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natural reactor




Reference: Introductory Nuclear Physics
by Kenneth S. Krane
section 13.8: A Natural Fission Reactor

The French discovered the low abundance of
235U in samples from Oklo on the west coast
of Africa, initially only 3 standard deviations
below the 0.72%.  Further sampling showed lower
235U abundances, as low as 0.44%!  A rough
estimate calculated about 5 tons of 235U were
fissioned.  Of course, the reaction started back
when the abundance was high enough to sustain
a reaction (somewhere around 3% is about 2 billion
years ago!)  More interesting is that the reaction
was moderated by the groundwater, and for the deposits
to form, the U was probably transported there by
as UO2 +2 ions.

The fission products have migrated very little, still
in place in the reactor zone.  This suggests that
there is merit in the idea of burying waste in
geologically stable formations.  In fact, one of the
biggest criticisms of ground waste storage is the
possibility of transport via the ground water.  And this
exposure pathway seems to have been demonstrated
neglible in the case of this natural reactor, even
after severl billion years!

John Stephens
an aspiring HP grad who's still unemployed...