Oklo, Gabon. A total of 17 natural nuclear reactors are igniting. Nuclear waste of the same type and percentage as modern nuclear reactors is evident: the dreaded plutonium-239, which in its decay process generates a whole series of fission byproducts found precisely (within 1 ppm) in the percentages predicted by theory. Considering that the reactors are 1.7 billion years old, it can be concluded that the laws of physics (at least the weak interaction) have changed by less than 1 ppm in the last 2 billion years! The fortunate combination is a mixture of uranium, water, and cyanobacteria. Bacteria make the water acidic, which corrodes the uranium (at the time, uranium-235, the fissile one, accounted for 3% of the U238, while today it’s only 0.7%), then algae and soil filter the uranium, and when the water evaporates, the uranium-235 is found in sufficient concentration to trigger the reaction. When it shuts down due to exhaustion of the fissile fuel, the cycle begins again. Water also acts as a neutron slower (as Enrico Fermi would later realize), making them prey to the nuclei. In 150,000 years of operation, the 17 natural nuclear reactors consumed a whopping 6.5 tons of uranium, with cycles of approximately 150 minutes. A galactic marvel (in every sense).
