Uranium Gabon reactor

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). 

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... 

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... 

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. 

Salah, S. 2000. Weathering Processes at the Natural Nuclear Reactor of Bangombe Gabon). Identification and Geochemical Modeling of the Retention and Migration Mechanisms of Uranium and Rare Earth Elements. PhD thesis, Universite Louis Pasteur, Strasbourg, France. 

Del Nero, M., Salah, S., Miura, T., Clement, A. Gauthier-Lafayf., F. 1999a. Sorption/deso-rption processes of uranium in clayey samples of the Bangombe natural reactor zone, Gabon. Radiochimica Acta, 87, 135-149. 

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. 

Beyond radioactivity, nuclear energy occurred spontaneously on Earth when sustained fission reactions developed spontaneously in the uranium mine of Oklo in Gabon in Africa, showing the path towards fission reactors about 2 billion years ahead. 

In 1972, evidence of a past "natural nuclear reactor" was found by a French mining geologist while assaying uranium samples in a uranium mine at Oklo, Gabon, West Africa It "went critical" about 1.7 billion years ago, released 15,000 megawatt-years of energy by consuming six tons of uranium, and was critical (at low power) for several hundred thousand years. 

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,... 

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... 

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. 

---