The remnants of nuclear reactors
nearly two billion years old were found in the 1970s in Africa. A scientist
making a routine test noted a tiny "discrepancy" in the amount of
uranium-235 present in some uranium which was undergoing enrichment. Seeking
to explain the discrepancy, scientists began some detective work. These
reactors are thought to have occurred naturally. The fission reaction continued
- off and on - for hundreds of thousands of years. Eventually, the reactor shut
down. No natural reactors exist today, as the relative density of fissile
uranium has now decayed below that needed for a sustainable reaction. Pictured above is Fossil Reactor 15, located in Oklo, Gabon. While it was active, the
natural reactor generated fission products (wastes) very similar to those
produced when fission occurs in modern nuclear reactors at power plants.
Uranium oxide remains are visible as the yellowish rock. Oklo by-products are
being used today to probe the stability of the fundamental constants over
cosmological time and distance scales and to develop more effective means for
disposing of human-manufactured nuclear waste.
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