MIT LMFBR blanket research project. Quarterly progress report, January 1, 1979--March 31, 1979 Page: 7 of 16
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Unlike the.U-Pu system, however, an epithermal Th-U233
system (moderated by zirconium hydride, for example) requires
only 3.5% to 4% U23 to go critical. Thus it might be possible
to breed enough fuel in the internal blanket to feed a critical
external blanket. This system is currently under study.
2.2 Fissile. Build-up in Internal Blankets
Since the rate of plutonium or U-233 buildup in the internal
blanket is an important parameter in the present work, a separate
study was performed on.ways to enhance the rate of fissile
Originally there were indications that softening of the
spectrum in internal blankets would increase the rate of
fissile build up. This thought was reinforced by the fact that
the ratio, c28
.which is directly related to fissile buildup peaks around 10 Key.
The results of the study showed that spectrum softening does not
help the rate of fissile buildup, but actually degrades the
rate of buildup. The basic explanation for this result in the
light of the above argument is that selective softening of
the spectrum to-create a peak around 10 Key is not possible:
softening occurs over a broader -range, and the net effect is
detrimental. It was concluded that the highest rate of fissile
buildup can be achieved in the hardest blanket spectrum.
Based on this conclusion uranium or thorium metal are the most
desirable materials for the internal blankets as far as fissile
buildup is concerned. These materials will be considered further
in the study of internal blanket designs.
2.3 Reference Cores
The planar view of the core used in concept evaluation is
shown in Fig. 1. The core consists of 780 fuel assemblies and 415
internal blanket assemblies. The number of rows of radial
blanket assemblies depends on the amount of moderator rods-
desired. For example, there are 414 assemblies in a three-row
radial blanket. This number is equal to the number of internal
blanket; elements. Thus with no extra-assembly moderation all
internal blankets can be moved to radial blankets n a three row
configuration. Four rows of radial blanket equals 564 assemblies,
and this allows for 27% extra-assembly moderator by volume. Higher
moderator content is possible if the number of radial blanket
positions is increased. Although both ex-assembly and in-assembly
moderation is being considered, the latter concept is currently
favored. Beyond the radial blanket there are three rows of
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Driscoll, M.J. MIT LMFBR blanket research project. Quarterly progress report, January 1, 1979--March 31, 1979, report, April 20, 1979; Cambridge, Massachusetts. (https://digital.library.unt.edu/ark:/67531/metadc1109556/m1/7/: accessed May 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.