As if solving a puzzle Whatever it was, it all began in May 1972, when physicist Fracis Perrin from a French nuclear processing plant in Pierrelatte was carrying out an analysis of uranium samples. That’s when he registered an inconsistency in your data. Before him was a piece of natural radioactive uranium ore extracted from the African deposits of Oklo in Gabonwhich indicated that it had a proportion of uranium 235 that represented the 0.717 percent of the total. This was an amount lower than traditionaland that difference was considered an enigma. Not only that, scientists also discovered that other deposits in the area contained only 0.4 percent.
The strangeness arises from the fact that in mineral deposits the isotope 235 normally represents the 0.72 percent from uranium deposits, and its interest lies in the fact that it can be used to create a sustained nuclear reaction, as explained by the International Atomic Energy Agency (IAEA). “If we extracted it from the Earth’s crust, from rocks on the Moon or from meteorites, we would find that.”
However, that piece of Oklo rock was different. The first hypothesis was that it was not natural uranium, but that had undergone artificial fission which had generated the division of some U 235 isotopes and that had caused the alteration of the percentages.
Before continuing, it is worth clarifying, as the Nuclear Forum does, that a nuclear fission It is a reaction in which a heavy nucleus, when bombarded with neutrons, becomes unstable and decomposes into two nuclei. Producing a great release of energy and the emission of two or three neutrons, which in turn cause more fissions, and so on. In a small fraction of a second, the number of nuclei that have fission releases a million times more energy.
However, the initial hypothesis was ruled out after a more detailed study of the sample and researchers in Gabon discovered that the mineral was completely natural and had undergone fission on its own. That meant that in More than two billion years ago, natural fission occurred at this Oklo site.
That is, as the IAEA explains, it necessarily had to contain a critical mass of U 235 to start the reaction. “Back then, that’s how it was.” They calculated that during the Proterozoic Eon of the early Earth, the concentration of uranium-235 isotopes was about 3 percent. An amount that allowed a nuclear fission reaction to be initiated and sustained under the appropriate conditions. And that natural reactor stopped working when uranium levels decreased.
The other ‘ingredient’ necessary for all this to take place was the presence of groundwater. «For a nuclear chain reaction to occur and be maintained, the existence of a moderator is necessary. In this case, water. Without water to slow down the neutrons, controlled fission would not have been possible. In the same way that if there is nothing in an artificial light water nuclear reactor to slow down the neutrons, the fission reactions simply stop,” explains Peter Woods, head of the group in charge of uranium production at the IAEA. «The water acted as moderator in Oklo, absorbing the neutrons and controlling the chain reaction».
And to this are also added the exceptional geological conditions of Oklo. “What makes it so fascinating is that temporal, geological and hydric circumstances have combined so that this could happen,” explains Woods at the IAEA. We are faced with a unique sum of factors that still preserved today and shows traces of its operation.
#natural #nuclear #reactor #Earth #billion #years
