This crazy thing must have been outrageous when it was operating. How did nearby wildlife adjust? Boiled fish every few hours: a paradise for scavengers (if they could handle the radiation)! Interesting new research by Meshik, et al.:
In 1972, a site with the necessary conditions for self-sustained fission was found at the Oklo mine in Gabon: A 2-billion-year-old uranium deposit some 5-10 meters thick and 600-900 meters wide was bathed by an ancient river. That natural reactor is estimated to have operated at an average power of 100 kW over its 150,000-year lifetime.
By examining in detail the reactor's krypton and xenon isotopes in grains of aluminous hydroxy phosphate, physicists at Washington University in St. Louis have now discovered the reactor's operating cycle: 30 minutes on followed by 2.5 hours off. While on, the reactor's heat boiled the nearby water until there wasn't enough to slow the neutrons adequately, whereupon the reactor turned off until it cooled enough for the steam to condense. (A. P. Meshik et al., Phys. Rev. Lett. 93, 182302, 2004.)
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