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7-1 2
If these once-through systems are operating on the throwaway option, the fissile
material discharged in their spent fuel elements is deemed unusable; in fact, no value is
assigned to the spent fuel in once-through fuel cycle accounting. Thus, in this case the
most resource-efficient once-through fuel cycle is the one that requires the lowest fissile
charge per unit power. If, however, a capability for reprocessing the spent fuel is
eventually envisioned (i.e., if the throwaway option becomes a stowaway option), then the
quantity of fissile material in the spent fuel becomes an important consideration. Esti-
mates of the amounts of the various fissile materials discharged by each reactor type
operating on both the LEU cycle and the MEU(235)/Th cycle are given in Table 7.2-2.
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Table 7.2.2. 30-Year Charge and Discharge Quanti ties
for Once-Through Fuel Cyclesa
235u
MTIGWe
Fi ssi 1 e Discharge
b
Total
Cumulative
Net Fissile
Reactor Charge 233U 23% Puf Fissile Consumption
PWR
HllR
HTGR
PBR
SSCR
PWR
HWR
HTGR
PBR
24.72
17.53
19.49
18.09
22.25
33.83
32.63
17.99
16.55
LEU Cycle
- 6.45 5.22
- 1.77 5.49
- 3.25 2.16
- 2.79 1.89
. 5.46 5.88
MEU(235)/Th Cycle
7.80 11.52 2.13
14.28 10.08 0.75
2.31 1.35 0.69
2.73 1.17 0.42
a
bAt 75% caDacitv factor.
Estimated from -equilibrium cycle.
11.67 13.05
7.26 10.37
5.41 14.08
4.68 13.41
11.34 10.91
21.45 12.38
25.11 7.52
4.35 13.64
4.32 12.23
For the PUR and HWR, the use of the MEU/Th fuel cycle rather than the LEU fuel
cycle results in a significant increase in the amount of fissile material contained in
the spent fuel. It should be noted, however, that this increase is primarily the result
of higher feed requirements (i-e., 235U commitment). In contrast, converting from the
LEU cycle to the MEU/Th cycle does not materially affect the net consumption of the gas-
cooled HTGR and PBR (although it dramatically affects the types of fissile material pre-
sent in their spent fuel). The relatively low values for the discharge quantities for the
gas-cooled reactors is the result of two effects: a lower initial loading; and a design
that is apparently based on higher burnup, which in turn reduces the amount of fissile
material discharged. Finally, it is to be remembered that the resources represented by the
spent fuel inventory are recoverable only when the spent fuel is reprocessed, whereas the
U308 commitment is necessary throughout the operating lifetime of the reactor. Thus, in a
sense, the spent fuel resource must be discounted in time to order to assess the best system
from a resource utilization basis.
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