Oklo's Groves Isotope Test Reactor reached first criticality in Caldwell County, Texas, marking another milestone under the US Department of Energy's Reactor Pilot Program, the company announced. The program, created under an executive order directing the DOE to authorize construction and startup of at least three test reactors by July 4, 2026, has now seen four companies reach criticality within roughly a month of one another: Antares Nuclear, Valar Atomics, Deployable Energy and Aalo Atomics all cleared the same threshold earlier this summer. Oklo co-founder and CEO Jacob DeWitte said reaching criticality in under a year "is an incredible milestone," noting the company built Groves from a greenfield site, procuring or manufacturing every component, including fuel, in-house. The low-power reactor is designed to support future isotope production for cancer care, manufacturing, scientific research, space exploration and national security applications rather than grid electricity.

Separately, California-based Deep Fission received DOE approval of its Nuclear Safety Design Agreement, the first step in the Reactor Pilot Program's authorization pathway, for its Gravity reactor. The design places small modular reactors in boreholes roughly a mile underground, using conventional pressurized water reactor technology and low-enriched uranium fuel. Each unit would generate about 15 megawatts electric, with the company saying a cluster of 100 units could produce 1.5 gigawatts from a fraction of the land required by surface plants. Deep Fission broke ground in December on a pilot project at the Great Plains Industrial Park in Parsons, Kansas, and plans to pursue full Nuclear Regulatory Commission licensing for a commercial version following the demonstration phase. Both developments reflect the accelerating pace of US advanced reactor deployment as the DOE works to expand domestic testing authority outside the national laboratory system.

Source: World Nuclear News - https://world-nuclear-news.org/articles/us-test-reactors-achieve-milestones