Gabon, Oklo natural reactors

Toulhoat, P., Gallien, J. P. et al. 1996. Preliminary studies of groundwater flow and migration of uranium isotopes around the Oklo Natural Reactors (Gabon). Journal of Contaminant Hydrology, 21, 3-17. 

Bangombe, Oklo natural reactors, Gabon Natural Analogue 0.25 — 25-500 Presence of a weathered zone. Groundwater chemistry controlled by the Fe " /Fe(OH)3 equilibria. Fluids are not enriched in CO2. 

The Oklo natural reactors in Gabon are the best natural analogues for assessing the geological behaviour of fission products and actinides (see also Gauthier-Lafaye et al. 2004). Elements that were compatible with the U ore structure were retained, whereas elements that... 

Information on the interaction of radionuclides with ground-water in deeply-buried, high-level, long-term "waste repositories" is available at only a few locations. One is the OKLO natural reactor in Gabon which has for over 1. 7 billion years retained some of the radionuclides also present in nuclear wastes (5). Another is the Nevada test Site, where radionuclides were first deposited underground on September 19, 1967 during the 1.7 kt... 

Cuney M. and Mathieu R. (2000) Extreme fight rare earth element mobilization by diagenetic fluids in the geological environment of the Oklo natural reactor zones, EranceviUe Basin, Gabon. Geology 28, 743—746. 

The Oklo natural reactor in Gabon, Africa, is a high-grade sandstone-hosted U deposit. It was formed about... 

Plutonium does not exist as a naturally occurring element with the exception that small amount of Pu generated in the natural reactors (the Oklo natural reactor in Gabon). The primary input of Pu to environment is fallout from nuclear weapon tests and accident release (e.g., the Windscale accident in 1957 and the Chernobyl accident in 1986). Three of the most common of the 15 known Pu isotopes are Pu (94%), °Pu (6%), and Pu (0.4%). Pu has a half-life of 24,000 yr. Its (X-dccay results in production of (Tj/2 = 700 million yr). Pu has a half-life of 6560 yr, emits a particles and decays to U (T1/2 = 20 million yr). Due to (he long half... 

The Natural Reactor. Some two biUion years ago, uranium had a much higher (ca 3%) fraction of U than that of modem times (0.7%). There is a difference in half-hves of the two principal uranium isotopes, U having a half-life of 7.08 x 10 yr and U 4.43 x 10 yr. A natural reactor existed, long before the dinosaurs were extinct and before humans appeared on the earth, in the African state of Gabon, near Oklo. Conditions were favorable for a neutron chain reaction involving only uranium and water. Evidence that this process continued intermittently over thousands of years is provided by concentration measurements of fission products and plutonium isotopes. Usehil information about retention or migration of radioactive wastes can be gleaned from studies of this natural reactor and its products (12). 

Introducing the values into the equation, using a minimum Kd-value of >300, gives a retention factor of >750. If this value is combined with a representative water transport time from repository to recipient (>1000 years for a distance >100 m), the transport equation indicates that it will take the plutonium >750,000 years to reach the recipient which is the water man may use. This estimate is supported by findings at the ancient natural reactor site at Oklo in Gabon (67). 

It may seem unlikely that all these conditions could have been met, but at least one deposit of uranium ore has characteristics indicating that, long ago, it operated as a natural nuclear reactor. At Oklo in the Gabon Republic near the western coast of equatorial Africa (see photo), there are uranium deposits of high purity... 

Hidaka, H. Holliger, P. 1998. Geochemical and neutronic characteristics of the natural fossil fission reactors at Oklo and Bamgombe, Gabon. Geochimica et Cosmochimica Acta, 62, 89-108. 

Hidaka, H., Holliger, P. Gauthier-Lafaye, F. 1999. Tc/Ru fractionation in the Oklo and Bangombe natural fission reactors (Gabon). Chemical Geology, 155, 323-333. 

Some billion years ago natural nuclear reactors must have operated and generated Tc as a high yield fission product by induced fission of with slow neutrons. The relics of a natural reactor were discovered in 1972 at the Oklo uranium mines in the Republic of Gabon, Africa. lire Oklo phenomenon occurred 1.72 billion years ago and produced a greater amount of Tc than detected in other uranium ores [20. Ruf-fenach et al. [21] reported values of integrated flux of thermal neutrons for the Oklo uranium ores of up to 1. . 2 10 n cm and a atomic ratio down to 0.00410,... 

CFF-Xe. Isotopic Xe anomalies, characterized by enriched Xe, Xe and Xe relative to fission Xe, were identified within minerals from the natural nuclear reactor no.2 in the Oklo uranium mine, Gabon (Shukolyukov et al. 1976). Although early theories focused on a nuclear process to account for this observation, it later became apparent that this was a chemical fractionation effect (Meshik and Shukolyokov 1986 Meshik 1988). CFF-Xe, or Chemically Fractionated Fission-Xenon is created when fast... 

Radioactivity, radioactive elements and nuclear reactors are found in nature. There are at least 14 natural fission reactors in the Oklo-Okelobon-do natural uranium formation in Gabon on the west coast of Africa. These fossil reactors had sufficient amounts of U-235 to allow chain reactions to... 

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