|
Oklo is a place in the West African state of Gabon.
It is famous as the locale of a number of sites at which self-sustaining nuclear fission reactions took place approximately 2 billion years ago. This fact was discovered in 1972 when measurements of the relative abundances of the two most significant isotopes of the uranium mined there showed an anomalous result compared to those obtained for uranium from other mines.
The natural nuclear reactor formed when a uranium-rich mineral deposit got
inundated with groundwater that acted as a neutron moderator, and a strong
chain reaction took place. The water moderator would boil away as the reaction increased, slowing it back down again and preventing a meltdown. The fission reaction was sustained for hundreds of thousands of years.
A key to the creation was that at the time, the abundance of fissionable U-235 was about 3%. Due to U-235's shorter half life than U-238, the current abundance of U-235 in natural uranium is about 0.7%. Therefore a natural nuclear reactor is no longer possible on Earth.
External links
|
