A 1 megawatt class research reactor on 30 acres of Texas rangeland reached first criticality in under a year, which engineers say is the fastest privately sited reactor startup on American soil in decades
Eleven months ago, the ground outside Lockhart, Texas held nothing but caliche dust and scrub grass.
No building, no foundation, no fuel assemblies.
Engineers broke ground, poured concrete, assembled the core, and ran a commissioning checklist longer than most airport safety manuals.
Readers tracking the broader industrial buildup will find parallel context in SMR control orders, another front that Lockhart now anchors at the reactor level.
On August 5, 2026, the Groves research reactor held its first controlled nuclear chain reaction at low power.
What made that possible so fast, and what does it cost to prove?
What a chain reaction requires, and why bare private land made it harder
Criticality is the moment a reactor becomes truly self sustaining: each uranium atom that splits releases neutrons, and enough of those neutrons strike other atoms to keep the reaction going without any external nudge. The physics has to be exactly right, which means fuel loading, core geometry, and moderating material must all be sized and positioned with precision.
What made Lockhart unusual was not the physics but the address. Groves is the first reactor under the federal program to achieve criticality on private land, built from the ground up on a greenfield site. Every reactor that had gone critical before it under the federal fast track program did so on national laboratory land, where decades of infrastructure, security perimeters, and regulatory history already existed.
Lockhart had none of that. The team had to build the regulatory framework alongside the physical building, simultaneously rather than sequentially, which compressed a process that had historically stretched across years into something closer to a sprint.
What the site looks like and what went into it
Lockhart sits about thirty miles south of Austin in Caldwell County, better known to Texans for barbecue than for energy infrastructure. The reactor design is a pool type, meaning the core sits submerged in a tank of water that simultaneously cools it and shields the room outside from radiation, a well understood configuration that strips away a layer of engineering complexity.
The Groves reactor was built as a pilot scale test platform, not a power plant. The goal was isotope production: the reactor’s neutron flux will eventually manufacture medical and industrial isotopes rather than spin a turbine. But before any commercial activity could begin, the core had to prove it could sustain a chain reaction at all.
That proof arrived in the first week of August, following authorization through the DOE Reactor Pilot Program, an accelerated federal initiative to fast-track the testing and demonstration of advanced nuclear reactor designs.
The record and where it comes from
The company claims Groves may be the fastest privately funded, privately sited reactor build in American history, tied to an under eleven month construction timeline. That claim is difficult to verify against every reactor ever built in the United States, but context gives it weight. The nuclear industry’s modern reputation was shaped by projects that ran years past schedule and billions over budget.
Two private companies participating in the DOE’s Reactor Pilot Program, Antares and Valar Atomics, reached criticality in June, with a third following at the start of July and a fourth in the early hours of July 4. Groves took slightly longer but carried a heavier burden: building from scratch on bare private land with no national laboratory scaffolding to lean on.
Criticality was reached at 9:19 p.m. Eastern time on August 5 at the Lockhart facility. “Reaching criticality in less than a year is an incredible milestone for our team,” co-founder and chief executive Jacob DeWitte said. Groves became the fifth Department of Energy authorized reactor to achieve criticality under the agency’s authorization process.
The catch and what the reactor still cannot do
First criticality is a gate, not a finish line. Groves is a low power test reactor, and this milestone is not grid connection, commercial power operation, or proof that isotope production has begun. The reactor will spend the months ahead accumulating operating hours and demonstrating that its systems behave as the safety analysis predicted.
That institutional knowledge is arguably worth more than the megawatts, which for now stand at zero. The project has generated practical experience in project engineering, construction, procurement, reactor operations, startup procedures, safety readiness, training, qualification work, and deployment execution that can inform future isotope production facilities. Readers tracking the broader industrial buildup will find parallel context in SMR control orders, another front that Lockhart now anchors at the reactor level.
There is also a financial dimension worth noting plainly. The company reported a net loss of $81.6 million for the quarter and an operating loss of $124.2 million, reflecting the reality that it remains unprofitable as it builds toward commercial scale. Speed on the engineering side has not yet translated into revenue.
What it means for the places that come next
The project is generating data, experience, and capabilities to inform future commercial scale isotope production facilities. Isotopes from research reactors are indispensable to medical imaging and cancer treatment: technetium-99m alone is used in roughly forty million diagnostic procedures a year worldwide, and most of it depends on reactor produced molybdenum.
A domestic supply chain anchored on privately owned reactors would reduce the country’s exposure to the aging foreign reactors that currently dominate that market. That is a structural change, not a record breaking favor to a single company. The federal effort to expand advanced reactor supply chains, including the domestic fuel push, will eventually need operating reactors to consume what that chain produces.
The American Nuclear Society’s Nuclear Newswire coverage of the milestone noted that the program’s executive order had set a target of at least three reactors reaching criticality by July 4, a bar that was not only met but exceeded, with Groves as the fifth to cross it. The program target becoming a floor rather than a ceiling is the detail that matters most to anyone planning the next build.
Groves is still a test reactor at low power in a county that smells of mesquite smoke, and commercial isotope production remains ahead of it. But the chain reaction that held in Lockhart this August was real, it was recorded, and the empty rangeland that preceded it will not look that way again.
Hugo is an engineer with strong technical expertise. Multilingual from an early age, his writing combines technical clarity with a strong interest in science and energy.
