While Americans pride themselves on being able to unlock the secrets of the atom for military purposes as well as sustainable energy, it seems that the mother nature is still able to solve even the most complex problems well before us. In 1972, French physicist Francis Perrin made an interesting discovery in Oklo, Africa. While mining uranium ore, he discovered that the concentration of uranium 235 was less than what is typically found in uranium ore samples. Uranium 235 can be found to make up 0.720 percent of an uranium sample but samples taken in Oklo showed a decrease to 0.717 percent. This may not seem like much but, with the large amount of ore in the mine, the small decrease showed that nearly 200 kilograms had been missing.
[Source: The Ages of Gaia]
With further research the mine showed that it had the proper conditions for a natural nuclear reaction to take place. Since uranium 235 only reacts to slow moving neutrons before it decays into more stable elements, water must be present to absorb the kinetic energy of the neutrons. Uranium 235 releases energy in the form of heat when interacting with its surroundings and caused the water in the cave to heat up enough to evaporate. The nuclear reaction would then stop with the neutrons moving too fast to interact with the Uranium and the water continued to flow back to where it had been before it evaporated. This continued until the amount of uranium-235 was too small to sustain a reaction.
With 16 sites in the Oklo mine, the estimated power output was 100 kilowatts. This is enough to power close to 1000 modern television sets but with this energy not being put to good use, all it did was contribute to global warming. While this was not a just cause, the fact that nature figured out how to set up the proper conditions for uranium to decay in a controlled cycle before us is fascinating. This leaves a sense of wonder and also a sense of fear with the possibility of other naturally occurring nuclear reactors still to be found.