POWER August 2011 - 71

NUCLEAR powER
tration made the CRBR project a funding
priority in fiscal year 1982 and said it
" should be constructed in a timely and
expeditious manner. " However, on Oct.
26, 1983, the U.S. Senate terminated
funding for the project.
Fast Flux Test Facility (FFTF, 1978-
1993, 1997-2001). Construction of the
400-MWth FFTF in Hanford, Wash., was
completed in 1978; initial operation followed
in 1980. From April 1982 to April
1992, it operated as a national research
facility to test various aspects of commercial
reactor design and operation, especially
relating to breeder reactors. The
FFTF is not a breeder reactor itself, but
rather a sodium-cooled fast neutron reactor.
By December 1993, the number of
uses for the reactor was diminishing, so
the decision was made to deactivate it.
In January 1997, the DOE ordered that
the reactor be maintained in a standby
condition, pending a decision to incorporate
it into the U.S. Government's tritium
production program for both medical and
fusion research. In December 2001, deactivation
continued after it was determined
that the FFTF was not needed for
tritium production. In May 2005, the core
support basket was drilled to drain the remaining
sodium coolant, effectively making
the reactor unusable. In April 2006,
the FFTF was honored by the American
Nuclear Society as a National Nuclear Historic
Landmark.
Recent Advanced Reactor and Nuclear
Fuel Cycle Programs (1999-Present).
The U.S. slowly restarted its advanced
reactor and nuclear fuel cycle programs
via the Generation IV Nuclear Energy
Systems program, the Generation IV International
Forum, Advanced Fuel Cycle
Initiative, and the Global Nuclear Energy
Partnership (GNEP). (See " Developing the
Next Generation of Reactors, " April 2008
in the POWER archives at www.powermag
.com.) In April 2009, the DOE announced
the cancellation of the U.S. domestic
component of GNEP, and in June 2009
it announced that it is no longer pursuing
domestic commercial reprocessing of
nuclear fuel. The program is now referred
to as the International Framework for
Nuclear Energy Cooperation.
August 2011 | POWER
cancelation of the ALMR/IFR program, GE
Hitachi Nuclear Energy (GEH) continued
to develop the next-generation 330-MWe SPRISM
reactor (Figure 1, p. 68).
In all three designs, the technologies that
make PRISM unique remained constant: passive
reactor core cooling and residual heat
removal systems, metallic fuel, and electromagnetic
pumps (EMPs). An EMP is designed
to move liquid metal or any electrically conductive
liquid magnetic material, such as molten
salt coolant, using electromagnetic force without
a mechanical motor-pump connection.
Remarkable Reactor Design
Nuclear reactors operate on two types of neutrons,
based on their energy levels: low-energy
(thermal) or high-energy neutrons. In a traditional
LWR containing uranium-235 (U-235)
as the main component in nuclear fuel, thermal
neutrons are used to sustain a fission chain reaction.
In order to increase the number of thermal
neutrons, hydrogenous materials (such as
water) are used to slow down the high-energy
neutrons and turn them into thermal neutrons.
The thermal neutrons can then be absorbed by
U-235, which undergoes further reactions to
produce even more neutrons in order to sustain
a fission chain reaction.
Reactors, such as the PRISM, utilize the
high-energy neutrons for a sustained fission
chain reaction. Because PRISM uses liquid
sodium as a coolant instead of water, the
high-energy neutrons produced from fission
do not slow down when they come in contact
with the sodium coolant. Sodium becomes a
liquid at 208F and boils at 1,621F. Because
the PRISM reactor is designed to operate between
640F and 905F, the properties of sodium
make it an excellent coolant in a liquid
phase with a high heat transfer coefficient.
Additionally, the high-energy neutrons are
well suited for fissioning transuranics from
commercial LWRs (one of the waste streams)
and converting them into short-lived " fission
products. " This reaction produces heat energy,
which is converted into electrical energy.
It also eliminates the need to permanently
store the transuranic waste.
Fuel and Reactor Core. Most LWR fuel
rods are designed as 14-foot-long assemblies
containing uranium oxide. The 10-foot-long
metallic PRISM fuel bundles are constructed of
an HT9 ferritic alloy and contain a combination
of recycled uranium, plutonium, and zirconium.
The compact core design requires only 40 fuel
assemblies. The fuel is expected to stay in the reactor
for about six years, with one-third removed
every two years. The used PRISM fuel is then
recycled after removal of the fission products.
PRISM has a conversion ratio less than
one, which means that the reactor consumes
all the fissile material in the UNF, eliminating
production of weapons-grade materials.
Additional modifications to the core can be
made to use either a metal fuel or an oxidebased
fuel without changes to the reactor
structure or refueling system.
The PRISM core power rating ranges from
800 MWth to 1,000 MWth. The low-pressure
pool-type design with a containment vessel
surrounding the reactor vessel precludes
a large loss-of-coolant accident (LOCA).
Therefore, PRISM does not require an emergency
core cooling system similar to those in
current LWRs (Figure 3).
Intermediate Heat Transport System.
The internal EMPs circulate the molten so3.
Core contained. The liquid metal-cooled fast breeder reactor " pool " design is illustrated.
The heat exchanger loop is immersed in the reactor pool that contains nonradioactive
sodium, which is then piped to a different structure that transfers heat to a separate steam loop
to produce steam for a conventional steam turbine. Source: DOE
Cold plenum
Hot plenum
Control rods
Steam generator
Turbine Generator
Heat
exchanger
Condenser
Heat sink
Primary
sodium
(hot)
Pump
Pump
Core
Primary sodium (cold)
Pump
Secondary sodium
Electrical
power
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POWER August 2011

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