A prehistoric natural "nuclear reactor", which was in operation about 2
billion years ago, was discovered in the uranium
deposit of Oklo in Gabon in 1972. Subsequently, further locations in this
deposit were found where a self-perpetuating chain
reaction must have taken place due to the reduced U-235 content in the
natural uranium. Of the 17 known fossil
reactors, 9 have been completely mined out. For the Oklo II location, it
can be calculated from the depletion of uranium-235 entailed by fission
that a minimum of 4 tonnes of U-235 must have been fissioned, 1 tonne of
Pu-239 formed, and a volume of heat of about 100 billion kWh generated.
As a comparison: in the reactor of a nuclear power plant of the 1,300 MWe
category, about 30 bn kWh heat is generated by fission annually.
|One of the fossil reactors at Oklo. Uranium oxide
remains are visible as the yellowish rock.
Oklo by-products are being used today to probe the stability of the fundamental
constants over cosmological time-scales and to develop more effective means
for disposing of human-manufactured nuclear waste.
AND NUCLEAR PHYSICS
Source: European Nuclear Society