Fission for Explanations: Gabon’s Natural Nuclear Reactors

Nuclear power is a controversial topic among people who care for the environment, but nature was creating nuclear power long before humans have even been inhabiting the planet. Natural nuclear reactors have been found in Oklo, Gabon: these African natural fossil reactors have been radioactively dated to be roughly two billion years old. While they no longer function, they are providing very important information that is helping to increase our understanding of our planet.

First discovered in the 1970s, the natural fossil reactors rest in the grassy highlands of the African country of Gabon. Following the discovery of extensive highly enriched Uranium deposits in the 1960s, a minesite and processing plant were built to extract the valuable material from the ground. But mining was temporarily halted when the ancient nuclear reactors were discovered in order to allow geological research of the sites. Some of the reactors remain intact today, some have been completely mined out, but all ceased to function hundreds of millions of years ago. Since then, the radioactive material has been degrading naturally and today harmless. As far as anyone knows, this handful of sites in Gabon represent the only naturally occurring nuclear reactors on the planet.

(all images via: Curtin University)

The natural reactors occurred because two billion years ago, the Earth contained a high concentration of Uranium-235. U-235 is a naturally occurring fissile uranium isotope that is found throughout the entire Solar System. The density and abundance of U-235 along with the scarcity of neutron absorbers, a high concentration of a moderator (like water) and a size appropriate to sustain the fission reactions all contributed to the formation of these incredible natural reactors. Today, these conditions are not met anywhere on Earth and so no natural nuclear reactors are operational. All of this information would be interesting, but not very useful if not for the fact that we aren’t quite sure what to do with our own man-made radioactive waste. Observing the degraded remains of these naturally-occurring fossil reactors is helping scientists gain a firmer handle on the issue of radioactive waste containment.

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