ORNL-5388 - the Molten Salt Energy Technologies Web Site

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Introduction dates for each reactor type are included in Table 6.1-2. A slight modifica-
tion to an existing PWR fuel design, such as a thicker fuel pin cladding to extend the dis-
charge exposure, was introduced in 1981. A more extensive modification, such as a denatured
235U PWR fuel pin, was delayed until 1987. The remaining PWR designs, including the SSCRs,
were introduced in 1991.
were not introduced until 2001.
The HWRs and HTGRs were all introduced in 1995, while the FBRs
The lifetime-averaged 233U, 235U, and fissile plutonium flows given in Table 6.1-3 show
that for the throwaway cycle, low-enriched HTGRs offer significant (alwxt 20%) uranium ore
savings compared to low-enriched PWRs.
Slightly enriched HWRs reduce uranium ore require-
ments by an additional 20% over HTGRs and more than 35% over LWRs.
Although low-enriched
LWRs and HTGRs have roughly the same enrichment requirements, the slightly enriched HWRs
require 5 to 6 times less enrichment. The low-enriched SSCR offers about a 22% savings in
enri chmen t .
Core discharge exposures for FBRs are approximately twice the exposures for LWRs,
while exposures for HWRs are about half those for LWRs.
An exception is the natural-
uranium HWR, which has a discharge exposure of one-fourth that for the LWR.
HTGR dis-
charge exposures are extremely large - nearly 200 MWd/kg for the Pu/Th fuel design!
The two FBRs with Pu-U cores have breeding ratios of 1.34 to 1.36. Replacing the
uranium in the core with thorium reduces the breeding ratio by 0.15, while replacing the
plutonium with 233U reduces the breeding ratio by 0.16.
thermal reactors with 233U-fueled reactors shows that the 233U-fueled reactors have con-
version ratios about 0.10 to 0.15 higher.
shown
fueled
Finally, comparing 235U-fueled
The most striking observation that can be made from the total fissile fuel requirements
n Table 6.1-3 is the significantly lower fissile requirements for the denatured 233U-
SSCRs and HWRs and for the highly enriched 233U/Th-fueled HTGR.
Finally, a few comments should be made about the relative uncertainties of the per-
formance characteristics for the reactor designs in this study. Clearly, the low-enriched
235U-fueled LWR (PblR) has low performance uncertainties. Numerous PWRs that have been designed
using these methods are currently in operation. The highly enriched 235U-fueled HTGR also
would be expected to be quite accurate since Fort St. Vrain started up in 1977. For the same
reason, the successful operation of HWRs in Canada gives a high level of confidence in the
natural uranium fueled CANDUs.
The Pu-U-fueled FBRs have had a great deal of critical experiment backup, and a few
FBRs have been built in the U.S. and abroad, giving assurance in the calculated performance
parameters of these reactors. Most of the remaining reactors, however, have rather large
uncertainties associated with their performance characteristics. This is because these
reactors have not been built, and most have not even had critical experiments to verify the
designs.
The uncertainty for the alternate-fueled reactor designs is even greater since the
effort in developing nuclear data for 233U and thorium has been modest compared to that
expended in developing data for 235U, 238U, and plutonium.