Oklo, the Natural Nuclear Reactor

LE POINT - 18 November 2004 - by Frédéric Lewino

Not only did nuclear fission exist two billion years ago, long before man appeared on the planet. In addition to this, in Gabon, nature has discovered how to store nuclear waste and isolate it from the environment.

«Oklo was working like a geyser. » The American professor of physics, Alexander Meshik, of the University of Washington, at Saint-Louis (Missouri), says he has understood the secret of the natural nuclear reactor discovered in 1972 at Oklo in Gabon.

Two billion years ago, in a sedimentary layer of earth rich in uranium, a nuclear fission chain reaction occurred and kept running during 150 million years.

By measuring the proportion of nine isotopes of xenon in a minuscule sample of rock taken from Oklo, this scientist has demonstrated the existence of a periodic cycle of three hours in the chain reaction. First : the chain reaction starts in the sedimentary layers rich in fissile uranium 235 and immersed in water. The temperature then rises, vaporizing the water around the uranium. Second : the water vapor produced then do not slow down the neutrons any more, which stops the chain reaction. The temperature then falls, the water vapor recondenses and neutrons are again slowed down, which initiates the chain reaction again. After two hours and a half, the chain reaction starts again. And so on...

But Meshik is also fascinated by a sample of aluminophosphate (mixture of lanthane, eérium, strontium and calcium) which has trapped xenon and krypton 85, produced by the chain reaction. « It is fascinating to think that a natural nuclear reaction can reach the critical conditions, and that it is also capable of storing its own waste. »

One then thinks about today's nuclear industry not knowing how to handle its nuclear waste. Perhaps Oklo could teach us lessons and bring useful indications regarding the safe storage of nuclear waste during two billion years.


Other documents on the natural nuclear reactor at Oklo : http://www.ecolo.org/documents/listdoc-en.htm
then scroll down to the "natural radioactivity" section

EFN's home page : www.ecolo.org (Environmentalists For Nuclear Energy)