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

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inventory remains essentially constant. The calcine is collected in canisters and residual
water and nitrate are removed by heating to 700°C before the canisters are sealed shut. The
output of the example process amounts to about 0.9 m 3 of calcine per GWe-yr. A smaller
diameter canister may be required for waste calcine than for waste glass to prevent over-
heating at the centerline of the canister, because of the lower thermal conductivity of
calcine.
4.3.2.1 Chemical Partitioning
The partitioning or separation of certain elements from nuclear fuel cycle wastes has
been viewed as a potential means for improving waste management (ERDA 1976, Campbell 1976,
Schneider and Platt 1974, Cooperstein 1976). The perceived benefits result from removal of
certain radionuclides and, hence, improvements in the management of the resulting parti-
tioned radionuclide fraction compared to the management options for the unpartitioned
wastes. Three subsequent options for disposal of partitioned radionuclides are discussed
in this document: 1)_transmutation as discussed in Section 6.1.7, 2) chemical resynthesis
as discussed in Section 4.3.2.3, and 3) space disposal as discussed in Section 6.1.8.
In general, to partition simply means to separate elements, or groups of elements, from
some mixture of chemical species. In a nuclear fuel cycle, partitioning would occur mainly
during the reprocessing of spent fuel (ERDA 1976). There are many chemical elements in
spent nuclear fuels (see Section 2.1), and many combinations in which these elements may be
chemically separated. Consequently, there are also numerous partitioning alternatives that
may facilitate useful waste treatment alternatives or disposal options. For all the speci-
fic partitioning candidates described here, one must realize that: 1) no partitioning
processes have been demonstrated for waste disposal on a commercial scale; 2) historically
most recovery processes leave several percent, or more, of the desired elements in the waste
streams; and 3) partitioning for waste management purposes requires substantially higher
recoveries than have been achieved to date. Partitioning itself is not an option for final
disposal of radioactive wastes, although some waste partitioning may be required as a
pretreatment to permit the final disposal of the resulting waste fraction (e.g., the parti-
tioning of fission product iodine for space disposal).
With respect to waste management, partitioning may lead to improved waste characteris-
tics for either the short term (less than 1000 years) or the long term (greater than
1000 years). The partitioning of strontium and cesium, for example, may be a useful option
to reduce the self-heating (Buckingham 1967) characteristics of high-level wastes over the
short term and thereby permit the storage of salt cakes that are not overly self-heating.
In addition, the partitioning of actinides as well as some fission products may be useful to
reduce the long-term radiotoxicity of wastes (Bond and Leuze 1975, Croff et al. 1977) and,
therefore, reduce the exposure of future populations to radioactivity should the wastes ever
be reintroduced into man's environment in the distant future (say after 100,000 years of
storage).