A prehistoric natural “nuclear reactor”, which was in operation about 2 bn years ago, was discovered in the Natural radioactive element with the atomic number 92. The n... deposit Oklo/Gabon in 1972. In past years, six further locations in this deposit were found where a self-perpetuating Self-perpetuating reaction. In a fission chain reaction, a f... must have taken place due to the reduced U-235 content in the Uranium in the isotope composition occurring in nature, Natu.... For the Oklo II location, it can be calculated from the Reduction of the relative frequency of a nuclide or several ... of uranium-235 entailed by See 'nuclear fission'. that a minimum of 4 t U-235 must have been fissioned, 1 t Pu-239 formed, and a volume of heat of about 100 bn kWh generated. As a comparison: in the System used to initiate, maintain and control a fission chai... of a Thermal power plant, primarily used for electricity generati... of the 1,300 Megawatt electric; electric output of a power plant in megaw... category, about 30 bn kWh heat is generated by See 'nuclear fission'. annually.