First reactor to go critical on private land under the DOE pilot program

Oklo — Groves isotope test reactor, Lockhart, Texas — Oklo's Groves reactor reached first criticality at 9:19 p.m. ET on 5 Aug 2026 — a controlled, self-sustaining chain reaction less than a year after groundbreaking. It is the fifth reactor to go critical under DOE's Reactor Pilot Program and the first to do so on private land, built from scratch on a greenfield site rather than a federal laboratory campus. Groves is a low-power isotope test reactor, not a power plant: it establishes the operating base for commercial isotope production, while Oklo's Aurora power reactors remain a separate track.