ORNL-4191 - the Molten Salt Energy Technologies Web Site

Table 6.1. Useful Life of MSBR Graphite
Average Power
Density
(w/crn3!
Life
40 2.0 5. I
40 1.5 7.2
20 2.0 10.8
20 1.5 14.4
as well as on the total dose. The dose rate in the
DFR was approximately ten times greater than that
expected in the MSBR, and if there is a significant
dose-rate effect, the life of the graphite in an MSBR
might be rather longer than shown in Table 6.1.
Flux Flattening
0. L. Smith H. T. Kerr
Eecause the useful life of the graphite moderator
in the MSBR depends on the maximum value of the
damage flux rattier than on its average value in the
core, there is obviously an incentive to reduce the
maximum-to-average flux ratio as much as possible,
provided that this can be accomplished without se-
rious penalty to other aspects of the reactor per-
formance. In addition, there is an iilcentive to
make the temperature rise in parallel fuel passages
through the core as nearly uniform as possible, or
at least to minimize the maximum deviation of fuel
outlet temperature from the average value. Since
the damage flux (in effect, the total neutron flux
above 50 kev) is essentially proportional to the
fission density per unit of core volume, the first
incentive requires an attempt to flatten the power
density per unit core volume throughout the core,
that is, in both radia.1 and axial directions in a
cylindrical core. Since the fuel moves through the
core only in the axial direction, the second in-
centive requires an attempt to flatten, in the radial
direction, the power density per unit volume of
fuel. Both objectives can be accomplished by
maintaining a uniform volume fraction of fuel salt
throughout the core and by flattening the power
density distribution in both directions to the
greatest extent possible.
87
The general approach taken to flattening the
power distribution is the classical one of pro-
-,
viding a central core zone with I