Oklo

Natural nuclear fission reactor

Some of the mined uranium was found to have a lower concentration of uranium-235 than expected, as if it had already been in a nuclear reactor. When geologists investigated they also found products typical of a reactor. They concluded that the deposit had been in a reactor: a natural nuclear fission reactor, around 1.8 to 1.7 billion years BP – in the Paleoproterozoic Era during Precambrian times, during the Statherian period – and continued for a few hundred thousand years, probably averaging less than 100 kW of thermal power during that time. At that time the natural uranium had a concentration of about 3% 235U and could have reached criticality with natural water as neutron moderator allowed by the special geometry of the deposit.

References

References

1. Kean, Sam. (12 July 2010). "The Disappearing Spoon: And Other True Tales of Madness, Love, and the History of the World from the Periodic Table of the Elements". Little, Brown.
2. (2004). "Symmetry and the Beautiful Universe". Prometheus Books.
3. Zoellner, Tom. (2009). "Uranium". Viking Penguin.
4. (1976). "A Natural Fission Reactor".
5. Cowan, George. (1976). "Oklo – A Natural Fission Reactor". Los Alamos Scientific Laboratory.
6. (December 1996). "Natural fission reactors in the Franceville basin, Gabon: A review of the conditions and results of a 'critical event' in a geologic system". Geochimica et Cosmochimica Acta.
7. Meshik, Alex P.. (2005-11-01). "The Workings of an Ancient Nuclear Reactor".