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a significant increase in burnup over the current design would require mechanical design
modifications.
The thermal efficiency can be improved by increasing the coolant pressure. This
would require stronger pressure tubes and thus penalize the neutron economy. The use of
enriched fueling could result in a higher power peaking factor, which would require a re-
duced linear power rating, unless an improved fuel management scheme is developed to re-
duce the power peaking factor.
Scoping calculations have been performed to address possible design modifications
for CANDU fuel cycles other than natural ~ranium,”~ and detailed design tradeoff and
optimization studies associated with the enriched fuel cycles in CANDUs are being carried
out by Combustion Engineering as a part of the NASAP program. In the study reported here,
in which only the relative performance of the denatured 233U cycle is addressed, the currentgeneration
1200-MWe CANDU .fuel design presented in Table 4.3-1 was assumed for all except
the natural-uranium-fueled reactor. A discharge burnup of 16,000 MWD/T (which is believed
to be achievable with the current design) and the on-line refueling capability were also
assumed.
The fuel utilization characteristics for various fuel cycle options, including the
denatured 233U cycle option, were analyzed at Argonne National Laboratory5 and the results
are sumnarized in Table 4.3-2. Some observations are as follows:
1. Natural-Uranium Once-Through Cycle: In the reference natural uranium cycle,
the 30-yr U308 requirement is about 4,700 ST/GWe, which is approximately 20% less than
the requirement for the LWR once-through cycle. Even though the fissile plutonium
concentration in the spent fuel is low (4.27%).
discharged annually is twice that from the LWR.
the total quantity of fissile plutonium
2. Slightly-Enriched-Uranium Once-through Cycle: With slightly-enriched uranium
(1% 235U), a 16,000-MWD/T burnup can be achieved and the U308 consumption is reduced by
25% from the natural-uranium cycle. As shown in Fig. 4.3-1, the optimum enrichment is
in the area of 1.2%, which corresponds to a burnup of about 20,000 MWD/T.
3. Pu/U, Pu Recycle: In this option, the natural uranium fuel is “topped” with
0.3% fissile plutonium. A discharge burnup of 16,000 MWD/T can be achieved and the plu-
tonium content in the discharge is sufficient to keep the system going with only the
natural-uranium makeup. The U308 requirement is reduced to about one half of that for
the natural-uranium cycle. (Smaller plutonium toppings decrease the burnup and make the
system a net plutonium producer; larger toppings increase the burnup and make the system
a net plutonium burner.)