The first nuclear reactor? Nature thought of this two billion years ago. When we think of nuclear reactors, we imagine imposing man-made structures, symbols of technological innovation and controversies related to their environmental impact. But what if I told you that nature had already created a fully functional nuclear reactor billions of years before human science understood its principles? This story takes us to the heart of Africa, to Gabon, where a uranium deposit surprised the world scientific community.
An anomaly in the rocks
It was 1972 when a physicist, analyzing uranium samples from the Pirlat nuclear plant in France, noticed something strange. Typically, natural uranium contains three main isotopes: uranium-238, uranium-235 And uranium-234. Of these, uranium-235 is the rarest, accounting for only 0.72% of total reserves, but it is also critical for triggering nuclear reactions. Yet, in the samples analyzed, the percentage of this isotope dropped to 0.717%. A seemingly negligible difference, but enough to raise alarm bells among experts.
The traces of uranium came from the Oklo deposit in Gabon. When scientists began to investigate, they discovered that the anomaly was no coincidence. On the contrary, it was the result of one self-sustaining natural nuclear reaction occurred approximately two billion years ago. This phenomenon, unique in the geological history of our planet, occurred thanks to a combination of exceptional factors.
According to the United States Geological Survey report, the evidence was clear: from the unusual distribution of uranium isotopes to the isotopes of noble gases such as krypton and xenon, unmistakable markers of nuclear fission.
How the natural nuclear reactor worked
Two billion years ago, the abundance of uranium-235 was significantly higher than today, about 3%, enough to allow spontaneous fission. The element that made the stability of the process possible was underground water: it acted as a natural moderator, slowing down the neutrons in a similar way to what happens in modern reactors.
When the water heated up and evaporated, the reaction stopped, only to resume when the temperature dropped and the water began to flow again. This self-regulating cycle continued for hundreds of thousands of years, generating power estimated at around 100 kilowatts. Eventually, the natural reactor shut down, slowly dismantling itself.
The discovery of the Oklo natural reactor is not only an extraordinary chapter in geology, but also offers an important lesson for the present. It shows how nature, with its complex chemical and physical interactions, is capable of performing feats that still fascinate science today.
For researchers, this phenomenon represents a sort of natural laboratory that allows them to study processes that might otherwise be difficult to replicate. For us all, it is a reminder of how our planet hides extraordinary secrets, yet to be discovered.
