ORNL-5388 - the Molten Salt Energy Technologies Web Site

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required 233U makeup).
7-1 5
plutonium contained in the discharged fuel , which is obviously desirable from a safeguards
viewpoint.
Increasing the 233U enrichment also reduces the amount of fissile
However, increasing the 233U fraction also increases the vulnerability of the
denatured fuel to isotopic enrichment, effectively forcing a compromise between prolifera-
tion concerns regarding the fresh fuel versus proliferation concerns regarding the spent fuel.
The lowest enrichment feasible for the denatured LMFBR systems analyzed :iez in the range
of 11-14%. Such a system would utilize U02 as fuel and would require significant amounts
of 233U as makeup since the plutonium it produced could not be recycled into it.
The "breeding" ratio components of certain denatured LMFBRs as a function of 233U
f
enrichment are shown in Table 7.2-5. The ratio of 233U produced to Pu produced is very
sensitive to the specified degree of denaturing in the range of 12-20% 233U/U.
gests that significant performance improvements may be possible (i .e. , increased 233U produc-
tion and decreased 239Pu production) for relatively small increases in the denaturing
criteria.
degraded below that for the reference P U / ~ ~ cycle ~ U (see Table 4.5-1 in Chapter 4).
This sug-
Of course, the overall "breeding" ratio of the denatured LMFBR is significantly
Table 7.2-5. Denatured LMFBR Mid-Equilibrium Cycle
Breedi ng Ratio Components*
23311 233U "Breeding" Pu "Breeding" Overall "Breeding"
En r i c hmen t Component Component Ratio
%12% 0.41 0.71 1.12
20% 0.70 0.39 1.09
40% 0.90 0.15 1.05
100% 1.02 - 1.02
*Using values from Section 4.5-1. A more recent study [Prolifera-
tion Resistant Large Core Design Study (PRLCDS)] indicates that
substantial improvements in the FBR performance is possible.
Because of the superior breeding potential of a 239Pu-fueled system relative to a
233U-fueled system in a fast neutron spectrum, the fast reactor is ideally suited to the
role of a plutonium-fueled transmuter. Moreover, in contrast to the thermal trsnsniuters,
the fast reactors result in a net overall fissile material gain.*
Two types of FBR transmuters have been analyzed for the classical homogeneous FBR
core configuration (a central homogeneous core surrounded by fertile blankets).
first, the usual Pu/238U-fueled core was assumed with a Tho2 radial blanket (also a Tho2 axial
blanket in one case).
the net production data for typical fast transmuters of each type. The overall fissile
gain/cycle with the core is significantly higher than that with the Pu/Th core,
the result being that the "breeding" ratio is not noticeably reduced from the breeding
ratio for the reference cycle. The production of 233U in the Pu/Th reactor is
approximately a factor of 4 higher, but this is achieved as a result of "sacrificial"
consumption of plutonium.
In the
In the second type a Pu/Th core was assumed. Table 7.2-6 summarizes
Thus, these two reactor types reflect a tradeoff between 233U
As noted in Chapter 4.5, significant uncertainties are associated with the fast-neutron
cross sections for 233U and Th.