Monday, November 28, 2005

African Nuclear Reactors

Thanks to all of you who sent me links to the real African nuclear reactors. Although, sadly, I think my neighbors claim that they must have been made by the space aliens lacks, um, credibility. However, it's still pretty amazing. Here's a nice picture and a short description (thanks William Boon):

Here's the Wikipedia explanation (sent in by DQ reader Donna Kidwell):
A natural nuclear fission reactor can occur under certain circumstances that mimic the conditions in a constructed reactor. The only known natural nuclear reactor formed 2 billion years ago in Oklo, Gabon, Africa. Such reactors can no longer form on Earth: radioactive decay over this immense time span has reduced the proportion of U-235 in naturally occurring uranium to below the amount required to sustain a chain reaction.

The natural nuclear reactors formed when a uranium-rich mineral deposit became 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.

These natural reactors are extensively studied by scientists interested in geologic radioactive waste disposal. They offer a case study of how radioactive isotopes migrate through the earth's crust. This is a significant area of controversy as opponents of geologic waste disposal fear that isotopes from stored waste could end up in water supplies or be carried into the environment.

Here's the Wikipedia link about Oklo, which is also interesting:

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