There is a location in Africa, where self-sustaining nuclear chain reactions have occurred. To be precise, that is the Oklo natural nuclear reactor in Gabon, two billion years old.
Scientists became aware of this reactor accidentally. In 1972, a worker at a nuclear fuel processing plant noticed a confusing detail about one of three isotopes that analyzed material contained. He noticed a discrepancy in the amount of the Uranium 235 isotope. This particular isotope is needed for a nuclear chain reaction. Scientists at the French Atomic Energy Commission (CEA) were amazed by this discovery.
The usual concentration of this isotope in the earth’s crust, on the moon and even in meteorites is 0.720%, while Oklo samples had only 0.717%. This difference was the reason why the scientist conducted additional testing. Test results showed that a certain amount of Uranium 235 was missing from the mine. They concluded that about 200 kg of Uranium 235 was distracted long time ago. With that amount of Uranium 235, it would be possible to make many nuclear bombs. This discovery intrigued scientist from around the world who then expressed their interest and desire to participate in further research.
It turned out that there was an advanced nuclear reactor under the ground and scientist cannot fully understand and explain this discovery. Estimated age of this reactor is about 1.8 billion years and it is believed that it had been functioning for over 500,000 years. Details about this unusual mine were presented at a conference of the International Atomic Energy Agency.
Maybe it sounds impossible, but studies have confirmed that this reactor was much more advanced, comparing to modern nuclear reactors. Scientists now know that the reactor was several kilometers in length and they are amazed by the fact that its thermal impact did not exceed 40 meters in all directions. Additionally, geological characteristics of the area were used to store radioactive waste, which is still in its place in the area of reactor.
The by-product of a nuclear reaction was plutonium and it was possible to control the released energy, and avoid disastrous explosions, because the reaction had been moderated.
Even though the scientist already labeled this reactor as “natural”, not everything about this nuclear reactor is clear. For example, somehow, minerals have been enriched in the past with the purpose of producing a chain reaction. Also, it was discovered that water had been used to moderate the reaction in order to prevent an explosion.
As Dr. Glenn T. Seaborg, former head of the United States Atomic Energy Commission and Nobel Prize winner for his work in the synthesis of heavy elements explained, the water that can be used to moderate the nuclear reaction must be extremely pure. Such water does not exist naturally anywhere in the world, which leaves some questions about the moderated reaction in the natural reactor unanswered.
Some experts came to the conclusion that Uranium in Oklo mine had never been rich enough for a nuclear reaction to happen. Despite that, a reaction happened somehow, leading the scientists to believe that the original Uranium was far richer in Uranium 235 than that in a natural formation.