MIT LMFBR blanket research project. Quarterly progress report, January 1, 1979--March 31, 1979 Page: 5 of 16
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2. Advanced Blanket Investigations
Work continues on the use of substantial moderator additions
to the radial blanket, coupled with shuffling of internal
blanket elements into the external blankets (a breed/burn fuel
cycle). This would offer a number of potential benefits includ-
ing provision of a greater power bonus from the blanket, and
flattening of radial blanket power. In addition, if use of
thorium fuel is contemplated, this may further enhance the
attractive features of this concept.
The basic concept (as described in previous progress
reports) is to breed plutonium in depleted uranium fueled
internal blankets (or U-233 in thorium fueled internal blankets)
and then to move the internal blanket assemblies into the radial
blanket and there to burn the fissile isotopes to the maximum
extent practicable. This strategy should lower the steady state
core enrichment required: the critical fissile Pu enrichment
of an infinitely large (no leakage) fast reactor core is around
8.5%. The critical enrichment of a large ( '1000 MWe) but
finite homogeneous fast reactor core is around 15% (and for a
heterogeneous core around 19%). The difference in the critical
enrichment.of an infite (no leakage) system with a realistic
core is basically due to the large leakage of core neutrons to
the radial and axial blankets. In a conventional fast reactor
the 25 to 30% of the core neutrons that leak to the blankets
are used to breed plutonium.. If the leakage to the radial
blanket can be substantially reduced, then the steady-state core
enrichment can be reduced to values closer to those for an
infinite homogeneous system. One way of doing this is to replace
the radial blanket with a system that does not act like a neutron
sink: in particular, a critical or near-critical system. If
enough plutonium or U-233 can be bred in the internal blankets, in
a reasonable time, the internal blanket can be moved to the
radial blanket to create a critical system. This shuffling scheme
has the added advantage of deferring or eliminating the reproces-
sing requirement for the internal or radial blankets.
The rate of buildup of plutonium in the internal blankets
varies radially and axially; on the average, close to 2%
plutonium can be built in annually for each of the first two
years, but the rate of build up falls off thereafter as the satura-
tion limit of plutonium is approached. Based on this observation,
a critical plutonium radial blanket (which requires approximately
8.5% fissile plutonium) cannot be achieved in a reasonable time
span. We have evaluated what can be achieved, however, to
determine whether the benefits are still worthwhile.
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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/m1/5/: accessed May 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.