ORNL-5388 - the Molten Salt Energy Technologies Web Site

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2.2. THE DENATURED 233U FUEL CYCLE
In the denatured 233U cycle, the fresh fuel would consist of a mixture of fissile 233U
diluted with 23eU (the denaturant) and combined with the fertile isotope thorium. The pre-
sence of a significant quantity of 23eU denaturant would preclude direct use of the fissile
material for weapons purposes even if the uranium and thorium were chemically separated. As
in the LEU cycle, an additional step, that of isotopic enrichment of the uranium, this time
to increase its 233U concentration, would be necessary to produce weapons-grade material ,
and the development of an enrichment capability would require a significant decision and com-
mitment well in advance of the actual diversion of fissile material from the fresh fuel.
This is in contrast to the reference Pu/U fresh fuel for which only chemical separation would
be required. Moreover, even if such an enrichment capability were developed, it would ap-
pear that enriching clandestinely obtained natural uranium would be preferable to diverting
and enriching reactor fuel, whether it be denatured 233U or some other type, since the reactor
fuel would be more internationally "accountable."
The primary advantage of the denatured fuel cycle is the inclusion of this "isotopic
barrier" in the fuel. Whereas ir, the plutonium cycle no denaturant comparable to 238U exists
and the fresh fuel safeguards (that is, physical security, international monitoring, etc.)
would all be external to the fuel, the denatured 233U fuel cycle would incorporate an in-
herent safeguard advantage as a physical property of the fuel itself. Like the plutonium
cycle, the denatured fuel cycle would require the development of fuel cycle centers to
safeguard sensitive fuel cycle activities such as reprocessing (but not necessarily refabri-
cation). However, unlike the plutonium cycle, the denatured fuel cycle would not require
the extension of such stringent safeguard procedures to the reactors themselves, and they
are the most numerous component of the nuclear fuel cycle.
"denatured" in the sense that a low concentration of 23% is included in a 23'3U matrix.
Similarly, natural uranium fuel is denatured.
resistance advantages of the isotopic barrier.)
(As noted above, LEU fuel is also
Thus, these fuels also have the proliferation-
The concept of denatured 233U fuel as a proliferation-resistant step is addressed
principally at the front end of the nuclear fuel cycle, that is, the fresh fuel charged
to reactors. The 238U denaturant will, of course, produce plutonium under irradiation.
Thus, as in the LEU and mixed oxide cycles, the spent fuel from the denatured cycle is a
potential source of plutonium. However, also as in the LEU and mixed oxide cycles, the
plutonium generated in the spent fuel is contaminated with highly radioactive fission products.
Moreover, the quantity of plutonium generated via the denatured fuel cycle will be signif-
icantly less than that of the other two cycles. Further, the decision to use spent
reactor fuel as a source of weapons material requires a previous commitment to the develop-
ment of shielded extraction facilities.
In sumnary, the use of a denatured fuel as a
source of weapons material implies one of two strategic decisions:
the development of an
isotopic enrichment capability to process diverted fresh fuel, or the development of a, fisc
sile extraction capability (chemical or isotopic) to process diverted spent fuel.
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