Environmental Engineering Reference
In-Depth Information
Technical Note . : Producing Material
for Weapons
Uranium: All LWRs use enriched uranium where the
amount of the
fissionable isotope U-
is increased from
the naturally occurring fraction of
.
% in uranium ore to
% depending on the design of the reactor. This
enrichment process (the front end of the fuel cycle) is of
concern because of the potential to enrich far beyond the
requirement for power production to the level needed
to make a nuclear weapon. Although anything enriched to
greater than
%to
is considered weaponizable, in
reality any state or group moving toward a weapon will want
material enrichment to the
%U-
% level. It is much easier to
make a weapon at this enrichment than at
% enrichment.
If a facility is doing the enrichment required for a power
plant, it takes only a small increment in capacity to produce
the material for a few uranium weapons. Some numbers are
useful to understand the problem. Most of the nuclear plants
being built now use
-
% enriched uranium. A
GWe
nuclear plant requires about
kg of new enriched fuel
per year. Because natural uranium contains much less than
isotope, nearly ten times as much natural
uranium is required to make that much enriched fuel.
However, only about
.
% of the U-
kg of the
.
% enriched material
is needed as input to make the
% enriched material for a
single weapon.
As described earlier, the preferred technology for enrich-
ment now is the gas centrifuge. A cylinder of gas (uranium
hexa
uoride) containing both U-
and U-
is spun at
very high speed. The heavier U-
tends to concentrate
more at the outside of the cylinder so gas taken off from near
the center is slightly enriched in U-
. Since the enrich-
ment is slight at each stage, a multistage cascade of centri-
fuges is needed to enrich to the level needed for reactor fuel.
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