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

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APPENDIX N
WASTES FROM THORIUM-BASED FUEL CYCLE ALTERNATIVES
A number of thorium-based fuel cycle alternatives to the light water uranium-plutonium
cycle have been proposed. The alternat*i# il ude,: the uniform enrichment of thorium in
LWR and heavy water; spike blanket systems -in-tEWRs; crossed progeny in LWR's heavy water and
fast converters; light water breeder (LWBR); and high-temperature gas-cooled reactor (HTGR)
fuel cycles. For this Statement the LWBR and HTGR cycles have been chosen for discussion
because their demonstration is nearer completion. Thus, they may be the first systems able
to employ a thorium load. Moreover, a standard LWR using a thorium fuel cycle will have
fission-product yields very similar to those of the LWBR. Analyses for managing wastes from
these thorium fuel cycles have not been made in as great detail as for the LWR uranium
cycles presented elsewhere in this Statement. The basis for this discussion is DOE/ET-0028,
and that document should be 'referred to for a more-complete presentation.
As in the slightly enriched light water reactor cycle, power reactors could use thor-
ium in either recycle or nonrecycle modes. In the recycle mode, spent fuel is reprocessed
to remove fissionable 2 3 3 U that has been generated and to remove the initial fissionable
species that remains unburned from the irradiation.(a) This material (mostly bred 23 3 U) can
then be refabricated into fuel elements for reinsertion into a nuclear power reactor. This
can be accomplished whether or not the amount of'fissile material generated is large enough
for the reactor to constitute a true breeder, which, once started, provides its own fission-
able fuel. The system may not be operated as a breeder, but even so, the fissionable mate-
rial required for makeup (235U, plutonium, 23 3 U from other sources) may not be large.
In the nonrecycle mode, the fissionable material generated is not returned to the core,
either because the fuel is not reprocessed or because the product from the reprocessing
plant is treated as waste or is stored for future use. In this case, new fissionable
material would be supplied for each core loading.
In the discussion that follows, wastes from the reprocessing of thorium fuels from
LWBR and HTGR are compared with those from commercial light waste reactors (LWRs). It is
assumed that 99.5% of the plutonium is separated from the LWR waste in reprocessing, but is
not recycled. All comparisons are based on production of equal quantities of electrical
energy.
(a) Under DOE management directives it is mandatory that 23 3 U and 2 3 9 pu be disposed of in a
imilar manner. The reasoning for this is not because of any near-term risk from the
33U but because of the higher specific toxicity of the daughter products in the long
term.