The nuclear reactor worked in the same way as modern reactors and was completely natural. It was discovered in 1972 in Oklo, Gabon.
Long before Humanity’s search for nuclear energy, the Earth itself was home to a natural nuclear reactor. Discovered in 1972 by a French physicist who was analyzing uranium samples from Oklo, Gabon, this prehistoric reactor offers a glimpse of the planet’s extraordinary geological and chemical processes.
The initial clue came from the peculiar composition of uranium isotopes in Oklo ore. Typically, uranium deposits contain 0.72% of the isotope uranium-235which is essential to sustain nuclear reactions. However, the Oklo samples revealed a slightly lower concentration – 0.717%. This small but significant anomaly worsened when it was discovered that some deposits contained as little as 0.4% uranium-235.
Further investigation revealed that these variations were not random, but the result of natural nuclear fission reactions that had occurred around 2 billion years ago. At that time, uranium-235 was much more abundant, allowing for sustained chain reactions under specific conditions.
According to the International Atomic Energy Agency (IAEA), natural uranium deposits today consistently maintain the same isotopic ratiowhether they come from the Earth, the Moon or meteorites.
The Oklo anomaly has raised theories of isotopic fractionation or fission chain reactions. Analyzes soon confirmed this last hypothesis, evidenced by unusual isotopic distributions of rare earth elements and krypton-xenon gas patterns typical of the fission of uranium-235, explains .
This old nuclear reactor worked similar to modern reactorsbut without human intervention. It relied on groundwater to moderate neutron activity, allowing for controlled reactions. As the water heated up and turned into steam, the reaction paused until the water cooled and returned to the tanks, restarting the process. This cycle repeated itself for thousands of years until the fissile uranium material was exhausted.
The conditions necessary for this phenomenon were very specific and are no longer naturally achievable. At the time, uranium-235 was much more abundant and the deposits were located in a water-rich environment that facilitated neutron moderation.
