What is the Oklo natural nuclear fission reactor?

The Oklo natural nuclear fission reactor refers to a set of sixteen sites in the uranium mines of Gabon where self-sustaining nuclear chain reactions occurred naturally about 1.7 billion years ago. Discovered in 1972 by French researchers, these sites remain the only known locations on Earth where natural nuclear fission is known to have taken place. The reactions were moderated by groundwater and made possible by the presence of oxygen in Earth's ancient atmosphere, which allowed uranium to dissolve and concentrate into fissionable ore bodies.

What we know

• Several natural nuclear fission reactors were discovered in 1972 in the uranium mines of Oklo, a geological region near Franceville in Gabon. [2, 3]
• The existence of the Oklo reactors was confirmed through analysis of isotope ratios of uranium and fission products. [3]
• Self-sustaining nuclear fission reactions at Oklo took place approximately 1.7 billion years ago during the Statherian period and continued off and on for a few hundred thousand years. [3]
• Planetary oxygen was likely essential for concentrating the uranium into fissionable ore bodies, as uranium dissolves in water only in the presence of oxygen. [3]

Where to go next

• whoWho proposed the existence of natural nuclear reactors?
• whereWhere is the Oklo geological region located?
• how it workedHow do groundwater and uranium deposits interact in nature?
• the bigger pictureWhat are small modular reactors?
• whenWhen did multi-site nuclear fission operate at Oklo?
• an unexpected connectionHow does ancient nuclear fission relate to modern artificial power plants?Natural fission at Oklo occurred billions of years before humans constructed the first artificial nuclear power plants in the 1950s.

Sources

• [1]Oklo (Wikidata Q26761) · CC0 1.0
• [2]Oklo · CC BY-SA 4.0
• [3]Natural nuclear fission reactor · CC BY-SA 4.0
• [4]Small modular reactor · CC BY-SA 4.0
• [5]Nuclear power · CC BY-SA 4.0