Environmental Engineering Reference
In-Depth Information
which has very low radioactivity and is not radioactive
enough to be of concern. It could even be put back in
the mines from which the original ore came.
There is no scienti
c or engineering dif
culty in deal-
ing with
fission fragments (FF), the next most abundant
component. Though very highly radioactive when they
come out of a reactor, the vast majority of them have to be
stored for only a few hundred years for radioactive decay
to reduce the hazard to negligible levels. Robust contain-
ment that will last the required time is simple to build.
The pyramids of Egypt have lasted more than
years
and there is little argument about our ability to do at least
that well. There are two long-lived FFs, iodine-
and
technetium-
. They can be treated in the way the long-
lived components are treated.
The problem comes from that last
% of the spent fuel,
composed of plutonium (Pu) and the elements called
the minor actinides, neptunium (Np), americium (Am),
and curium (Cm). The four are collectively known as the
transuranics or TRU. Though they are much less radio-
active than the FF, they are dangerous and have lifetimes
about
times greater. Instead of isolation for hun-
dreds of years, isolation for hundreds of thousands of
years is needed. There is a second way to protect the
public from this material, transmutation by neutron bom-
bardment to change the TRU into shorter-lived
fission
fragments, but this is not yet out of the development stage.
Long-term isolation is the principle behind the
“
once-
through
”
system, advocated by the United States from the
late
s until recently as a weapons-proliferation con-
trol mechanism; the policy was adopted in
by the
Carter Administration. In once-through all the spent fuel
