](https://www.sovereignmagazine.com/article/europe-nuclear-revival-too-little-too-late), holds the first Department of Energy site use permit for a commercial advanced fission plant, and has filed the first custom combined license application for an advanced reactor with the Nuclear Regulatory Commission.

## FAQ

**Q: What does it mean when a nuclear reactor reaches criticality?**
Criticality is the point at which a reactor sustains a controlled chain reaction on its own, neither growing nor dying out, at whatever power level it is set to run. Groves reached it at low power, the standard first milestone before startup testing continues.

**Q: What is the DOE Reactor Pilot Program?**
A Department of Energy initiative launched under a May 2025 executive order that lets advanced reactor developers build and prepare a reactor for operation while the department's safety review runs alongside, instead of waiting for it to finish. The stated goal was at least three test reactors reaching criticality by July 4, 2026. Five have now done so.

**Q: Does the Groves reactor generate electricity?**
No. It is a low-power isotope test reactor built to prove out design, construction and operating procedures, not a power plant.

**Q: Why does the United States import medical isotopes?**
The country has no domestic production of molybdenum-99, the isotope used to make the tracer for more than 40,000 medical procedures a day, so hospitals rely on foreign producers. Congress directed the Department of Energy to help establish domestic production in 2012.