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3-8
The values in Table 3.1-2 are a result of a standard HTGR fuel composition which
has an average Th/233U ratio of about 20. Preliminary estimates have been made of dena-
tured HTGR fuels which assume a 20% denatured 235U, leading to a 15% denatured 233U.6
Because of the added 2381) fertile material, the amount of thorium is correspondingly re-
duced by about 30%, resulting in a similar reduction in the 232U production. The con-
centration of 232U in total uranium would also be reduced by the mere presence of the
diluting 238U, so that it can be estimated that a 15% denatured 233U HTGR would contain
approximately 40 ppm 232U in uranium after equilibrium recycle. The lower 232U levels
in the HTGR are primarily due to a softening of the neutron energy spectrum compared with
that of the LWR. This results in a marked reduction in the 232Th(n,2n') reaction rate,
which is a prime source of 232U.
3.1.3. Fast Breeder Reactor Fuels
232U concentrations calculated by Mann and Schenter' and by Burns8 for various
Except for Case 2, tnese
conunercial-sized FBR fuel cycles are given in Table 3.1-3.
values were determined from reacti on-rate cal cul ati ons using 42 energy groups and one-
dimensional geometry; the Case 2 results were determined from a coarse nine-group two-
dimensional depletion calculation.
It is important to note that Cases 1 and 2 represent the "transmuter" concept. All
the discharged uranium (23211, 233U, 2s4U, and 235U) is bred from the 232Th initially
charged and consists principally of 2331).
will be reduced by a factor of 5 to 8 in the denatured fuel manufactured from this mate-
rial.
approximately 150-750 ppm 23211 in uranium.
This accounts for the high 232U/U ratio, which
Thus, denatured fuel generated via the fast Pu/Th transmuter is expected to have
Case
NO. Fuel
Table 3.1-3. FBR Core Region 232U Discharge Concentrations'
2321) in u (PP~)
t=lyrb t = 2 y r t = 3 y r t = 5 y r
No recycle
1 10% 239Pu in Th 982 1710 2380 3270
2 11% 239Pu i n Th 1106 2376 3670
3 10% 233U in Th 288 830 1330 221 0
4 10% 2331) in 238U 6.6 10.7 12.5 13.3
With recycle
5 10% 233U in Th 1820 2760 3260
6 10% 23311 in 23% 35 35 35
aCases 1, 3-6 are from ref. 7; Case 2 is from ref. 8.
bt = fuel residence time for no recycle cases; t = burning time before recycle for
recycle cases.
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