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It may also prove feasible to backfit existing pressurized water reactors with
spectral-shift control. Such backfitting might possibly be performed in some completed
plants where the layout favors modifications.
benefits of backfitting would have to be great to justify the cost of replacement power
during plant modification. A second and potentially more attractive alternative is the
possibility of modifying plants still in the early stage of construction for spectral-
shift control, or of incorporating features into these plants which would allow conversion to
spectral-shift control to be easily accomplished at a later date.
However, even when judged feasible, the
In order to establish the potential gains in resource utilization which might be
realized with spectral-shift control, scoping mass balance calculations have been performed
by Combustion Engineering for SSCRs operating on both the LEU cycle and on thorium-based
cycles, including the denatured 233U cycle.5 The calculations were performed for the C-E
system 80TM core and lattice design, with the intent of updating the earlier analyses re-
ported by Edlund to the reactor design and operating conditions of modern PWRs using state-
of-the-art analytic methods and cross sections. Preliminary results from this evaluation
are presented in Table 4.2-1.
Note that these results were obtained using the standard
System 80 design and operating procedures, and no attempt has been made to optimize either
the lattice design or mode of operation to fully take advantage of spectral-shift control.
For the LEU throwaway mode, Table 4.2-1 indicates a reduction of roughly 10% both
in ore requirements and in separative work requirements relative to the conventional PWR
(compare with Case A of Table 4.1-1).
the ore demand (and separative work) for the MEU/Th case by about 20% (compare with Case D
in Table 4.1-1).
If uranium recycle is allowed, the SSCR also reduces
Of particular interest to this study is the reduced equilibriim cycle makeup re-
quirements for the spectral-shift reactor fueled with 233U. As indicated, the equilibrium
cycle makeup requirement is 236 I. 233U/GWe-yr as opposed to 304 kg 233U/GWe-yr for the
conventional PWR (see Case E i n Table 4.1-1). The reduced 233U requirements, coupled with
the slightly higher fissile plutonium production, would allow a given complement of energy-
center breeder reactors to provide makeup fissile material for roughly 40% more dispersed
denatured SSCRs than conventional denatured PWRs. A comparison of the Pu/Th case with
Case H in Table 4.1-1 shows that the SSCR and PWR are comparable as transmuters. These
results are, of course, preliminary and are limited to the performance of otherwise un-
modified PWR systems, A more accurate assessment of SSCR performance, including the
performance of systems optimized for spectral-shift control, will be performed as part of
the NASAP program.6
The preliminary studies performed to date and the demonstration of spectral-
shift control in the Vulcain core have served to demonstrate the feasibility of the
concept and to identify the resource utilization and economic incentives for this
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