MIT LMFBR blanket research project. Quarterly progress report, January 1, 1979--March 31, 1979 Page: 10 of 16
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Cross section generation methods have been described in
detail in the last progress report. Basically a 10 group cross
section set was generated from the 50 group LIB-IV cross section set
(2), based on the actual geometry through the 1-DX portion of
SPHINX (3). Figure 2 shows the R-Z layout of the upper half of
the core used in burnup calculations by the two-dimensional burnup
code 2DB '(4). There are 64 radial mesh-and 24 axial mesh points.
Axially the core, internal blanket and radial blanket:assemblies
are cut into three different zones; the axial blanket is cut
into two zones axially. In this way the R-Z layout is divided
into 78 burnup zones.
The fuel assemblies consist of 217 fuel pins having an
0.23 inch outside diameter. The internal blanket assemblies
consist of 127 pins of 0.346 inch outside diameter. For the
moderated external'blankets, depending on the level of moderation
desired, space will be left for zirconium hydride pins. Fig. 3
shows a preliminary design of a blanket with 28 moderator pins.
It is interesting to note that this type of design has been
proposed for heterogeneous cores which have internal blanket
rods as an'integral part of their fuel assemblies rather than
as separate assemblies (5).
2.4 Power Peaking
One of the points of concern in using moderator rods in
blanket assemblies is the power peaking problem. Since the
number of moderator pins per assembly.is a function of the level
of moderation desired, an assembly with very high moderation_
(worst case) was studied. In this assembly there are 49 moderator
rods, corresponding to 38 volume percent moderator content.
The peaking was analyzed for an assembly in the first row of
the radial blanket at the central plane of the core, where the
highest power density exists. The peaking occurs at the position
where the blanket rod is surrounded by the moderator pins. From
this analysis the peak-to-average midplane pin power ratio is
calculated to be 1.224,.which corresponds to a peak linear heat
generation rate of 14.85 KW/ft. The design limit for the peak
linear heat generation rate (3a, 15% overpower) is 20.0 KW/ft.
Thus it can be concluded that in the proposed moderated blankets
the peak rod is well below the specified design limit.
Another point of concern in using zirconium-hydride is the
radiation damage to the rods. Based on our calculations, and
comparison with the experimentally available data it is.concluded
that the fluence experienced by the zirconium hydride rods
over several cycles is below the level experimentally proved to
cause no significant damage.
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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/m1/10/: accessed May 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.