Oklo: World’s Only Known Natural Nuclear Reactor Confirmed to be Two Billion Years Old.
OKLO, Gabon – A unique geological phenomenon, the Oklo natural nuclear reactor, remains the only site of its kind discovered globally since its initial finding in 1972. The reactor, located in the Oklo uranium mine in Gabon, West Africa, is estimated to have been active approximately two billion years ago.
The discovery was made by researchers from the French Atomic Energy Commission (CEA) after they noticed a slight but significant depletion of the fissile uranium-235 isotope in ore samples, suggesting the uranium had already undergone fission.
Investigations confirmed that geological conditions at the site—specifically, a sufficiently high concentration of the fissile isotope uranium-235 (around 3.1% at the time) combined with the presence of groundwater acting as a neutron moderator—allowed for a sustained, self-regulating nuclear chain reaction.
Scientists believe the reactor operated in cycles, turning on and off for hundreds of thousands of years. The discovery has provided invaluable data on the long-term behavior of nuclear byproducts in a natural environment, serving as a key case study for the safe disposal of nuclear waste.