ORNL-5388 - the Molten Salt Energy Technologies Web Site

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Energ-y-Center-Constrained Fuels
E.
4-9
F. P u - ~ ~ mixed-oxide ~ T ~ fuel. Notation: Pu02/Th02; (Pu-Th)O,;.Pu/Th.
G.
LEU fuel with plutonium recycle.
P U - ~ ~ mixed-oxide U
fuel, as proposed for currently designed LMFBRs. Notation:
Pu02/UO,; Pupa u; PU/U.
Reference Fuels
H. Highly enriched 235U fuel (containing approximately 93% 235U) mixed with thorium
I.
fertile material, as currently used in HTGRs. Notation: HEU(235)/Th; US(HE)/Th.
Highly enriched 233U fuel (containing approximately 90% 233U) mixed with thorium
fertile material. Notation: HE(233)/Th; U3/Th; US(HE)/Th.
Including plutonium-fueled reactors within the energy centers serves a two-fold purpose:
It provides a means for disposing of the plutonium produced in the dispersed reactors, and
it provides for an exogeneous source of 233U.
The discussion of LWRs operating on these various fuel cycles presented in Section
4.1 is followed by similar treatments of the other reactors in Sections 4.2 - 4.6. The
first, the Spectral-Shift-Controlled Reactor (SSCR), is a modified PWR whose operation on
a LEU cycle has been under study by both the United States and Belgium for more than a
decade. The primary goal of the system is to improve fuel utilization through the inf
creased production and in-situ consumption of fissile plutonium (Pu ). The capture of neu-
trons in the 238U included in the fuel elements is increased by mixing heavy water with
the light-water moderator-coolant, thereby shifting the neutron spectrum within the core
to energies at which neutron absorption in 238~ is more likely to occur. The heavy water
content in the moderator is decreased during the cycle as fuel reactivity is depleted.
increased capture is also used as the reactor control mechanism. The SSCR is one of a class
of reactors that are increasingly being referred to as advanced converters, a term applied
to a thermal reactor whose design has been modified to increase its production of fissile
material.
Heavy-water-modi fied thermal reactors are represented here by Canada's naturaluranium-fueled
CANDUs. Like the SSCR, the CANDU has been under study in the U.S. as an
advanced converter, and scoping calculations have been performed for several fuel cycles,
including a slightly enriched 235U cycle that is considered to be the reactor's reference
cycle for implementation in the United States.
The high-temperature gas-cooled thermal reactors considered are the U.S. HTGR and
the West German Pebble Bed Reactor (PBR), the PBR differing from the HTGR in that it
utilizes spherical fuel elements rather than prismatic fuel elements and employs on-line re-
fueling. For both reactors the reference cycle [HEU(233U)/Th] includes thorium, and shifting
The