Oklo, the Two Billion Year Old Nuclear Reactor

Scientists discovered that the Oklo mine in Gabon, Central Africa, had less Uranium-235 than expected, leading to the realization that it was the site of a natural nuclear reactor from 2 billion years ago. This reactor operated under specific conditions, with Uranium-235 and neutrons present, and groundwater acting as a moderator to control the reaction. The cycle of reaction and cooling continued for hundreds of thousands of years until the uranium was depleted, leaving behind evidence of this ancient natural phenomenon.

What was the initial clue that led scientists to investigate the Oklo mine?

• The presence of unusual minerals

• A lower than expected concentration of Uranium-235

• Strange geological formations

• High levels of radiation

Which isotope of uranium is crucial for nuclear reactions due to its ability to release significant energy?

• Uranium-235

• Uranium-234

• Uranium-236

• Uranium-238

What role did groundwater play in the natural nuclear reactor at Oklo?

• It slowed down neutrons to sustain the reaction

• It absorbed excess radiation

• It accelerated the reaction

• It provided additional uranium

How did the natural nuclear reactor at Oklo prevent a runaway reaction?

• By boiling off groundwater to stop the reaction

• Through the natural decay of uranium

• By using control rods

• By releasing excess neutrons into the atmosphere

What eventually caused the natural nuclear reactor at Oklo to stop operating?

• The introduction of foreign elements

• A geological shift

• The depletion of Uranium-235

• A sudden increase in temperature