Oklo: A Natural Nuclear Reactor
Modern deposits of uranium contain only up to ~0.7% 235U (and ~99.3% 238U), which is not enough to sustain a chain reaction moderated by ordinary water. But 235U has a much shorter half-life (700 million years) than 238U (4.5 billion years), so in the distant past the percentage of 235U was much higher. About two billion years ago, a water-saturated uranium deposit (in what is now the Oklo mine in Gabon, West Africa) underwent a naturally occurring chain reaction that was moderated by groundwater and, presumably, controlled by the negative void coefficient as the water boiled from the heat of the reaction. Uranium from the Oklo mine is about 50% depleted compared to other locations: it is only about 0.3% to 0.7% 235U; and the ore contains traces of stable daughters of long-decayed fission products.
Read more about this topic: Nuclear Reactor Physics
Famous quotes containing the words natural and/or nuclear:
“When a natural discourse paints a passion or an effect, one feels within oneself the truth of what one reads, which was there before, although one did not know it. Hence one is inclined to love him who makes us feel it, for he has not shown us his own riches, but ours.”
—Blaise Pascal (1623–1662)
“American universities are organized on the principle of the nuclear rather than the extended family. Graduate students are grimly trained to be technicians rather than connoisseurs. The old German style of universal scholarship has gone.”
—Camille Paglia (b. 1947)