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4.5. LIQUID-METAL FAST BREEDER REACTORS
T. J. Burns
Oak Ridge National Laboratory
A preliminary analysis of the impact of denatured fuel on breeder reactors was
performed by Argonne National Laboratory, Hanford Engineering Development Laboratory,2
and Oak Ridge National Laboratory3 for a variety of fissile/fertile fuel options.
analysis concentrated principally on oxide-fueled LMFBRs due to their advanced state of
development relative to other potential breeder concepts.
Table 4.5-1 summarizes some of the significant design and performance parameters
for the various LMFBR designs considered. The procedure followed by each analysis group
in assessing the impact of alternate fuel cycles was essentially the same.
The
A reference
design (for the Pu/~~*U cycle) was selected and analyzed, and then the performance para-
meters of alternate fissile/fertile combinations were calculated by replacing the refer-
ence core and blanket material by the appropriate alternative material (s).
As indicated by Case 1 in Table 4.5-1, a different reference design was selected
by each group, emphasizing different design characteristics. The three basic designs do
share certain characteristics, however. Each is a "classical" LMFBR design consisting of
two core zones of different fissile enrichments surrounded by blankets (axial and radial)
of fertile material. In assessing the performance impact of various fissile/fertile com-
binations, no attempt was made to modify or optimize any of the designs to account for
the better thermophysical properties (e.g., me1 ting point, thermal conductivity, etc.)
of the alternate materials relative to the reference system. (Note: The question of
selection and subsequent optimization of proliferation-resistant LMFBR core designs is
currently being addressed as part of the more detailed Proliferation-Resistant Core
Design study being carried out by DOE and its contractor^.)^
In all cases ENDF/B-IV nuclear data5 were utilized in the calculations. The ade-
quacy of these nuclear data relative to detailed evaluation of the denatured fuel cycle
fast systems is open to some question. Recent measurements of the capture cross section
of 232Th,6 the primary fertile material in the denatured fuel cycle, indicate significan
discrepancies between the measured and tabulated ENDF/B-IV cross sections for the energy
range of interest. Additionally, the adequacy of the nuclear data for the primary de-
natured fissile species, 233U, for the LMFBR spectral range has also been questioned.'
Due to these possible nuclear data uncertainties and also to the lack of design optimiza-
tion of the reactors themselves, it is prudent to regard the results tabulated in
Table 4.5-1 as preliminary evaluations, subject to revision as more data become available.
The compound system fissile doubling time given in Table 4.5-1 was calculated using
the simple approximation that
C.S.D.T =
0.693 s (Initial Core + Eq. Cycle Charge)
(RF x Eq. Cycle Discharge - Eq. Cycle Charge) '
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