Geek Trivia: (Melt)down to Earth

Where is the world's only known naturally occurring nuclear reactor located — a geological formation that induced and maintained a fission chain reaction without any human intervention?

Where is the world's only known naturally occurring nuclear reactor located — a geological formation that induced and maintained a fission chain reaction without any human intervention?

In the Oklo region of the Central African republic of Gabon, you'll find an exhausted uranium mine that, were you to go back in time about 1.5 billion years to the Precambrian, would have been chugging away as the world's only nature-made nuclear fission reactor. (Reason No. 9,153 that having a time machine would rock.)

Now, don't go picturing a big lightning-bolts-and-mushroom-clouds event where Mother Nature conjures up an Industrial Light and Magic-worthy meltdown of apocalyptic proportions. The Oklo reactor is really just a geological formation that had the fantastical luck of arranging itself in the perfect fashion to coax some sustained fission chain reactions out of its uranium deposits, none of which likely did much more than throw off some heat, electricity, and radiation that was probably utterly unnoticed by the primitive Mesoproterozoic microbes that were only just then developing the physical capabilities to accommodate sexual reproduction, let alone Geiger counters or Greenpeace demonstrations.

The formation in its most basic form was a vein of uranium ore sandwiched between two layers of sandstone. Groundwater filtered through the sandstone and acted as a neutron moderator, allowing for sustained fission reactions. As the reactions threw off heat, the groundwater evaporated, suspending the reactions and preventing meltdown. This process continued off and on for several hundred thousand years, depleting the U235 content of the ore, which is usually about 0.72 percent.

In 1972, when French nuclear energy officials noted that certain shipments of ore from the Oklo mine did not contain the predictable 0.72 percent of U235, they launched an investigation, fearing that someone had made off with fissile material. After extensive review, they arrived at the unlikely conclusion that uranium ore had been fissioned through natural geological processes — a possibility that had been predicted by University of Arkansas researcher Paul Kuroda in 1956 — but had never been observed before or since.

Despite a few hundred millennia of self-depletion, the Oklo mine still had enough fuel to support 40 years of extraction, 16 of which went by before anyone noticed they were dealing with a natural nuclear reactor. That's not just an explosive geophysical surprise — it's some radioactively radical Geek Trivia.

The Quibble of the Week

If you uncover a questionable fact or debatable aspect of this week's Geek Trivia, just post it in the discussion area. Every week, yours truly will choose the best post from the assembled masses and discuss it in a future edition of Geek Trivia.

This week's quibble comes from the October 24 edition of Geek Trivia, "Flying by the (ejection) seat of your pants." TechRepublic member Gezelig dinged me for not having the most up-to-date info on the remaining flights of the space shuttle program.

"Not so much a quibble as perhaps an update. You say, 'STS-125 will be Atlantis' last spaceflight,' yet here you find this: 'The shuttle program is finalizing the approval of a manifest acceleration that will shake up the remaining flights of the shuttle to ease the Constellation schedule. NASA Associate Administrator for Space Operations Bill Gerstenmaier has been holding meetings on Wednesday to approve the changes, which include flying Atlantis for an additional two flights, adding STS-131 and STS-133 logistics flights to the confirmed schedule, and ending the shuttle program earlier — at the end of March 2010.'"

Never underestimate the power of a government enterprise to extend its operating life. Thanks for the update, and keep those quibbles coming.

Falling behind on your weekly Geek fix?

Check out the Geek Trivia Archive, and catch up on the most recent editions of Geek Trivia.

Test your command of useless knowledge by subscribing to TechRepublic's Geek Trivia newsletter. Automatically sign up today!

By Jay Garmon

Jay Garmon has a vast and terrifying knowledge of all things obscure, obtuse, and irrelevant. One day, he hopes to write science fiction, but for now he'll settle for something stranger — amusing and abusing IT pros. Read his full profile. You can a...