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

4.22
methods described in Chapter 6 as alternatives to geologic disposal. However, two of these
alternative disposal methods (rock melting and well injection) involve disposal of the high-
level waste in liquid form; thus, a modified spent fuel treatment process is required.
Application of these methods to disposal of dissolved spent fuel presents added nuclear
criticality safety problems and feasability uncertainties resulting from the presence in the
solution of all of the plutonium and the uranium.
By eliminating the calcination and vitrification operations, the spent fuel treatment
process described in Section 4.3.1.3 could provide a liquid waste stream for disposal.
Additional storage would probably have to be provided for the dissolved spent fuel solution
to allow proper operation of the disposal process, however. A flow diagram for such a pro-
cess is shown in Figure 4.3.4.
4.3.2 High-Level Liquid Waste Treatment
High-level liquid wastes are defined as "those aqueous wastes resulting from the opera-
tion of the first cycle solvent extraction system, or equivalent, and the concentrated
wastes from subsequent extraction cycles, or equivalent, in a facility for reprocessing
irradiated reactor fuels" (10 CFR 50). These wastes contain over 99% of the nonvolatile
fission products and actinides, except U and Pu. If spent fuel is reprocessed, the U and
Pu will normally be recycled. Only a small amount of U and Pu, perhaps 0.5%, resulting from
waste losses during reprocessing will be in the HLW. Liquid high-level waste can be stored
in tanks as an interim measure, but it must be solidified before transportation and
disposal.
Many HLW treatment processes are under development and DOE is committed to examining
the relative merits of many of these processes. For this discussion the candidate processes
have been divided into three categories: those that convert the HLW into glass (Sec-
tion 4.3.2.2), into a crystalline solid (Section 4.3.2.3), or into a composite or multiphase
solid form (Section 4.3.2.4). A further important distinction concerning the candidate HLW
waste treatment processes should also be made. The processes fall into two broad classes:
those that have been developed to the stage of practical engineering-scale implementation,
and those for which there has been some characterization of waste form properties but little
or no process development. Calcine, low-melting glass and cement can be placed in the first
category. All of the rest of the waste forms to be described fall into the latter, rela-
tively undeveloped category. Additional data on many of these processes may be found in
ERDA-76-43.
The processing descriptions given here assume that the HLW is not partitioned before
treatment; however, because chemical partitioning has potential as a pretreatment for
high-level liquid waste, partitioning techniques are also discussed in this section.
Before proceeding with the more general discussion, brief descriptions will be given of
the two well developed high-level liquid waste treatment processes used in this Statement
for evaluation of environmental impacts and costs. These processes are: