Natural nuclear fission reactor

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A natural nuclear fission reactor is a uranium deposit where self-sustaining nuclear chain reactions occur through natural geological processes rather than human construction. The possibility of such reactors existing in situ within an ore body moderated by groundwater was proposed by Paul Kuroda in 1956. The first confirmed example was discovered in 1972 in Oklo, Gabon, by researchers from the French Atomic Energy Commission (CEA) after chemists detected sharp depletions of fissile 235U in gaseous uranium hexafluoride made from Gabonese ore. The existence of the Oklo reactors was confirmed through analysis of isotope ratios of uranium and of the fission products (and the stable daughter nuclides of those fission products). Oklo remains the only known location where this phenomenon is known to have occurred, consisting of sixteen sites with patches of centimeter-sized ore layers. There, self-sustaining nuclear fission reactions are thought to have taken place approximately 1.7 billion years...

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