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optimized for high conversion; rather it is a Pu burner designed for low fuel cycle costs.
A Pu/Th case designed for high 233U production would have a C/Th ratio for the equilibrium
cycle of 430 rather than 650 as in Case 5 (ref. 5).
In Case 6 the feed is fully enriched (93%) uranium and thorium and no recycle is allowed.
Such a system would provide the means for generating a potential stockpile of 233U in the
absence of reprocessing capability. If 233U recycle is not contemplated, the economical optimum
once-through cycle would have a lower thorium loading (C/Th = 330).
Case 7 involves the use of highly enriched 23% and uranium recycle. The heavy fer-
tile loading (C/Th = 150) results in the high conversion ratio (and high initial fissile
loading requirement) shown in Table 4.4-1.
Case 8 involves the use of fully enriched (93%) uranium and thorium designed for
recycle conditions. This is included as the pre-1977 reference high-gain HEU(235U)/Th
recycle case for comparison with the other above cases.
Both GA and ORNL have performed mass balance calculations for an HEU(235U)/Th fuel
cycle with uranium recycle.2,6 These calculations were for a 1160-MWe plant with a power
density of 8.4 Wt/cm3 and a C/Th ratio for the first core and reload cycles of 214 and
238 respectively.
(for a capacity factor of 75% and an assumed tails enrichment Of 0.2 w/o) of 2783 ST U308/
GWe and 2778 kg SWU/GWe, respectively.
The GA results indicate cumulative U308 and separative work requirements
are 2690 ST U308/GWe and 2684 kg SWU/GWe.
Comparison of these results with the same case without recycle (Case 6, Table 4.4-1) shows
a U308 savings of ~38% if uranium is recycled.
The corresponding results for the ORNL calculations
As can be seen, the agreement is fairly good.
It is conventional to compare 30-yr cumulative U308 and separative work requirements
for different reactor types on a per GWe basis with an assumed constant capacity factor.
The results reported in Table 4.4-1 were generated for an assumed variable capacity factor
which averaged 65.9% over the 30-yr life. To facilitate comparison with U3O8 requirements
in other sections of Chapter 4, estimated 30-yr requirements for a constant capacity factor
of 75% have also been included in the table. These values were obtained by applying a
factor of 0.750/0.659 to the calculated requirements for the variable capacity factor.
Obviously this technique is an approximation but it is fairly accurate.
ments for a 75% capacity factor for Case 8 were explicitly calculated and not obtained by
the above estimating procedure.
The 30-yr require-
As is indicated in Table 4.4-1, the MEU(2O% 235U)/Th no-recycle case is more re-
source efficient than the LEU no-recycle case.
able in HTGR fuels and the high in situ utilization of 233U.
through MEU(2O% 235U)/Th cycle requires significantly more U308 than the once-through LEU
cycle. Thus MEU(20% 235U)/Th fuels in HTGRs are an attractive option for stowaway cycles
in which 233U is bred for later use.
This results from the high exposure attain-
In water reactors, the once-
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