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

N.3
operation used to separate the fuel from the structural material. In this amount a system
might be required to remove 14 C from the reprocessing facility off-gas stream.
Because of high radioactivities, the isotopes 232 U and 228 Th incidentally generated in
the 232U-thorium cycle pose some short-term handling problems not significantly present with
the SEU system. Uranium-232 has a 70-year half-life followed by much shorter half-lived
daughters leading to 208 T1, which has a 2.6 MeV gamma. In the recycle case, this compli-
cates the handling of 233 U fuels even though it is present in only a few parts per million.
However, as a diluent in uranium, it does not appreciably complicate waste storage. A long-
term concern may be the precursor of 232 U, namely 231Pa. The concentration in the wastes
of 23 1 Pa with its 32,500-year half-life will depend on how it is managed in the successive
recycle. There is, of course, an incentive to hold the protactinium in a processing vessel
to assure that the 233 Pa fully decays to 233 U, which is then bled off and recycled. Under
these circumstances there is no reason to recycle protactinium and thus 23 1 Pa is not "burned
out." Its concentration in the wastes is correspondingly increased to levels that may
approach the 23 9 Pu concentration in wastes from plutonium recycle. This could be allevi-
ated by purposefully irradiating 23 1 Pa as an isolated target and by adding the 232U gener-
ated into the high-level wastes in dilutions so localized heating will not be produced.
Currently it is believed necessary to add fluorine to dissolve spent thorium oxide
fuel. The effects of fluorine, if any, upon the waste processing are unknown. However,
steps could be taken to obviate the fluorine in the processing. This may involve addition
of magnesium, calcium, or other elements to thorium oxide which will add to waste volume,
but not appreciably to radioactivity. This may, however, increase the solubility of
thorium dioxide in water coolant streams, increasing contamination of water coolant streams
if fuel jackets develop leaks.
It is not believed that fluorine will detract from the qualities of the waste glass as
fluoride is a constituent of many commercial glasses and enamels. The fluorine content of
commercial glasses rarely exceeds 6%. Fluoride at those high concentrations acts as an opacifier
in the glass owing to dispersed fluoride crystals. considerable laboratory experimentation
has already been done on the incorporation of fluoride in nuclear waste glass.