Natural nuclear fission reactor

Part of a series on
The Francevillian basin
Geology and localities
Fossils
(Also see Akouemma)
Evolutionary concepts

A natural nuclear fission reactor is a uranium deposit where self-sustaining nuclear chain reactions occur. The idea of a nuclear reactor existing in situ within an ore body moderated by groundwater was briefly explored by Paul Kuroda in 1956.[1] The existence of an extinct or fossil nuclear fission reactor, where self-sustaining nuclear reactions have occurred in the past, are established by analysis of isotope ratios of uranium and of the fission products (and the stable daughter nuclides of those fission products). The first such fossil reactor was first discovered in 1972 in Oklo, Gabon by researchers from the French Alternative Energies and Atomic Energy Commission (CEA) when chemists performing quality control for the French nuclear industry noticed sharp depletions of fissionable 235
U
 in gaseous uranium made from Gabonese ore.

Oklo is the only location where this phenomenon is known to have occurred, and consists of 16 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 ago, during the Statherian period of the Paleoproterozoic, and continued off and on for a few hundred thousand years, probably never exceeding 100 kW of thermal power during that time.[2][3][4] Life on Earth at this time consisted largely of sea-bound algae and the first eukaryotes living under a 2% oxygen atmosphere. However even this meager oxygen was likely essential to the concentration of uranium into fissionable ore bodies, as uranium dissolves in water only in the presence of oxygen. Before the planetary-scale production of oxygen by the early photosynthesizers groundwater-moderated natural nuclear reactors are not thought to have been possible.[4]

  1. ^ Kuroda, P. K. (1956). "On the Nuclear Physical Stability of the Uranium Minerals" (PDF). Journal of Chemical Physics. 25 (4): 781–782, 1295–1296. Bibcode:1956JChPh..25..781K. doi:10.1063/1.1743058.
  2. ^ Meshik, A. P. (November 2005). "The Workings of an Ancient Nuclear Reactor". Scientific American. 293 (5): 82–86, 88, 90–91. Bibcode:2005SciAm.293e..82M. doi:10.1038/scientificamerican1105-82. PMID 16318030.
  3. ^ Mervin, Evelyn (July 13, 2011). "Nature's Nuclear Reactors: The 2-Billion-Year-Old Natural Fission Reactors in Gabon, Western Africa". blogs.scientificamerican.com. Retrieved July 7, 2017.
  4. ^ a b Gauthier-Lafaye, F.; Holliger, P.; Blanc, P.-L. (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. 60 (23): 4831–4852. Bibcode:1996GeCoA..60.4831G. doi:10.1016/S0016-7037(96)00245-1.