Oklo nuclear reactor

Curtis, D., Benjamin, T. et al. 1989. The Oklo nuclear reactors cumulative fission yields and nuclear characteristic of reactor 9. Earth and Planetary Science Letters, 89, 193-206. 

Brookins D. G. (1990) Radionuclide behaviour at the Oklo nuclear reactor, Gabon. Waste Manage. 10, 285 -296. 

Curtis, D. B. 1985. The chemical coherence of natural. spent fuel at the Oklo nuclear reactors. Swedish Nuclear Fuel and Waste Management Co. (SKB) Technical Report series, TR 85-04, Stocl olm, Sweden. 

Phenomene d Oklo, Proceedings of a Symposium on the Oklo Phenomenon, International Atomic Energy Agency, Vienna, Proceedings Series, 1975. Natural Fission Reactions, IAEA, Vienna, Panel Proceedings Series STI/PUB/475, 1978, 754 pp. R. West, Natural nuclear reactors. J. Chem. Ed. 53, 336-40 (1976). 

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... 

What convinces scientists that sustained fission once occurred at Oklo is the presence of characteristic fission products in the ore. Elements of mass numbers between 75 and 160 occur in the ore in larger amounts than elsewhere. Furthermore, mass analysis of the elements in Oklo ore shows that they are distributed in the characteristic pattern shown in Figure 22-12. This isotopic signature, which is not found in any other naturally occurring materials, is so characteristic that it has convinced most scientists that the ore deposits at Oklo once formed a huge nuclear reactor. 

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... 

Oklo and Bangombe shows that the geological location, the mineralogy of the hosted rocks, and the chemistry of the fluids are important parameters for the preservation of the uranium deposits and of the natural nuclear reactors and that this information could be used to design and select materials for high-level waste disposal. 

Bros, R., Carpena, J., Sere, V. Beltritti, A. 1996. Occurence of Pu and fissiogenic rare earth elements in hydrothermal apatites from the fossil natural nuclear reactor 16 of Oklo (Gabon). Radio-chimica Acta, 74, 277-282. 

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... 

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. 

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. 

In any case, the primordial radioactivity on the earth was appreciably higher than at present. The ratios of the aetivities at the time of the birth of the earth to those at present are listed in Table 15.4 for some long-lived radionuclides that represent the main radioactive inventory on the earth. The relatively high activity of about 2 10 y ago is the reason for the operation of the natural nuclear reactors at Oklo at that time (seetion 11.8). 

The following section provides detailed information concerning the transport of radionuclides associated with two very different field analogues the Chernobyl reactor accident and the Oklo Natural Reactor. These examples span wide temporal and spatial scales and include the rapid geochemical and physical processes important to nuclear reactor accidents or industrial discharges as well as the slower processes important to the geologic disposal of nuclear waste. 

Menet C., Menager M. T., and Petit J. C. (1992) Migration of radioelements around the new nuclear reactors at Oklo analogies with a high-level waste repository. Radiochim. Acta 58-59(2), 395-400. 

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. 

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