NUCLEAR energy supplies 20 percent of the electricity
used in the U.S. and 16 percent of that used throughout the world. But as
the global use of nuclear energy grows, so do concerns about the vulnerability
of nuclear plants and fuel materials to misuse or attacks by terrorists.
A Livermore team is part of a Department of Energy (DOE) collaboration that
is addressing both the growing need for nuclear energy and the concern over
nuclear proliferation by pursuing a concept called SSTAR, a small, sealed,
transportable, autonomous reactor.
SSTAR is designed to be a self-contained reactor in a tamper-resistant
container. The goal is to provide reliable and cost-effective electricity,
heat, and freshwater. The design could also be adapted to produce hydrogen
for use as an alternative fuel for passenger cars.
Most commercial nuclear reactors are large light-water reactors
(LWRs) designed to generate 1,000 megawatts electric (MWe) or more. Significant
capital investments are required to build these reactors and manage the
nuclear fuel cycle. Many developing countries do not need such large increments
of electricity. They also do not have the large-scale energy infrastructure
required to install conventional nuclear power plants or personnel trained
to operate them. These countries could benefit from smaller energy systems,
such as SSTAR, that use automated controls, require less maintenance work,
and provide reliable power for as long as 30 years before needing refueling
Many of the countries in need of nuclear energy are among the 187
nations that have signed the Non-Proliferation Treaty (NPT) enacted in 1970.
Under the terms of this treaty, the five acknowledged nuclear-weapon states—the
U.S., Russian Federation, United Kingdom, France, and China—agreed
not to transfer nuclear weapons, other nuclear explosive devices, or related
technology to those signatory states that have no nuclear weapons. These
nonnuclear states agreed not to acquire or produce nuclear weapons or nuclear
explosive devices, and in exchange, they have access to peaceful nuclear
technology developed by the five nuclear signatories. Unfortunately, the
NPT has some weaknesses, as demonstrated by the recent disagreements with
Iran and North Korea. Although both countries had signed the NPT, their
nuclear energy programs are not in keeping with their treaty agreements.
To address this problem, DOE is funding an initiative to develop
a conceptual design of a reactor that will deliver nuclear energy
to developing countries and significantly reduce the proliferation concern
associated with expanded use of nuclear power. Three national laboratories
are collaborating on this initiative. Lawrence Livermore, which leads the
collaboration, is researching materials and coolants for the reactor and
evaluating how it can be deployed. Argonne is designing the reactor, and
Los Alamos is contributing its expertise on coolant and fuel technologies.
The SSTAR design will accomplish DOE’s goals by allowing the U.S.
to provide a tamper-resistant reactor to a nonnuclear state while still
safeguarding the nation’s sensitive nuclear technology. SSTAR will
also secure the nuclear fuel because, after its operation, the sealed reactor
will be returned to a secure recycling facility for refueling or maintenance.
Designed to be deployable anywhere in the world, SSTAR may also
meet a national need. In the U.S., the Nuclear Regulatory Commission (NRC)
oversees more than 100 nuclear power plants that were built during the 1960s
and 1970s. SSTAR would provide a secure and cost-effective system to replace
older nuclear reactors as well as aging fossil-fuel plants, particularly
in an isolated location.
Lawrence Livermore, Los Alamos, and Argonne
national laboratories are designing a self-contained nuclear
reactor with tamper-resistant features. Called SSTAR (small,
sealed, transportable, autonomous reactor), this next-generation
reactor will produce 10 to 100 megawatts electric and
can be safely transported on ship or by a heavy-haul transport
truck. In this schematic of one conceptual design being considered,
the reactor is enclosed in a transportation cask.
One Size Fitting Many Needs
SSTAR is designed
as a lead-cooled fast reactor (LFR) that can supply 10 to 100 MWe with a reactor system that can be transported
in a shipping cask. Fast reactors typically use liquid metal coolants, such
as lead, lead–bismuth, or sodium, instead of water. Neutron kinetic
energy is about 250 kiloelectronvolts in LFRs—much greater than
in LWRs, where the low mass of hydrogen in the water coolant slows neutron
velocity and, thus, energy to about 0.025 to 0.05 electronvolt. With
fast-moving neutrons, SSTAR could produce the fissile material it needs
to fuel continued operation at the same time that it generates energy. Spent
fuel in the form of uranium and plutonium would remain in the reactor to
generate power for up to 30 years. The spent reactor would then be returned
to a secure recycling facility to close the fuel cycle and to minimize the
high-level wastes generated by nuclear reactors, thus reducing the space
and infrastructure needed for the long-term storage of radioactive wastes.
The concept for recycling is to have almost all of the waste burned in the
project leader Craig Smith, a nuclear engineer in Livermore’s Energy and Environment Directorate, the reactor will be
about 15 meters tall by 3 meters wide and will not weigh more
than 500 tons—small and lightweight enough to be transported on a
ship and by a heavy-haul transport truck. “With SSTAR, countries won’t
need a large nuclear reactor industry to benefit from nuclear energy,” says
Smith. “Because the supplier nation will provide both the reactor
and the associated fuel-cycle services, the host nation can produce electricity
without needing an independent supply of uranium or other fuel at the front
end of the cycle. The host nation also won’t have to dispose of the
nuclear waste at the back end of the cycle.”
the current SSTAR design reduces the potential for a terrorist to divert
or misuse the nuclear materials and technology. Nuclear
fuel will be contained within the sealed, tamper-resistant reactor
vessel when it is shipped to its destination, and the spent reactor core
returned to the supplier for recycling.
proliferation concerns with other features as well. No refueling is necessary
during the reactor’s operation, which eliminates
access to and long-term storage of nuclear materials on-site. The design
also includes detection and signaling systems to identify actions that threaten
the security of the reactor. And because of the reactor’s small size
and its thermal and nuclear characteristics, the design can include a passive
method to shut down and cool the reactor in response to hardware or control
When it is upright, SSTAR will be about
15 meters high and 3 meters wide, and its total weight
will not exceed 500 tons. This compact size will allow the
nuclear reactor to be transported on a ship and by a heavy-haul
Reduced Operating Costs
offers potential cost reductions over conventional nuclear reactors.
Using lead or lead–bismuth as a cooling material instead
of water eliminates the large, high-pressure vessels and piping needed to
contain the reactor coolant. The low pressure of the lead coolant also allows
for a more compact reactor because the steam generator can be incorporated
into the reactor vessel. Plus with no refueling downtime and no spent fuel
rods to be managed, the reactor can produce energy continuously and with
SSTAR may also
reduce costs for the transportation industry by providing a cheaper
source of fuel to power passenger cars. Because LFRs
can potentially operate at high temperatures (up to about 800°C), the
reactor can be used to generate the heat required for efficient
production of hydrogen, which is the preferred fuel for fuel-cell
vehicles and hybrid
vehicles burning hydrogen in an internal combustion engine. (See
June 2003, Flexibly
Fueled Storage Tank Brings Hydrogen-Powered Cars Closer to Reality.)
As oil production becomes more expensive and constraints on carbon
dioxide emissions tighten, the search
for alternatives to fossil fuels becomes more important. SSTAR
has the potential to address a critical national
and international need for the future.
Tackling the Design Challenges
must be addressed before the SSTAR design is ready for prototype
testing. The Livermore team must develop materials for
the fuel and coolant boundary that are compatible with the coolant.
Lead, especially when alloyed with bismuth, tends to corrode the
fuel cladding and structural steel. Controlling the oxygen in the coolant
corrosion. In addition, the team must identify materials that would
best withstand the damaging effects of long-term exposure to fast
damage could include material swelling and ductility loss, both
of which may limit the life of the reactor.
In 2003, the
Laboratory’s SSTAR team participated in a feasibility
study with a team from the Central Research Institute for Electric Power
Industry (CRIEPI) in Japan. In this study, the two teams evaluated a modified
design, developed by the Japanese team, for a small liquid metal–cooled
reactor using sodium as a coolant. A scientist from CRIEPI is now working
at Livermore, and the teams are sharing the results from their respective
features also will be developed to ensure that any failure in the
control system will shut down the reactor and initiate a
natural convection system to cool the reactor core and reactor
vessel. The characteristics of these features will depend on the
geometry and mechanical
support system provided for the nuclear reactor. In addition, the
prototype will test the performance of the passive safety features
and the system
designed to monitor them.
spent reactor will be radioactive, the research team must develop
packaging and transportation systems so the reactor can be
removed safely. The team also must design a process to cool the
reactor while it is being shipped to the recycling facility. The
for meeting these challenges may affect the maximum power level
that can be achieved.
NRC plans to
certify the SSTAR design using a new license-by-test approach,
rather than the license-by-design approach that it used to certify
most of the existing commercial nuclear power plants. NRC’s license-by-test
process is similar to the certification process used by the U.S. Federal
Aviation Administration for commercial airliners. To be certified, the SSTAR
prototype must demonstrate in a test environment that it can safely withstand
accidents, including the most improbable ones such as failure of the active
shutdown and shutdown heat-removal systems.
But the tri-laboratory
collaboration has more work to do before an SSTAR demonstration.
According to Smith, the team plans to refine the
SSTAR design and then develop a prototype reactor, which could
be ready for testing as early as 2015. The Livermore team feels
confident that SSTAR
will provide a new-generation reactor—one that is safe, proliferation-resistant,
and able to operate anywhere in the world.
Key Words: Central Research Institute for Electric Power Industry
(CRIEPI); lead-cooled fast reactor (LFR); Non-Proliferation Treaty
(NPT); nuclear reactor; small, sealed, transportable, autonomous
For further information contact Craig Smith
(925) 423-1772 (email@example.com).
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