Oklo is a region near
Franceville in the
Haut-Ogooué Province of
Gabon
Gabon ( ; ), officially the Gabonese Republic (), is a country on the Atlantic coast of Central Africa, on the equator, bordered by Equatorial Guinea to the northwest, Cameroon to the north, the Republic of the Congo to the east and south, and ...
. Several
natural nuclear fission reactors were discovered in the
uranium mines in the region in 1972.
History
Gabon was a French colony when prospectors from the
Commissariat à l'énergie atomique (the industrial parts, which later became
Orano Cycle
Orano Cycle, formerly COGEMA (''Compagnie générale des matières nucléaires'') and Areva NC, is a French nuclear fuel company. It is the main subsidiary of Orano S.A. It is an industrial group active in all stages of the uranium fuel cycle, ...
) discovered
uranium
Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...
in the remote region in 1956. France immediately opened mines operated by Comuf () near
Mounana village to exploit the vast mineral resources, and the state of Gabon was given a minority share in the company.
For 40 years, France mined uranium in Gabon. Once extracted, the uranium was used for electricity production in France and much of Europe. Today the uranium deposits are exhausted, and the mine is no longer active. Currently,
mine reclamation
Mine reclamation is the process of modifying land that has been mined to restore it to an ecologically functional or economically usable state. Although the process of mine reclamation occurs once mining is complete, the planning of mine recl ...
work is ongoing in the region affected by the mine operations.
Natural nuclear fission reactor
Some of the mined uranium was found to have a lower concentration of
uranium-235
Uranium-235 ( or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nat ...
than expected, as if it had already been in a
nuclear reactor
A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...
. 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
The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...
times, during the
Statherian
The Statherian Period (; , meaning "stable, firm") is the final geologic period in the Paleoproterozoic Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
Th ...
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
Natural uranium (NU or Unat) is uranium with the same isotopic ratio as found in nature. It contains 0.711% uranium-235, 99.284% uranium-238, and a trace of uranium-234 by weight (0.0055%). Approximately 2.2% of its radioactivity comes from ura ...
had a concentration of about 3%
235U and could have reached
criticality with natural water as
neutron moderator
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, ideally without capturing any, leaving them as thermal neutrons with only minimal (thermal) kinetic energy. These thermal neutrons are immensely ...
allowed by the special geometry of the deposit.
See also
*
List of uranium projects
References
External links
*
*
Alt URL
{{coord, 1, 23, 40, S, 13, 9, 39, E, type:mountain_region:GA_source:nlwiki, display=title
Uranium mines
Radioactive waste repositories
Mines in Gabon
Energy in Gabon
Nuclear reactors