Management of Commercially Generated Radioactive Waste - U.S. ...

7.30
7.3.7 Plutonium Disposition
Examination of the disposition of plutonium helps to explain differences in the compo-
sition of the waste produced in the different nuclear growth cases and the effect that the
reprocessing date has on the waste compositions (The reprocessing date effects the amount
of recycle achieved within the time frame of this analysis.) Table 7.3.12 shows the plu-
tonium disposition in both the once-through cycle and the reprocessing cycle. Disposition
in the once-through cycle is straightforward--all of the plutonium goes to the repository
with the spent fuel. With the reprocessing cycle, the situation is more complex. Much of
the plutonium that is recycled is eliminated by fissioning. However, recycle of plutonium
in mixed plutonium and uranium oxide fuel also produces more plutonium by conversion of
238 U. Thus, the total amount of plutonium generated in the reprocessing cycle is always
larger than the total amount of plutonium in the once-through cycle spent fuel. Approxi-
mately 99% of the plutonium in the spent fuel is recovered by reprocessing and (excluding
third-recycle discard) a little more than one percent of the plutonium ends up in the
wastes; approximately 0.5% is in the high-level waste and the balance is dispersed in the
TRU wastes. Plutonium recycle also produces more higher atomic number actinides (e.g.,
anericium, neptunium and curium), which also end up in the waste.
At the end of the reactor operation period in each reprocessing case, there is some
plutonium remaining in the fuel as well as plutonium in the reprocessing pipeline. This
plutonium is shown in Table 7.3.12 as plutonium not recycled. It is assumed to be recovered
by reprocessing but is not recycled in this system. We assume that other reactors that con-
tinue to operate outside of this system would, except for third-recycle plutonium, utilize
this plutonium. Thus, except for the third-recycle portion, the plutonium not recycled is
not considered for disposal in this Statement. Presumably, there will come a time when the
industry will be shut down and the excess plutonium at that time will require disposal.
However, before that time, steps could be taken to minimize the amount of plutonium left in
the pipeline. With proper planning, the amount of plutonium requiring disposal could be
reduced to the plutonium contained in the last batches of spent fuel. Since there would be
no incentive for further reprocessing at that time, this spent fuel could be disposed of as
spent fuel in the same manner as in the once-through cycle.
We assume here that the plutonium recovered from the third recycle is not recycled and
that it is discarded in the high-level waste. Table 7.3.12 shows this to be a relatively
small amount. In a real system, whether or not this plutonium is recycled will be primarily
an economic determination. Recycle could be continued until all of the plutonium is either
fissioned or transmuted to higher actinides, which are then is discarded in the waste.
The two reprocessing dates used for Case 3 illustrate how sensitive the plutonium dis-
position is to reprocessing dates. Less than one-third as much plutonium is recycled when
reprocessing starts in 2010 as when reprocessing starts in 1990. This is because of: 1) the
large inventory of spent fuel accumulated when reprocessing starts, 2) a preference given
to first-recycle plutonium relative to second- or third-recycle plutonium because of its
higher fuel value, 3) the limitation on recycle MOX fuel to 50% of the equilibrium reload