Oklo mine

Drozd, R. X, Hohenberg, C. M., Morgan, C. X (1974) Heavy rare gases from Rabbit Lake (Canada) and the Oklo Mine (Gabon) Natural spontaneous chain reactions in old uranium deposits. Earth Planet. Sci. Lett., 23, 28-33. 

Table 1. Migration of fission products and actinides in the "Zone 2" reactor at the Oklo mine.

It all started with a routine analysis in May 1972 at the nuclear fuel processing plant in Pierrelatte, France. A staff member was checking the isotope ratio of U-235 to U-238 in a uranium ore and obtained a puzzling result. It had long been known that the relative natural occurrence of U-235 and U-238 is 0.7202 percent and 99.2798 percent, respectively. In this case, however, the amount of U-235 present was only 0.7171 percent. This may seem like a very small deviation, but the measurements were so precise that this difference was considered highly significant. The ore had come from the Oklo mine in the Gabon Republic, a small country on the west coast of Africa. Subsequent analyses of other samples showed that some contained even less U-235, in some cases as little as 0.44 percent. 

There is convincing evidence that some uranium ores have in past geological epochs sustained natural chain reactions. Some samples of pitchblende, UjOg, from the Oklo Mine in Gabon, Africa, have a U content distinctly lower than... 

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. 

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... 

Abstract The chapter is devoted to the practical application of the fission process, mainly in nuclear reactors. After a historical discussion covering the natural reactors at Oklo and the first attempts to build artificial reactors, the fimdamental principles of chain reactions are discussed. In this context chain reactions with fast and thermal neutrons are covered as well as the process of neutron moderation. Criticality concepts (fission factor 77, criticality factor k) are discussed as well as reactor kinetics and the role of delayed neutrons. Examples of specific nuclear reactor types are presented briefly research reactors (TRIGA and ILL High Flux Reactor), and some reactor types used to drive nuclear power stations (pressurized water reactor [PWR], boiling water reactor [BWR], Reaktor Bolshoi Moshchnosti Kanalny [RBMK], fast breeder reactor [FBR]). The new concept of the accelerator-driven systems (ADS) is presented. The principle of fission weapons is outlined. Finally, the nuclear fuel cycle is briefly covered from mining, chemical isolation of the fuel and preparation of the fuel elements to reprocessing the spent fuel and conditioning for deposit in a final repository. 

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