OKLO natural reactor in Gabon

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... 

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... 

We should not leave our discussion of nuclear reactors without mentioning the Oklo phenomenon. In 1972, French scientists analyzing uranium ore from the Oklo uranium mine in Gabon found ore that was depleted in 235U. Further investigation showed the presence of high abundances of certain Nd isotopes, which are formed as fission products. The relative isotopic abundances of these isotopes were very different from natural abundance patterns. The conclusion was that a natural uranium chain reaction had occurred 1.8 billion years ago. 

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. 

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 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). 

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... 

There are indications that this method will isolate the waste until the radioactivity decays to safe levels. One reassuring indication comes from the natural fission reactor at Oklo in Gabon, Africa. Initiated about 2 billion years ago when uranium in ore deposits there formed a critical mass, the reactor produced fission and fusion products for several thousand years. Although some of these products have migrated away from the site in the intervening 2 billion years, most have stayed in place. Another indication of the possible success of... 

The Oklo anomaly, which was discovered as a result of isotopic assays of uranium from the Mounana mill, was first recognized as being the result of a natural fission reactor in 1972 (1,2). The Oklo uranium deposit, located in the southeast part of Gabon, occurs in one of the Francevillian series of sedimentary deposits. In the deposit the uranium concentration is... 

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,... 

Determination of a fission track age requires several further experimental steps to measure the uranium concentration. The uranium concentration is not measured directly, but a second set of fission tracks is created artificially in the sample by a thermal neutron irradiation. This irradiation induces fission in a tiny fraction of the atoms, which are present in a constant ratio to U in natural uranium. Knowing the total neutron fluence received during irradiation, the number of induced tracks provides a measure of the uranium concentration of the grain. Because the induced tracks are derived from a different isotope of uranium than the spontaneous tracks an important consideration in fission track dating is the assumption that the isotopic ratio of the two major isotopes of uranium, and is constant in nature. With the notable exception of the unique natural nuclear reactors of Oklo in Gabon (Bros et al. 1998), where this isotopic ratio is disturbed, this is a very safe assumption. Numerous measurements have shown that and are always present in their natural abundances of 0.73% and 99.27%, respectively. 

French scientists discover ancient natural nuclear reactor in Oklo, Gabon. 

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