The presence of instinctive nuclear reactors 2 billion years ago beneath Africasounds like a hoax , but it actually happened – they are the only live raw atomic reactor to have existed . By studying the behavior of the ingredient produced , scientists are learning lessons for the storehouse of barren from modern reactors .
The clay of the Gabon reactor in Oklo werefirst discoveredin 1972 , and since then 17 reactor sites have been found nearby . scientist see the site as a potential U mine make the metallic element ’s isotope ratio was different from anywhere else on Earth , indicating induced fission of uranium-235 . The deposit also contained the products of stimulate radioactive decomposition such as neodymium-143 and ruthenium-99 .
A field of study inProceedings of the National Academy of Sciencesdescribes an examination of these products . Although the radioactive decomposition chain initiated during fission is well studied , we know less about how the leave isotope behave if released into the environment . With so many site , and unlike conditions at each , the Oklo reactors providedDr Evan Groopmanof the US Naval Research Laboratory and co - authors with a copious natural laboratory .
Groopman found most cesium ( more than 10 percent of the reactor ' yield ) migrate into the surround environment . Along with barium , much of the cesium was captured by ruthenium some five years after the reactor cease operating , and the metals have remained together ever since . With cesium being themost importantsource of radiation after the nuclear disaster at Chernobyl and Fukushima , this observation could be used to prevent Cs pollution in the time to come .
born atomic reactors could not come today . Chain response normally take at least 3 pct of the uranium fuel to be U-235 . Oklo aside , U deposit are 0.7 percent U-235 and 99.3 pct U-238 . atomic power plant enrich U-235 with centrifuge , a physical process with no innate opposite number .
However , when the Earth first formed , it had almost as much U-235 as U-238 . With a half - life of 700 million year , most of the U-235 has undergo radioactive decline , but half the original U-238 ( half - liveliness 4.5 billion age ) survives .
Even when U-235 was more abundant , however , nuclear reactor required rich uranium repository with water hang through them to slow neutron to make them more easily captured by U-235 nuclei . Even under these circumstances , uninterrupted operation was impossible – Oklo ’s nuclear reactor run for periods of about 30 minutes , before boiling off the water and shutting down for 2 - 3 hours .
So much U-235 underwent nuclear fission at Oklo that today the proportion is notably miserable than in other uranium deposits . The extent of U-235 depletion depends on how long the reactor operated , with periods varying from 24,000 - 1 million years . The paper reports on the situation dub Oklo reactor zone 13 , where almost half the U-235 has been burned up , the highest proportion yet identified , indicating particularly acute reaction .
