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

6.133
Results of a long-term risk comparison (Logan et al. 1980) between a reference (no trans-
mutation) and a transmutation fuel cycle indicate that:
* Cs-137 and Sr-90 would dominate the health effects during the first few hundred years
for both fuel cycles.
* After a few hundred years and for several tens of thousands of years thereafter, the
most significant nuclides for the reference fuel cycle would include a generous mix of
actinides and their daughters at a significantly reduced activity level. Transmutation
would strongly reduce the effects during this period.
* During later years, two nuclides, Tc-99 and 1-129, which are released by leaching, would
completely dominate all other nuclide contributions. Because these nuclides are not
removed through transmutation, the results show no benefit during these later years.
Long-term health effects have been integrated over 1 million years to determine the
long-term probabilistic (expected) risk (Blomaneke et al. 1980 and Logan et al. 1980). The
long-term risk was found to be controlled to a very large extent by the contributions from
Tc-99 and 1-129, which constitute about 99 percent of the integrated risk. This is because
(1) the slow leach incident dominates the long-term probabilistic risk since it was assumed
to have a much higher probability of occurrence than a volcanic or meteor incident and (2)
only those nuclides that sorb poorly or not at all (i.e., iodine, technetium, carbon) mi-
grate through the geosphere quickly enough to reach the biosphere within 1 million years.
Therefore, transmutation of actinides would have its most substantial value if an unlikely
event occurs. For example, the probability of a volcanic incident is only one in 100 bil-
lion, but if it should occur, the radioactive material could enter the biosphere very
rapidly.
Looking at the issue described above in another way, it is noteworthy that catastrophic
events occurring beyond 100 years following emplacement would not cause significant radio-
logic health effects if transmutation where employed.
6.1.7.6 Cost Analysis
The cost of utilizing transmutation to modify the radionuclide composition of waste would
be added to the cost of disposal associated with remaining modified waste. However, modifi-
cation of the waste's radionuclide content has the potential to alleviate some of the dis-
posal requirements and reduce these costs. Such costs have not been developed at this time.
Costs have been developed for a fuel cycle including actinide transmutation utilizing
commercial light water reactors as the transmutation device. These were compared with the
costs of a mixed-oxide fuel cycle (Alexander and Croff 1980). This study indicated cost in-
crease of about 3 percent for nuclear generated electricity if actinide transmutation were
utilized for disposal purposes.
The significant cost differentials were associated with the requirement of specialized
partitioning facilities and hardware. The continued recycle of actinides into the fuel cycle
would increase the neutron activity within the fuel material about tenfold for spent fuel and