Google Earth Community: 2 Billion year old nuclear reactors.

Around 2 billion years ago, something happened naturally at the site of the present-day, but now closed, Oklo uranium mine in the west African Republic of Gabon. And it kept happening for for hundreds of thousands of years.
From Science News:
“Scientists explain the formation of what has turned out to be 18 reactors in and near Oklo without invoking exotic physics or visitations by space aliens. The sites were fortuitous accumulations of uranium that went critical for a while. Still, many researchers are awed that nature could achieve this result—something that people accomplished only after centuries of scientific and technological advancements”
“Using sophisticated microanalysis techniques, the St. Louis scientists have extracted major new findings about how the natural reactors might have operated. As a practical bonus, Meshik notes, the results might also point toward better ways to immobilize radioactive waste from nuclear-power plants”.
“Over many millennia of operation, every cycle would have generated the same mix of xenon isotopes. The researchers have used the known rates of all of those xenon-producing processes and the isotope concentrations that they have measured in their sample to calculate that the reactor turned on for about half an hour and then shut down for some two-and-a-half hours before turning on again.
Since the earliest Oklo studies, scientists have proposed a role for water in the creation of the natural reactors. According to the leading theory, deposits of the radioactive metal formed when water running off vegetation-free landmasses carried uranium compounds to the delta of an ancient African river. The theory holds that early biological processes produced oxygen that accumulated in the planet's atmosphere and oxidized the uranium, making it soluble."
"Once those compounds had settled in the delta, geological processes such as uplifting of earth layers and erosion eventually positioned the deposits of concentrated uranium underground, where they were bathed in enough water to start the chain reactions. Under those circumstances, the scientists propose that in each 30-minute active phase, the reactor became so hot that the water boiled away and the reactor stopped working. Then, as the reactor cooled, inflowing water no longer evaporated and so could again slow down neutrons, restarting the cycle”.
The reactors eventually shut down because the fissionable uranium isotope decayed radioactively – its half-life left too little of the fissionable isotope.

For a more detailed explanation see this web page and this web page and this web page

Note: This location originally started out as a fun and games challenge. It turned out to be not much of a challenge, but deserves a spot in Nature and Geography

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Edited by Hill (12/13/06 01:35 PM)

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