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Will “Smaller and Smarter” replace “Bigger and Bulkier”?
Presently, around the world there are 435 nuclear reactors operating generating roughly 374
GWe of electrical power (World Nuclear Association, 2013). Most of these reactors are large
(>1000 MWe) and require a substantial infrastructure to support them (Earp, 2013). Small
Modular Reactors (SMRs), which are about one-third (<300MWe) of the size of existing nuclear
power plants, are currently being pursued. So, will “Smaller and Smarter” replace “Bigger and
Bulkier”?
The growing concern about global warming and climate change has instilled a sense of urgency
to develop and deploy electricity-generating technologies that do not emit CO2 or other
greenhouse gases (GHGs). SMRs can be manufactured in U.S. factories and then be transported
to construction sites that include remote locations or military bases where large reactors are not
practical. SMRs offer the advantage of lower initial capital investment, scalability and siting
flexibility at locations unable to accommodate conventional larger reactors. SMRs could be used
by smaller utilities, by smaller countries with financial or infrastructural constraints, in isolated
regions or for distributed power needs, and for various non-electrical applications (process heat,
desalination, oil recovery for tar sands and oil shale, and district heating). SMRs can be coupled
with other energy sources, including renewable (such as, wind, biomass, geothermal, hydro and
solar) and fossil energy. Retrofitting of aging conventional power plants with SMRs is an option
that would leverage the existing siting and electrical grid transmission system (Halfinger and
Haggerty, 2012).
The modular approach enables a "plug and play" implementation that requires minimal on-site
preparation (U.S. DOE, SMR Fact Sheet). "You can put them together like Legos on a job site,"
says Christopher Mowry of B&W (USA Today, 2012). Additional modules can be incorporated
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incrementally as the demand for energy increases and financing becomes available. According to
Peter Lyons, Assistant Secretary for Nuclear Energy at DOE, costs for an SMR plant are $4700
to $6000 per KWe or about $900 to $1200 million for a 200 MWe plant. For SMRs to be an
economically viable alternative to standard GWe scale reactors, they must be deployed in large
numbers (Glaser et al., 2013). Orders of several plants per year would be required before an
automated factory for building these plants could be justified (ANS Nuclear Café, 2013).
Although some of the technology has been used for naval propulsion applications, these systems
have not yet been commercialized in the U.S. The components of the SMRs will be “Made in the
U.S.A.,” which will create new jobs and increase exports. But, there is competition from other
countries racing to design, build and market an offering of SMRs. The World Nuclear
Organization reports that worldwide there are currently two SMRs operating, three SMRs under
construction, 12 different small reactors with technology sufficiently advanced for near-term
deployment, and another eight reactors in the same capacity range are listed as being in earlier
stages of design. These reactors all have a generating capacity of at least 25 MWe. Countries
with SMRs under design or already designed include Pakistan, India, Russia, Argentina, China,
South Korea, South Africa, Japan and the U.S. (World Nuclear Organization, 2013). Examples
of foreign advanced SMR designs include the 100 MWe integral pressurized water reactor
(iPWR) South Korean System-Integrated Modular Advanced Reactor (SMART) and China’s
twin 210 MWe HTR-PM gas-cooled reactors.
Potential sales of SMRs to foreign nations could be lucrative for the U.S., especially if fuel sales
contracts are established. If the spent fuel is returned to the U.S., it would help alleviate
worldwide proliferation concerns. However, due to the higher fissile content in the spent fuel
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they generate, SMRs could present increased proliferation risks unless offset by specific
safeguards or design features (Glaser et al., 2013).
Key benefits of SMR technology are reliance upon passive safety systems, use of natural
circulation for emergency feedwater cooling, and elimination of the need for external emergency
power. SMRs offer increased safety by eliminating major accident initiators (for example, large
pipes in primary circuit), by improving decay heat removal and including more efficient passive
heat removal from the reactor vessel, and use of seismic isolators for increased earthquake safety
(Vujic et al., 2012). SMR vendors purport that the potential consequences of an accident relative
to that of a large plant are reduced due to the small size of the reactor and the low power density
limits. It can be argued that these reactors are safer than traditional nuclear power plants since
they include a containment vessel surrounded by concrete and are located underground.
While the development of new reactor concepts offers the potential for revolutionary
improvements to reactor performance and safety, it is necessary to demonstrate that engineered
safety features provide an acceptable level of protection to workers and the public. Critics of
SMRs point to the possibility of a new set of problems associated with these reactors. Reducing
the size of the unit results in a loss of economy of scale and operating more units increases the
chances of a safety incident occurring at one of them. As with any new design, the full details
will only be understood once an SMR is built and operated for some period of time.
The successful licensing and widespread deployment of SMRs hinges to a large extent on siting
considerations. The U.S. Department of Energy (DOE) Office of Nuclear Energy’s Small
Modular Reactor Licensing Technical Support program is working to advance the licensing and
commercialization of domestic SMR designs that are relatively mature and can be deployed in
the next decade. The NRC is engaged in pre-application discussions with vendors advocating
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SMR designs based upon three different technologies – light water reactors, high-temperature
gas reactors and liquid metal-cooled reactors (Trikouros, 2012). SMRs that are designed to use
light water reactor technology are considered by the nuclear community to be the most promising
candidates for near-term SMR deployment since they have the most mature designs and are
currently involved in pre-application interactions with the Nuclear Regulatory Commission
(NRC) (NEI Position Paper, 2012). There are currently four iPWR designs currently being
developed by U.S. industry (Holtec, mPower, NuScale and Westinghouse).
Department of Energy Sponsored SMR Development
To develop a new generation of domestically-produced nuclear power, the Obama administration
announced on November 20, 2012 that it will fund up to half the cost of a five-year project to
design and commercialize SMRs in the United States. The Department of Energy (DOE) is
supporting the development and deployment of SMRs through two public-private partnerships:
1. Former Secretary of Energy Dr. Steven Chu stated when announcing the first award,
“Low-carbon nuclear energy has an important role to play in America's energy future."
President Obama's thrust is for an energy strategy that reduces GHG emissions and
provides affordable energy. The first round of DOE funding was awarded to the mPower
America project team consisting of B&W, Bechtel and the Tennessee Valley Authority
(TVA). In April 2013, an agreement was signed providing B&W with $79 million in
federal funding for commercialization of the mPower design. The team has set milestones
of submitting the design certification application to the NRC in 2014. TVA may also
submit a combined construction and operating license application to the NRC in 2015 for
two SMRs to be built at the Clinch River site in Oak Ridge, Tennessee.
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2. NuScale Power, LLC was selected on December 12, 2013 as the winner of the second
round of the U.S. DOE’s competitively-bid, cost-sharing program to develop nuclear
SMR technology. In announcing the second award, Energy Secretary Moniz said, “Small
modular reactors represent a new generation of safe, reliable, low-carbon nuclear energy
technology and provide a strong opportunity for America to lead this emerging global
industry.” As part of the award, NuScale will receive up to $225M in federal funding
over a five-year period to support the accelerated development of its 45 MWe NuScale
Power Module™ SMR technology. The design features natural circulation, coolant flow
residual heat removal and emergency core cooling systems powered by natural forces and
a common pool that provides seismic dampening and radiation shielding. During extreme
events, such as those that occurred at the Fukushima nuclear plant, 30 days of core and
containment cooling are provided without the addition of water (Reyes, 2013).
These public-private partnerships represent a significant investment in first-of-a-kind
engineering, design certification and licensing for SMRs. DOE’s goal is to have these reactors
operational in the early 2020’s.
Description of mPower Design
The focus of this essay is on the Generation mPower design. The origins of mPower reactor can
be traced to the nuclear-powered merchant ship, the Otto Hahn, from the B&W maritime reactor
program (Halfinger and Haggerty, 2012). The reactor aboard the Otto Hahn had an integral
steam generator, located above the core, which provided superheated steam to drive turbines for
power.
The mPower reactor is an iPWR design in which the primary coolant system and all components
(i.e., pressurizer, steam generators, and reactor coolant pumps) are enclosed within a single
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pressure vessel (shown in Figure 1). As a result, the coolant remains within the vessel, except for
an instrumentation tap, pressurizer spray line, and small penetrations located above the core for
letdown, purification and makeup. Decay heat removal, reactor vessel depressurization, lowpressure coolant injection and reactor cavity flooding are provided by passive safety systems.
Large seismically qualified tanks are available to supply cooling water for at least seven days.
Each Generation mPower reactor is designed to provide 180 MWe, in contrast to about 1,000
MWe for a typical large reactor, and is envisioned to operate in pairs sharing a common turbinegenerator unit. To enhance safety and security, these light-water-cooled SMRs have separate,
independent underground containments and safety systems for each reactor (Figure 2). The
containment building and spent fuel pool facility are seismic category I flood-resistant structures
located below grade level. In the event of an accident, radioactive material is confined by the
containment building and passive hydrogen recombiners prevent the buildup of explosive
hydrogen. The passive safety systems work without AC power or operator action for a period of
72 hours to protect the core, provide cooling and prevent the release of radioactive materials to
the environment.
The mPower reactor will operate on a 48-month cycle, after which the core will be completely
changed out. The fuel consists of shortened versions of standard 17 x 17 commercial uranium
oxide (<5.0wt% 235U) fuel assemblies. An extensive testing program to verify specific
component design features and assess integrated system performance is being conducted. The
Integrated System Test facility in Bedford County, Virginia is a scaled prototype of the mPower
reactor used to confirm integral system design, demonstrate passive engineered safety systems
and plant control systems, develop emergency procedures, train operators, confirm the design
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verification methodology, and document reactor performance over a full spectrum of normal and
transient operating conditions (Martin et al., 2013).
Figure 1. The B&W mPower SMR integrates the Figure 2. Underground containment
nuclear core and steam generators in a single vessel structure housing two B&W mPower SMR
(source: greencarcongress.com).
modules (source: generationmpower.com).
INL’s Role in Advancing SMR Technology
The Idaho National Laboratory (INL) is advancing the development of nuclear reactor
technology in several key areas (Grossenbacher, 2013). INL has a strong capability in the
computational modeling of fuels and reactor performance. This includes the development of the
Multiphysics Object-Oriented Simulation Environment (MOOSE) “herd” of computer codes
(e.g., BISON, MARMOT, FOX, ELK, etc.), as well as the new Reactor Excursion and Leak
Analysis (RELAP)7 and the legacy RELAP5-3D systems code. Development and testing of new
fuels and materials is performed through partnerships with industry and universities at the
Advanced Test Reactor National Scientific User Facility (NSUF). Facilities and equipment for
examining unirradiated and irradiated fuels and materials is available at the Center for Advanced
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Energy Studies and the Materials and Fuels Complex. Design certification and licensing
activities are supported by the SMR Licensing Technical Support Program. The INL sponsors
student internships to train the future nuclear workforce.
Conclusion
This is an exciting time to be entering or working in the nuclear field. Several design
certification applications for new reactors, including the Advanced Boiling Water Reactor
(ABWR), Advanced Passive 1000 (AP1000), Economic Simplified Boiling Water Reactor
(ESBWR), U.S. EPR and U.S.-Advanced Pressurized Water Reactor (APWR) have been
submitted to the U.S. NRC. Worldwide, over 70 new nuclear reactors are under construction
(World Nuclear Association, 2013). In the U.S., four new Westinghouse AP1000 reactors are
being built at the Vogtle site in Georgia by Southern Co.
So, will today’s “Smaller and Smarter” modular reactors replace the “Bigger and Bulkier”
mindset of yesterday? There are applications for which SMRs are ideally suited, but it is not
likely that they will completely replace large gigawatt-scale reactors. Rather, they will be another
option to incorporate into the current energy mix that includes coal, natural gas and renewables. I
am optimistic that construction of multiple SMRs in the U.S. is on the horizon. It would be
exciting if an SMR was constructed at the INL site. Perhaps this would be a liquid-metal cooled,
fast reactor to provide a domestic capability for testing advanced fuels and materials. This could
be part of the NSUF Program, providing opportunities for students (like me!) to contribute to the
next generation of nuclear technology. I am planning to go to college at Penn State. During a
private tour, I was able to see the Breazeale Nuclear Reactor, a one MWt Training, Research,
Isotopes, General Atomic reactor. The nuclear future looks bright and I am eager to be a part of
it!
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References
ANS Nuclear Café, Small Modular Reactors at ANS 2013 Winter
www.ansnuclearcafe.orf/category/small-modular-reactors, accessed 11/28/13.
Meeting,
Earp, J.E., Briefing: Small Modular Reactors, Proceedings of the ICE – Energy, Vol. 166, Issue
2, April 2013, p. 53-57.
Glaser, A., et al., Resource Requirements and Proliferation Risks Associated with Small Modular
Reactors, Nuclear Technology, Vol. 184, Number 1, October 2013, p. 121-129.
Grossenbacher, J., A Perspective on the Challenge Facing SMRs, presented at From Concept to
Reality: Small Modular Reactors, Realizing the Potential of SMRs in the U.S. for the Future of
Nuclear Power, Idaho Falls, Idaho, October 20 – November 1, 2013.
Halfinger, J.A., and Haggerty, M.D., The B&W mPower Scalable, Practical Nuclear Reactor
Design, Nuclear Technology, Vol. 178, Number 2, May 2012, p. 164-169.
Martin, R.P., et al., Thermal-Hydraulic Design for the B&W mPower SMR, Nuclear
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Nuclear Energy Institute, Position Paper, Small Modular Reactor Source Terms, December 27,
2012.
Reyes, J.N., NuScale Plant Safety in Response to Extreme Events, Nuclear Technology, Volume
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Trikouros, N.G., A Perspective on Small Reactor Licensing and Implementation, Nuclear
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