Environmental Engineering Reference
In-Depth Information
Technical Note . :
(cont.)
When spent fuel comes out of a reactor, the radiation is so
intense that some form of cooling is required to keep the
fuel rods from damage that would lead to the escape of
radioactive material. They are put into cooling ponds where
enough water circulates by natural convection to keep the
temperature of the rods at a safe level. Typically, practice is
to keep the fuel in the ponds for at least
years. The
radioactivity and the associated heat generated have, by
then, decayed enough to allow the rods to be removed from
the ponds and put into dry casks for storage or shipped off
site if so desired. If removed from the ponds, containers
have thick enough shielding that the material can be safely
stored above ground with no danger from radiation. The
intense radiation from the
fission fragments in the spent fuel
acts as a barrier to theft or diversion. Since any would-be
thief would receive a disabling and lethal radiation dose in a
matter of minutes, the spent fuel including its plutonium is
thought to be safe.
The spent fuel can be reprocessed to extract the pluto-
nium and reuse it to generate more energy in power react-
ors. The chemical process used is called the PUREX process
and is well-known chemistry; there are no secrets to learn.
This is the process that North Korea used to extract the
plutonium from the spent fuel from their Yongbyon reactor
to get material for their weapons program. There are really
two periods in the life-cycle of spent fuel with different
proliferation vulnerabilities. The
first period is while it is in
the cooling pond at each reactor. The second period is after
the radioactivity of the spent fuel has decayed to the point
where it can be removed from the cooling pond. I separate
things this way because there is no way as yet to move spent
fuel from a cooling pond until its radioactivity has decayed
enough that it can be moved with passive cooling, so there is
a period when the spent fuel with its plutonium remains
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