![]() ![]() Without water, itwould have been nearly impossible for natural reactors to sustainchain reactions. These scientists believe that water filtering downthrough crevices in the rock played a key role. Scientists fromaround the world, including American scientists have studied therocks at Oklo. So how did nuclear reactions occur innature?ĭeep under African soil, about 1.7 billion years ago, naturalconditions prompted underground nuclear reactions. This is high enough to permit nuclearfissions to occur, providing other conditions areright. 5 Any change in thisratio indicates some process other than simple radioactive decay.Ĭalculating back to 1.7 billion years ago the age of the deposits inGabon scientists realized that the U-235 there comprised about threepercent of the total uranium. At present, U-238comprises about 99.3 percent of the total, and U-235 comprises about0.7 percent. Generally, uranium isotope ratios are the same in all uranium orescontained in nature, whether found in meteorites or in moon rocks.Therefore, scientists believe that the original proportions of theseisotopes were the same throughout the solar system. Thus, over time the proportion of U-235 to U-238 decreases.But this change is slow because of the small rates of decay. Inparticular, U-235 decays about six-and-a-third times faster thanU-238. All of these isotopesundergo radioactive decay, but they do so at different rates. The uranium in the Earth contains dominantly two uranium isotopes,U-238 and U-235, but also a very small percentage of U-234, andperhaps small, undetectable amounts of others. Uranium isotopes decay at differentlevels Perrin and the other French scientists concluded that the only otheruranium samples with similar levels of the isotopes found at Oklocould be found in the used nuclear fuel produced by modern reactors.They found that the percentages of many isotopes at Oklo stronglyresembled those in the spent fuel generated by nuclear power plants,and, therefore, reasoned that a similar natural process hadoccurred. "How," they asked, "could fission reactions happen innature, when such a high degree of engineering, physics, and acute,detailed attention went into building a nuclear reactor?" ![]() Some argued that the missing amountsof U-235 had been displaced over time, not split in nuclear fissionreactions. Scientists from other countries were skeptical when first hearing ofthese natural nuclear reactors. ![]() This isotope is rare in nature, but insome places, the uranium found at Oklo contained only half the amountof the isotope that should have beenthere. Some uranium samplesfrom Gabon had an abnormally low amount of the isotope U-235, whichcan sustain a chain reaction. ![]() All atoms of a specific chemical element have the samechemical properties, but may differ in weight these differentweights of an element are known as isotopes. In the early 1970s, French scientists noticed something odd aboutsamples of uranium recovered from the Oklo mine in Gabon, WestAfrica. But if a repository were to be built atYucca Mountain, scientists would count on the geology of the area tocontain radionuclides generated by these wastes with similareffectiveness. No nuclear chain reactions will ever happen in a repository forhigh-level nuclear wastes. 2Īnd when these deep underground natural nuclear chain reactions wereover, nature showed that it could effectively contain the radioactivewastes created by the reactions. These are collectively known as the OkloFossil Reactors. 1 Fifteen natural fissionreactors have been found in three different ore deposits at the Oklomine in Gabon, West Africa. Indeed, heargued, nature had a two-billion-year headstart. It came as a great surprise to most, therefore, when, in 1972, Frenchphysicist Francis Perrin declared that nature had beaten humans tothe punch by creating the world's first nuclear reactors. In a power plant,sustaining the process of splitting atoms requires the involvement ofmany scientists and technicians. Thissplitting process is called nuclear fission. In power plants, itinvolves splitting uranium atoms, and that process releases energy asheat and neutrons that go on to cause other atoms to split. OKLO natural nuclear reactor Oklo: Natural Nuclear ReactorsĬreating a nuclear reaction is not simple. ![]()
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