"Nuclear fission chain reactions occur in nature.
In 1972, scientists at the French Atomic Energy Establishment at Pierrelatte discovered the nearly intact remains of a natural nuclear fission reactor in a 0.5-m-thick seam of uranium ore located at Oklo, in the Republic of Gabon (7).
Subsequently, other reactor zones were discovered in the region and appear to have functioned as self-sustained nuclear fission reactors about 1,800 million years ago (8).
At the time that the Oklo reactor was active, the proportion of 235U in natural uranium was sufficiently great for nuclear fission chain reactions to occur in a thick mass of natural uranium ore.
In addition to functioning as a thermal neutron reactor moderated by ground water, the Oklo reactor also functioned as a fast-neutron breeder reactor, producing additional fissile material in the form of plutonium and other transuranic elements (9)."
OMG!
Nuclear energy is "natural."