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to the denatured cycle would consist initially in replacing the 93% 235U in 238U with 15
to 20% 235U in 238U. The HTGR has reached the prototype stage at the Fort Vrain plant in
Colorado and a PBR-type reactor has been generating electricity in West Germany since 1967.
While the above thermal reactors show promise as power-producing advanced converters,
they will not be self-sufficient on any of the proposed alternate fuel cycles and will re-
quire an exogenous source of 233U. An early but limited quantity of 233U could be provided
by introducing thorium within the cores of 235U-fueled LWRs, but, as has already been pointed
out in this report, for the long-term, reactors dedicated to 233U production will be required.
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In the envisioned scenarios those reactors primarily will be fueled with Pu . In the
calculations presented here a principal 23 % production reactor is the mixed-oxide-fueled
LMFBR containing thorium in its blanket.
blanket assemblies intermixed with fuel assemblies are examined. The possible advantages
and disadvantages of using metal- or carbide-based LMFBR fuel assemblies are also discussed.
Finally, some preliminary calculations for a helium-cooled fast breeder reactor (GCFBR) are
presented.
In addition, "advanced LMFBRs" that have
The consideration of fast reactors that burn one fissile material to produce another
has introduced considerable confusion in reactor terminology which, unfortunately, has not
been resolved in this report. In the past, the term fast breeder has been applied to a
fast reactor that breeds enough of its own fuel to sustain itself. Thus, the fast reactors
that burn 239Pu to produce 233U are not "breeders" in the traditional sense.
however, producing fuel at a rate in excess of consumption, which is to be contrasted with
the advanced thermal converters whose primary function is to stretch but not increase the
fuel supply.
transmuters was coined at ORNL.
any reactor that burns one fuel and produces another.
that the words fast and breeder are used synonymously. Thus in this report and elsewhere
we find various combinations of terms, such as LMFBR transmuter and converter transmuter.
The situation becomes even more complicated when the fast reactor design uses both 238U
and 232Th i n the blanket, so that in effect it takes on the characteristics of both a
transmuter and a breeder.
They are,
In order to distinguish the P u - ~ o - ~ ~ fast ~ U reactors from others, the term
Immediately, however, the word began to be applied to
Moreover, it soon became obvious
Finally, the reader is cautioned not to infer that only those reactors discussed in
this chapter dre candidates for the enerTy-center, dispersed-reactor scenarios. In fact,
the scenarios discussed in Chapter 6 do not even use all these reactors and they could
easily consider other reactor types.
assessment of the denatured 233U fuel cycle was based primarily on the availability of
data at the time the study was initiated (December, 1977).
The selection of reactors for this preliminary
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