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

6.1.7.1 Concept Summary
6.119
6.1.7 Transmutation
The primary goal of waste disposal has been stated as protection of the public. This
would be achieved in mined geologic disposal by containing the high-level radioactive waste
for the time period during which it retains significant quantities of potentially harmful
radionuclides. One alternative to this approach is to selectively eliminate the long-lived
radionuclides by converting or transmuting them to stable or short-lived isotopes. This ap-
proach would shorten the required containment period for the remaining waste. Shortening the
containment period would increase confidence in predicting the behavior of the geologic media
and reduce the requirements on the isolation mechanism. Thus, an attractive feature of
transmutation is that it has the potential to reduce the long-term risk to the public posed
by long-lived radionuclides.
In the reference transmutation concept, spent fuel is reprocessed to recover the uranium
and plutonium. The remaining high-level waste stream is partitioned into an actinide stream
and a fission product stream. The fission product stream is concentrated, solidified, vitri-
fied, and sent to a terrestrial repository for disposal. In addition, actinides are parti-
tioned from the TRU-contaminated process waste streams from both the fuel reprocessing plant
and the mixed oxides fuel fabrication plant. The waste actinide stream is combined with
recycled uranium and plutonium, fabricated into fuel rods, and reinserted into the reactor.
For each full power reactor year, about 5 to 7 percent of the recycled waste actinides are
transmuted (fissioned) to stable or short-lived isotopes. These short-lived isotopes are
separated out during the next recycle step for disposal in the repository. Numerous recycles
result in nearly complete transmutation of the waste actinides.
A disposal system that uses transmutation would have the environmental and health impacts
associated with the recycle of uranium and plutonium and with the partitioning of the actinides
from the waste stream. If uranium ahd plutonium recycle were adopted for other reasons
transmutation would be more feasible but would still involve additional impacts. For exam-
ple, highly radioactive fuel elements containing recycled waste actinides would need to be
fabricated, handled, and transported. The additional facilities and waste treatment proces-
sing steps required could be expected to increase effluent releases to the environment, the
occupational exposure, the risk of accidents, and costs. Since only about 5 to 7 percent of
the recycled waste actinides would be transmitted to stable isotopes in each reactor irradia-
tion, numerous recycles would be required with attendant additional waste streams.
6.1.7.2 System and Facility Description
System Options
The reference concept was selected from several available options. These options are
listed in Figure 6.1.20 for each major step in a flowsheet using transmutation.