Advanced Nuclear Reactors: Technology Overview and Current Issues
Congressional research reportFeb 17, 2023
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Advanced Nuclear Reactors: Technology
Overview and Current Issues
Updated February 17, 2023
Congressional Research Service
https://crsreports.congress.gov
R45706
SUMMARY
Advanced Nuclear Reactors: Technology
Overview and Current Issues
R45706
February 17, 2023
Mark Holt
All nuclear power in the United States is generated by light water reactors (LWRs), which were
Specialist in Energy Policy
commercialized in the 1950s and early 1960s and are now used throughout most of the world.
LWRs are cooled by ordinary (“light”) water, which also slows (“moderates”) the neutrons that
maintain the nuclear fission chain reaction. High construction costs of large conventional LWRs,
concerns about safety raised by the 2011 Fukushima nuclear disaster in Japan, growing volumes
of nuclear waste, and other issues have led to increased interest in unconventional, or “advanced,” nuclear technologies that
proponents say could be less expensive, safer, and more fuel efficient than existing LWRs.
The Energy Act of 2020 (Division Z of P.L. 116-260) defines an “advanced nuclear reactor” as a fission reactor “with
significant improvements compared to reactors operating on the date of enactment” or a reactor using nuclear fusion. Such
reactors include LWR designs that are far smaller than existing reactors, as well as concepts that would use different
moderators, coolants, and types of fuel. Many of these advanced designs are considered to be small modular reactors (SMRs),
defined by the International Atomic Energy Agency (IAEA) as reactors with electric generating capacity of 300 megawatts
(MW) and below. IAEA classifies reactors with 10 megawatts or less as microreactors.
Advanced reactors are often referred to as “Generation IV” nuclear technologies, with existing commercial reactors
constituting “Generation III” or, for the most recently constructed reactors, “Generation III+.” Major categories of advanced
reactors include advanced water-cooled reactors, which would make safety, efficiency, and other improvements over existing
commercial reactors; gas-cooled reactors, which could use graphite as a neutron moderator or have no moderator; liquidmetal-cooled reactors, which would be cooled by liquid sodium or other metals and have no moderator; molten salt reactors,
which would use liquid fuel; and fusion reactors, which would release energy through the combination of light atomic nuclei
rather than the splitting (fission) of heavy nuclei such as uranium. Most of these concepts have been studied, but relatively
few have advanced to commercial-scale demonstration, and such demonstrations in the United States took place decades ago.
To conduct new demonstrations of these technologies, Congress established the Advanced Reactor Demonstration Program
(ARDP) in FY2020, with an appropriation of $230 million (P.L. 116-94). In 2021, Congress, through the Infrastructure
Investment and Jobs Act (P.L. 117-58), appropriated $2.477 billion through FY2025, in addition to annual appropriations.
The Department of Energy (DOE) selected two demonstration projects for funding under ARDP in October 2020. Under the
awards, the two projects are to receive a total of $3.2 billion over seven years from DOE, with the project sponsors matching
that amount. Five potential future reactor demonstration projects received 80% cost-share awards under ARDP in December
2020, totaling $600 million of DOE funding over seven years. In addition to the ARDP projects, DOE announced a costshared award of up to $1.4 billion in October 2020 to demonstrate a water-cooled SMR at Idaho National Laboratory.
Tax credits for advanced nuclear reactors and other new zero-carbon power plants were included in the law commonly
referred to as the Inflation Reduction Act (IRA, P.L. 117-169). Qualifying plants can receive a 10-year electricity production
tax credit of up to 2.6 cents/kilowatt-hour (adjusted for inflation) or a 30% investment tax credit. IRA also includes $700
million for DOE to develop supplies of high-assay low enriched uranium (HALEU), needed for some reactor designs,
including the two non-LWR demonstration plants that DOE is supporting. HALEU, not currently available commercially, is
uranium enriched in the fissile isotope U-235 above the 3%-5% level used by existing commercial reactors but below the
20% threshold for highly enriched uranium. DOE’s HALEU program was authorized by the Energy Act of 2020.
Fundamental issues involving advanced reactors include the appropriate role of the federal government in developing and
deploying advanced nuclear power technologies and whether advanced nuclear power should be a major part of the nation’s
energy strategy. Major options for federal assistance include cost sharing, loan guarantees, power purchase agreements,
purchase of reactor capacity for research uses, and tax credits. Supporters of advanced nuclear technology contend that it will
be crucial in reducing emissions of greenhouse gases and bringing carbon-free power to the majority of the world that
currently has little access to electricity. However, some observers and interest groups have cast doubt on the potential safety,
affordability, and sustainability of advanced reactors. Because many of these technologies are in the conceptual or design
phases, the potential advantages of these systems have not yet been established on a commercial scale. Concern has also been
raised about the weapons-proliferation risks posed by the potential use of plutonium-based fuel by some advanced reactor
technologies.
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Contents
Introduction ..................................................................................................................................... 1
Advanced Reactor Technologies ..................................................................................................... 7
Advanced Water-Cooled Reactors ........................................................................................... 11
Small Modular Light Water Reactors ................................................................................ 11
Supercritical Water-Cooled Reactor.................................................................................. 12
Non-Water-Cooled Reactors ................................................................................................... 13
High Temperature Gas Reactors ....................................................................................... 13
Gas-Cooled Fast Reactor .................................................................................................. 16
Sodium-Cooled Fast Reactor ............................................................................................ 17
Lead-Cooled Fast Reactor................................................................................................. 20
Molten Salt Reactors and Fluoride Salt-Cooled High Temperature Reactors................... 22
Fusion Reactors ....................................................................................................................... 24
Major Criteria for Evaluating Unconventional Technologies........................................................ 26
Cost ......................................................................................................................................... 26
Capital Costs ..................................................................................................................... 27
Operating Costs................................................................................................................. 28
Cost Estimates for Advanced Reactors ............................................................................. 29
Size .......................................................................................................................................... 30
Safety ...................................................................................................................................... 31
Security and Weapons Proliferation Risk ................................................................................ 32
Versatility ................................................................................................................................ 34
Waste Management ................................................................................................................. 35
Environmental Effects ............................................................................................................. 37
DOE Nuclear Energy Programs .................................................................................................... 38
Office of Nuclear Energy ........................................................................................................ 40
Office of Science ..................................................................................................................... 40
National Nuclear Security Administration .............................................................................. 41
ARPA-E ................................................................................................................................... 41
Offices of Environmental Management and Legacy Management ......................................... 41
Congressional Issues ..................................................................................................................... 42
Role of the Federal Government in Technology Development ............................................... 42
Perceived Need for Advanced Nuclear Power and Competing Alternatives .......................... 43
DOE Hosting of Private-Sector Experimental Reactors ......................................................... 44
Funding of Demonstration Reactors ....................................................................................... 45
Cost Sharing ...................................................................................................................... 45
Full Funding ...................................................................................................................... 45
Federal Payments for Power and Research Use................................................................ 46
Loan Guarantees ............................................................................................................... 46
Tax Credits ........................................................................................................................ 46
Choosing Projects for Federal Funding ............................................................................ 47
Licensing Framework for New Technologies ......................................................................... 47
Power Purchase Agreements ................................................................................................... 49
Advanced Reactor Fuel Availability ....................................................................................... 50
International Organizations ........................................................................................................... 51
International Framework on Nuclear Energy Cooperation ..................................................... 51
Generation IV International Forum ......................................................................................... 51
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Figures
Figure 1. Supercritical Water-Cooled Reactor............................................................................... 13
Figure 2. Very High Temperature Reactor ..................................................................................... 16
Figure 3. Gas-Cooled Fast Reactor ............................................................................................... 17
Figure 4. Pool-Type and Loop-Type Sodium-Cooled Fast Reactors ............................................. 20
Figure 5. Lead-Cooled Fast Reactor .............................................................................................. 22
Figure 6. Molten Salt Fueled Reactor............................................................................................ 24
Tables
Table 1. Planned and Potential U.S. Advanced Reactor Demonstration Plants............................... 4
Table 2. Major Design Variables for Advanced Nuclear Technologies ........................................... 9
Table 3. Levelized Cost of Energy (LCOE) Estimates for New Power Plants Using
Selected Technologies ................................................................................................................ 30
Table 4. FY2023 Energy R&D Appropriations ............................................................................. 39
Table A-1. Existing Global Fast Reactors ..................................................................................... 53
Table A-2. Characteristics of Advanced Fission Reactors ............................................................. 53
Appendixes
Appendix. ...................................................................................................................................... 53
Contacts
Author Information........................................................................................................................ 53
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Introduction
The nuclear power industry in the United States is the largest in the world, with 92 operating
reactors, but its capacity has been nearly flat for the past three decades.1 High capital costs, low
electricity demand growth, and competition from cheaper sources of electricity, such as natural
gas and renewables, have dampened the demand for new nuclear power plants and led to the
permanent shutdown of existing reactors. Thirteen nuclear reactors have closed in the United
States during the past 10 years, although the announced retirements of two more by 2025 have
been postponed. As aging reactors reach the end of their operating licenses in 2030 and beyond,
the number of retirements is projected to increase. In addition, cost and schedule overruns have
hindered recent efforts to build new U.S. nuclear units. The only power reactors currently under
construction in the United States—two new units at the Vogtle nuclear plant in Georgia—are six
years behind schedule and more than double their original estimated cost of about $14 billion.2
All nuclear power in the United States is generated by light water reactors (LWRs), which were
commercialized in the 1950s and early 1960s and are now used throughout most of the world.
LWRs are cooled by ordinary (“light”) water, which also slows (“moderates”) the neutrons that
maintain the nuclear fission chain reaction (splitting of heavy nuclei) that releases energy.
Conventional LWRs are large—typically with 1,000 megawatts of electric generating capacity
(MWe) or more—in order to spread their high construction costs among the maximum possible
number of kilowatt-hours of electricity generated over their operating lifetime.
At the same time that conventional reactors are facing an uncertain future, some in Congress
contend that more nuclear power plants, not fewer, are needed to help reduce U.S. greenhouse gas
emissions and bring low-carbon power to the majority of the world that currently has little access
to electricity.3 Proponents of this view argue that the key to increasing the number of nuclear
power plants is investment in “advanced” nuclear technologies, which they say could address the
economic problems, safety concerns, waste management, and other issues that have stalled the
growth of conventional LWRs. Advanced reactors that could run far hotter than today’s LWRs
could be aimed at wider markets beyond electricity generation, such as production of heat for
industrial processes, hydrogen production, desalination, and heating commercial and residential
buildings.4
The Energy Act of 2020 (Division Z of P.L. 116-260) defines “advanced nuclear reactor” as a
fission reactor “with significant improvements compared to reactors operating on the date of
1 Energy Information Administration, “Nuclear Explained: U.S. Nuclear Industry,” updated April 18, 2022,
https://www.eia.gov/energyexplained/nuclear/us-nuclear-industry.php.
2 Sonal Patel, “How the Vogtle Nuclear Expansion’s Costs Escalated,” Power, September 24, 2018,
https://www.powermag.com/how-the-vogtle-nuclear-expansions-costs-escalated/?pagenum=1; and Darrell Proctor,
“Votgle Expansion Cost Jumps Again; In-Service Dates Set for 2023,” Power, July 28, 2022,
https://www.powermag.com/vogtle-expansion-cost-jumps-again-in-service-dates-set-for-2023/.
3 Some analyses have concluded that the average CO emissions rate of electricity generation must decline to a range of
2
10-25 grams CO2/kilowatt-hour (kWh) worldwide by 2050 to meet the internationally agreed-upon target of limiting
global temperature rise to 2°C. Some studies suggest there is a significant opportunity cost associated with attempting
to meet these goals without the expansion of nuclear energy capacity. See Massachusetts Institute of Technology, “The
Future of Nuclear Energy in a Carbon-Constrained World,” 2018, http://energy.mit.edu/research/future-nuclear-energycarbon-constrained-world.
4 Senate Committee on Energy and Natural Resources, Potential Non-Electric Applications of Civilian Nuclear Energy,
full committee hearing, November 4, 2021, https://www.energy.senate.gov/hearings/2021/11/full-committee-hearingon-potential-non-electric-applications-of-civilian-nuclear-energy.
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enactment” or a fusion reactor (which releases energy by forcing together the nuclei of light
isotopes).5 Examples of fission reactor improvements listed in the act include
additional inherent safety features;
lower waste yields;
improved fuel and material performance;
greater reliability;
increased resistance to nuclear weapons proliferation;
increased thermal efficiency;
reduced consumption of cooling water and other environmental impacts;
ability to integrate electricity generation and non-electric applications;
operational flexibility to change output to match demand and complement
intermittent renewable energy output or energy storage; and
modular sizes to match electricity and other energy requirements.
The definition of advanced reactors encompasses a wide range of technologies, including nextgeneration water-cooled reactors (e.g., small modular LWRs and supercritical water-cooled
reactors), non-water-cooled reactors (e.g., lead or sodium fast reactors, molten salt reactors, and
high temperature gas reactors), and fusion reactors. Some advanced reactor concepts are
relatively new, while others have been under consideration for decades and used in research, test,
and prototype reactors in the United States and around the world. Reactors using any of these
technologies that have electric generating capacity of 300 MW or below are classified as small
modular reactors (SMRs) by the International Atomic Energy Agency (IAEA).6 Proponents of
SMRs contend that their smaller size would reduce the financing costs and allow for large-scale
factory production. Some designs for improved versions of existing large LWRs could also be
considered advanced reactors under this definition if they were not in operation on the date of
enactment.
The Energy Act of 2020 authorized the Advanced Reactor Demonstration Program (ARDP)
within the Department of Energy (DOE), allowing DOE to fund up to 50% of the costs of two
commercial demonstration projects and 80% of the costs for possible future demonstration plants.
An initial appropriation of $230 million was provided for the program by the Further
Consolidated Appropriations Act, 2020 (P.L. 116-94). The Infrastructure Investment and Jobs Act
(P.L. 117-58) appropriated $2.477 billion for the program through FY2025, in addition to annual
appropriations. In the annual appropriations process, Congress provided $250 million for ARDP
in FY2022 (P.L. 117-103), the same as in FY2021, and $85 million in the Consolidated
Appropriations Act, 2023 (P.L. 117-328).
Awards for the first two demonstration plants under ARDP were announced on October 13,
2020.7 One of the award recipients, TerraPower, is proposing to build its demonstration plant on
5 P.L. 116-260, Division Z, Section 2002, enacted December 27, 2020, amended the definition of advanced nuclear
reactor in the Energy Policy Act of 2005 at 42 U.S.C. §16271(b)(1).
6 International Atomic Energy Agency, “What Are Small Modular Reactors (SMRs)?,” November 4, 2021,
https://www.iaea.org/newscenter/news/what-are-small-modular-reactors-smrs.
7 DOE Office of Nuclear Energy, “U.S. Department of Energy Announces $160 Million in First Awards under
Advanced Reactor Demonstration Program,” October 13, 2020, https://www.energy.gov/ne/articles/us-departmentenergy-announces-160-million-first-awards-under-advanced-reactor.
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the site of a closing coal-fired power plant in Wyoming.8 The other recipient, X-energy, plans to
build its demonstration plant in Washington.9
The Nuclear Regulatory Commission (NRC) is currently reviewing a design certification
application for an SMR plant designed by NuScale, to consist of up to a dozen 77 MWe reactors
in a large pool of water.10 In 2020, DOE, through a separate Office of Nuclear Energy program
from ARDP, announced a cost-shared award of up to $1.4 billion for a six-unit NuScale
demonstration plant to be built at Idaho National Laboratory (INL).11
DOE is also authorized under ARDP to provide up to 80% of the funding to develop advanced
reactor concepts for possible future demonstrations. In 2020, DOE announced five awards for
“risk reduction for future demonstration projects,” with the goal of designing and developing
advanced reactor technologies that could be licensed and deployed within 10-14 years.12
The Department of Defense (DOD) is funding a prototype mobile high-temperature gas-cooled
microreactor to provide power for military bases and other defense needs. Under a program called
Project Pele, DOD awarded a contract estimated at $300 million in June 2022 to BWX
Technologies (BWXT) for the prototype, which is to begin testing at INL in 2024. Because the 15 MWe DOD prototype microreactor will not be a commercial power plant, it will not require an
NRC license. Instead it is expected to be built and operated under DOE safety oversight with
NRC participation.13 DOE also awarded BWXT up to $85 million from the ARDP risk reduction
program to develop a commercially viable transportable high-temperature microreactor.
The CHIPS Act of 2022 (P.L. 117-167, Division A, Section 10781) authorizes a DOE advanced
nuclear reactor research, development, and demonstration grant program. In awarding the grants,
DOE is to give priority to projects that would be located at closed or closing fossil fuel power
plants and that “plan to support non-electric applications” of nuclear energy.
Planned or potential demonstration plants with committed federal funding or NRC licensing or
pre-application interactions are shown in Table 1.
8 TerraPower, “TerraPower Selects Kemmerer, Wyoming as the Preferred Site for Advanced Reactor Demonstration
Plant,” November 16, 2021, https://www.terrapower.com/natrium-demo-kemmerer-wyoming.
9 TRi Energy Partnership, “Frequently Asked Questions,” https://www.energy-northwest.com/whoweare/news-andinfo/Documents/TRi%20Energy%20Partnership%20-%20Frequently%20Asked%20Questions.pdf.
10 NRC, “Application Review Schedule for the NuScale Design,” September 20, 2022, https://www.nrc.gov/reactors/
new-reactors/smr/nuscale/review-schedule.html. NuScale has applied to increase each module’s electric generating
capacity to 77 MW. See NuScale Power, “Technology Overview,” https://www.nuscalepower.com/technology/
technology-overview.
11 DOE Office of Nuclear Energy, “DOE Approves Award for Carbon Free Power Project,” October 16, 2020,
https://www.energy.gov/ne/articles/doe-approves-award-carbon-free-power-project.
12 DOE, “Energy Department’s Advanced Reactor Demonstration Program Awards $30 Million in Initial Funding for
Risk Reduction Projects,” December 16, 2020, https://www.energy.gov/ne/articles/energy-departments-advancedreactor-demonstration-program-awards-30-million-initial.
13 Sonal Patel, “DOD Picks BWXT Design for ‘Project Pele’ Prototype Nuclear Microreactor,” Power, June 9, 2022,
https://www.powermag.com/dod-picks-bwxt-to-manufacture-project-pele-prototype-nuclear-microreactor.
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Table 1. Planned and Potential U.S. Advanced Reactor Demonstration Plants
Reactor
Designer
Technology
Reactor
Power
(Electric)
Plant Owner
DOE Funding
DOE Cost
Share
Plant Location
NRC Licensing
Status
Demonstrations with ARDP Funding
Terra Power
Sodium-cooled fast
reactor
345 MW
PacifiCorp
Up to $2.0 billion
50%
Kemmerer, WY
Pre-application
activities
X-energy
High-temperature
gas-cooled reactor
80 MW
Energy Northwest
Up to $1.2 billion
50%
Washington
Pre-application
activities
Utah Associated
Municipal Power
Systems
Up to $1.4 billion
23%
INL
77 MW standard design
application submitted
1/1/2023
Demonstrations with Other DOE Funding
NuScale
Light water SMR
77 MW
Pre-Demonstrations with ARDP Funding
Westinghouse
Heat pipe microreactor
5 MW
Westing-house
Up to $7 million
80%
Unspecified
Pre-application
activities
BWX
Technologies
Commercial hightemperature gascooled microreactor
17 MW
BWX Technologies
Up to $85 million
80%
Unspecified
None
Kairos
Fluoride-saltcooled hightemperature test
reactor
35 MW thermal
Kairos
Up to $303
million
48%
Oak Ridge, TN
Construction permit
application submitted
9/29/2021
Holtec
Water-cooled SMR
160 MW
Holtec
Up to $116
million
79%
Unspecified
Pre-application
activities
Terra Power
Molten chloride
fast reactor test
facilities
Unspeci-fied
TerraPower
Up to $90 million
80%
Everett, WA
Pre-application
activities
CRS-4
Reactor
Designer
Reactor
Power
(Electric)
Technology
DOE Funding
DOE Cost
Share
DOD
About $300
million
Funded by
DOD
Plant Owner
Plant Location
NRC Licensing
Status
Prototype Funded by DOD
BWX
Technologies
Defense hightemperature gascooled microreactor
1-5 MW
INL
DOE safety oversight
Other Designs with NRC Interactions
General
Atomics
High-temperature
gas-cooled fast
reactor
50 MW
Unspecified
No
demonstration
funding
None
Unspecified
Pre-application
activities
Terrestrial
Energy
Molten salt reactor
392 MW
Unspecified
No
demonstration
funding
None
Unspecified
Pre-application
activities
GE Hitachi
Water-cooled SMR
300 MW
Ontario Power
Generation
No
demonstration
funding
None
Clarington, Ontario
Pre-application
activities by NRC and
Canadian Nuclear
Safety Commission
Ultra Safe
Nuclear
Corporation
High-temperature
gas-cooled microreactor
15 MW thermal
University of Illinois
No
demonstration
funding
None
University of Illinois
at UrbanaChampaign
Pre-application
activities
Sources: DOE, NRC, Government Accountability Office, company websites, news accounts.
Note: Demonstration projects with announced DOE or DOD funding or with licensing application or pre-application activities listed on the NRC website. INL = Idaho
National Laboratory. The planned TerraPower demonstration near Kemmerer, WY, is at the site of closing coal plant.
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The Energy Act of 2020 also included several other provisions to support the development and
commercialization of advanced reactors. The act requires DOE to provide high-assay lowenriched uranium (HALEU)—uranium enriched in the fissile isotope U-235 between 5% and
20%—that would be required by many advanced reactor designs, including the two ARDP
demonstrations. The act authorizes appropriations for major DOE nuclear energy programs,
including advanced reactor research; demonstration of nuclear energy systems integrated with
non-electricity applications, such as hydrogen production and industrial heat; and nuclear fuel
cycle R&D.
Tax credits for advanced nuclear reactors and other new zero-carbon power plants were included
in the law commonly referred to as the Inflation Reduction Act (IRA, P.L. 117-169). The owners
of qualifying plants can receive a 10-year electricity production tax credit of up to 2.6
cents/kilowatt-hour (adjusted for inflation) or a 30% investment tax credit. IRA also included
$700 million for DOE to develop supplies of HALEU.
The Nuclear Energy Innovation Capabilities Act of 2017 (NEICA, P.L. 115-248) required DOE to
take several actions to support advanced reactor development, including establishment of the
National Reactor Innovation Center to enable testing and demonstration of private-sector reactor
concepts at DOE sites. The Nuclear Energy Innovation and Modernization Act (NEIMA, P.L.
115-439), signed January 14, 2019, required NRC to develop a regulatory framework that could
be used for advanced nuclear technologies.
Advocates of nuclear power cite a variety of reasons in addition to concern about greenhouse gas
emissions for preserving and expanding the U.S. nuclear industry. They contend that a robust
domestic nuclear energy industry would contribute to such goals as energy security and
diversification, electricity grid resilience and reliability, promotion of a domestic nuclear
component manufacturing base and associated exports, clean air, and preservation and
enhancement of geopolitical influence. The U.S. Navy uses nuclear energy to power submarines
and aircraft carriers. Some observers have suggested that the Navy and other national security
organizations benefit from maintaining a strong domestic nuclear energy industry, which provides
a post-military career path for many naval reactor personnel, as well as expanding the base of
qualified engineers and technicians, and strengthening the infrastructure for training and
knowledge transfer.14 Geopolitical arguments focus particularly on concerns that U.S. influence
on the international nuclear weapons nonproliferation regime would diminish without a robust
domestic nuclear power industry and technology exports.15
Not all observers are optimistic about the potential safety, affordability, proliferation resistance,
and sustainability of advanced reactors.16 Because many of these technologies are in the
conceptual or design phases, the potential advantages of these systems are unproven.17 Testing
14 Nuclear Energy Institute, “Navy Leaders Say Commercial Nuclear Industry Benefits National Security, Innovation,”
Electric Energy Online, October 5, 2018, https://electricenergyonline.com/social/fj1y/article/energy/article/_/0/724534/
Navy-Leaders-Say-Commercial-Nuclear-Industry-Benefits-National-Security-Innovation.htm.
15 Center for Strategic and International Studies, Restoring U.S. Leadership in Nuclear Energy: A National Security
Imperative, June 2013, https://csis-website-prod.s3.amazonaws.com/s3fs-public/legacy_files/files/publication/
130614_RestoringUSLeadershipNuclearEnergy_WEB.pdf.
16 For example, a report by the Intergovernmental Panel on Climate Change (IPCC) states that nuclear energy, whether
derived from existing or advanced technologies, poses a risk for accidents, lacks agreed-upon solutions for long-term
waste storage, has negative downstream impacts from uranium mining, poses a constant threat of weapons
proliferation, and has been associated by some studies with increased risk of childhood leukemia for populations living
near nuclear plants. IPCC, “Global Warming of 1.5°C,” 2018, Ch. 5, pp. 52, 57, https://www.ipcc.ch/sr15.
17 Beginning in the 1950s, the U.S. government built experimental and, in some cases, commercial versions of reactors
utilizing some of the same advanced reactor technologies discussed in this report. These demonstrations provided
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and demonstration at a commercial scale, and possibly the operation of multiple plants, would be
required to determine the validity of advocates’ claims, particularly related to costs. Many
environmental advocates contend that nuclear power would not be necessary to decarbonize
world energy supplies, and that public policy should instead focus on renewable energy and
energy efficiency.18
The U.S. advanced nuclear industry has expanded in recent years to encompass an array of
developers, suppliers, and supporting institutions. By one count, at least 25 U.S. companies were
developing advanced nuclear reactor technologies as of July 2021.19 Some have projected that the
first U.S. advanced reactor could be providing electricity to the grid by the late 2020s. For
example, the advanced reactor company NuScale has predicted, “The first NuScale Power
Module will begin generating power in 2029.”20
This report discusses the history of advanced reactor technologies, briefly describes major
categories of advanced reactors, provides an overview of federal programs on advanced nuclear
technology, and discusses current issues and legislation.
Advanced Reactor Technologies
Advanced or unconventional reactor designs seek to use combinations of new and existing
technologies and materials to improve upon earlier generations of nuclear reactors in one or more
of the following areas: cost, safety, security, waste management, and versatility. To achieve these
improvements, advanced designs may incorporate one or more of the following characteristics:
inherent or passive safety features, simplified or modular designs, enhanced load-following
capabilities, high-temperature stability, fast neutron spectrums, and “closed” fuel cycles (see text
box on Fast Reactors). Advanced reactor technologies are often referred to as “Generation IV”
nuclear reactors, with existing commercial reactors constituting “Generation III” or, for the most
recently constructed reactors, “Generation III+.”
Advanced reactor designs may be grouped into three primary categories:
Advanced water-cooled reactors, which provide evolutionary improvements to
proven water-based fission technologies through innovations such as simplified
design, smaller size, or enhanced efficiency;
historical data and experience for the development of the current wave of advanced reactor designs. While federal
funding for nuclear power research was largely consolidated to relatively few sites (e.g., Oak Ridge and Idaho National
Laboratories), federal spending for environmental remediation, decommissioning and decontamination (D&D), and
long-term stewardship continues at former nuclear research sites, such as the Energy Technology Engineering Center at
the Santa Susana Field Laboratory in California and the Fort St. Vrain Site in Colorado. Part of the costs for carrying
out nuclear power research is the D&D and remediation costs for the contaminated facilities resulting from that
research.
18 Heinrich Boll Stiftung, “Energy Transitions Around the World,” April 12, 2019, https://us.boell.org/energytransition-around-world. For a discussion of U.S. electricity options, see CRS Insight IN11065, An Electric Grid Based
on 100% Renewable Energy?, by Richard J. Campbell.
19 DOE Gateway for Accelerated Innovation in Nuclear (GAIN), Advanced Nuclear Directory: Developers, Suppliers
and National Laboratories, July 1, 2021, https://gain.inl.gov/SiteAssets/Funding%20Opportunities/
GAINAdvancedNuclearDirectory-Seventh%20Edition_07.01.2021-R1.pdf.
20 NuScale, “Carbon Free Power Project,” company web page, viewed November 12, 2021,
https://www.nuscalepower.com/projects/carbon-free-power-project.
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Non-water-cooled reactors, which are fission reactors that use materials such as
liquid metals (e.g., sodium and lead), gases (e.g., helium and carbon dioxide), or
molten salts as coolants instead of water; and
Fusion reactors, which seek to generate energy by joining small atomic nuclei, as
opposed to fission reactors, which generate energy by splitting large atomic
nuclei.
Fission reactors can also be classified as fast neutron reactors and thermal neutron reactors, as
described in the box below. They also may vary in their use of fuels, such as by irradiating
thorium to produce the fissile isotope uranium-233.
Small modular reactors, with electric generating capacity of no more than 300 MW,21 can be in
any of those categories. According to DOE, SMRs “employ modular construction techniques,
ship major components from factory fabrication locations to the plant site by rail or truck, and
include designs that simplify plant site activities required for plant assembly.”22 Microreactors are
relatively small-capacity SMRs, defined by DOE as producing 1-20 megawatts of thermal energy
(MWt), which could be used directly as heat for industrial processes or to generate electricity. In
theory, microreactors could be transported by truck and installed at a remote location or military
base, according to DOE.23
Many widely differing advanced reactor designs are conceivable, with major variables including
the type of coolant, fuel, size, and other examples shown in Table 2. An advanced reactor design
could use one or more of the features from each column. For example, the planned X-energy
demonstration plant in Washington would have these characteristics, among others: helium
coolant, thermal neutrons moderated by graphite, HALEU fuel in TRISO pebbles, high burnup,
and the size of an SMR.24
21 Compared with typically 1,000 MW or more for existing conventional LWRs.
22 U.S. Department of Energy, “Advanced Small Modular Reactors (SMRs),” https://www.energy.gov/ne/nuclear-
reactor-technologies/small-modular-nuclear-reactors.
23 According to DOE, the setup time for a transportable microreactor would range from weeks to months. DOE, “What
Is a Nuclear Microreactor?,” February 26, 2021, https://www.energy.gov/ne/articles/what-nuclear-microreactor.
According to Defense News, the Project Pele microreactor “must be designed to operate within three days of delivery
and be safely removed in as few as seven days if needed.” Aaron Mehta, Defense News, Portable Nuclear Reactor
Project Moves Forward at Pentagon,” March 23, 2021, https://www.defensenews.com/smr/energy-and-environment/
2021/03/23/portable-nuclear-reactor-project-moves-forward-at-pentagon.
24 X-energy, “X-energy’s Reactor: Xe-100,” https://x-energy.com/reactors/xe-100.
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Table 2. Major Design Variables for Advanced Nuclear Technologies
Fission reactor designs could use one or more features from each column
Coolant
Light water
Heavy water
Liquid metal
Molten salt
Helium
CO2
Neutron
Energy
Thermal
Fast
Moderator
Fuel
Material
Light water
Heavy water
Graphite
None
LEU
HALEU
Plutonium
Thorium
Fuel Form
Fuel Cycle
Reactor
Size
Oxide, metal clad
TRISO pebble bed
Other TRISO
Molten salt
Metal
Carbide
Ceramic matrix
Open
High burnup
Closed
Microreactor
SMR
Conventional
Source: National Academies of Sciences, Engineering, and Medicine, DOE, IAEA, World Nuclear Association.
Notes: Light water is ordinary water; heavy water has an extra neutron in the hydrogen component. Examples
of liquid metal coolants are sodium and lead. A reactor with no moderator is a fast reactor. LEU=low enriched
uranium; HALEU=high-assay low enriched uranium (5%-10% enriched in U-235). Thorium in fuel must first be
transmuted to uranium-233 to be fissile. In an open fuel cycle, spent nuclear fuel is intended for permanent
disposal. In the high-burnup cycle, fuel produces power for a long period before permanent disposal but is not
reprocessed. In a closed fuel cycle, spent fuel is reprocessed to separate uranium, plutonium, and other materials
that can be used in new fuel.
Advanced reactor concepts may be characterized along a continuum of technological maturity.
Light water-cooled SMRs, high-temperature gas-cooled reactors, and sodium-cooled fast reactors
are considered to be among the most mature of the unconventional reactor technologies.25 Molten
salt reactors, gas-cooled fast reactors, and fusion reactors are generally considered to be further
from commercialization.
Expert estimates of timeframes for commercialization of these technologies range widely, from
the late 2020s or early 2030s for the first small modular LWRs to mid-century or later for some
advanced reactor concepts, such as molten salt reactors and gas-cooled fast reactors. Companies
developing similar reactor technologies may be at different stages of design and manufacturing
readiness. Planned demonstrations of molten salt reactors, for example, range from the late 2020s
to the 2040s.26
Fast Reactors
A large proportion of advanced reactor concepts are fast neutron reactors (FNRs or fast reactors), which have
fundamental differences from conventional LWRs. Some of these unique characteristics could provide advantages
over conventional nuclear technology, although there are potential drawbacks as well.
Thermal nuclear reactors—the majority of those currently in operation worldwide—rely on a “moderator” to
slow the movement of neutrons in the nuclear chain reaction. Slower-moving neutrons, or thermal neutrons, have a
relatively high likelihood of producing a new fission reaction in the fissile uranium isotope U-235, which makes up
about 0.7% of natural uranium. The remaining 99.3% is non-fissile U-238. Nuclear fuel is usually “enriched” to
increase the percentage of U-235. Because thermal neutrons readily induce fission, thermal reactors can be fueled
by uranium with low levels of enrichment or in some designs by natural (unenriched) uranium.
LWRs are thermal reactors that use ordinary (light) water as a moderator and coolant. Thermal neutrons in
LWRs can sustain a nuclear chain reaction with low-enriched uranium (LEU) of between 3% and 5% U-235.
25 Massachusetts Institute of Technology, “The Future of Nuclear Energy in a Carbon-Constrained World,” p. xxii. Gen
IV International Forum, “Technology Systems,” November 15, 2018, https://www.gen-4.org/gif/jcms/c_40486/
technology-systems.
26 World Nuclear Association, “Molten Salt Reactors,” May 2021, http://www.world-nuclear.org/information-library/
current-and-future-generation/molten-salt-reactors.aspx.
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Reactors that are cooled and moderated by heavy water (water whose hydrogen component includes a neutron)
can operate on natural uranium, because heavy water absorbs fewer neutrons than light water, freeing additional
neutrons to sustain the chain reaction. Reactors using graphite as a moderator can also operate with LEU.
Fast reactors, in contrast, do not use a moderator to slow neutron movement. Fast neutrons have a lower
likelihood of inducing fission than thermal neutrons, so to sustain a chain reaction, the fuel must have relatively
high concentrations of U-235 or other fissile isotopes. For fast reactor uranium fuel, enrichment in U-235 must at
least be near the upper LEU limit of just below 20%. Current reactor designs avoid uranium enrichment of 20%
and above, because it is classified as high-enriched uranium (HEU)—a potential weapons material that is subject to
additional nonproliferation safeguards. LEU enriched above 5% (the maximum level used by LWRs) is called highassay low-enriched uranium (HALEU). Production of HALEU for demonstrations of fast reactors and other
advanced reactor designs is a DOE priority, as noted above. FNRs also may use plutonium as a primary fuel.
Plutonium typically has a high percentage of fissile isotopes (primarily Pu-239) and at high neutron energies
produces more neutrons per fission event than uranium.
Fast reactor coolants must have no neutron moderating effect. Possible coolants include molten salts, liquid metals
such as sodium, lead, and lead-bismuth, and gases such as helium or carbon dioxide. To date, most experimental
FNRs that have been built used sodium as a coolant.
Liquid metal coolants transfer heat from nuclear fuel more efficiently than water and operate at low pressure
(because they remain liquid at high temperatures). The physics of fast reactors dampens the nuclear chain reaction
when the temperature rises, preventing the fuel from producing more heat than the coolant can safely remove.
Proponents of fast reactors contend that those characteristics would greatly reduce the likelihood of accidental
fuel damage and any resulting release of radioactive material.
Non-fissile U-238 can be transmuted to fissile Pu-239 through neutron capture, which occurs at a higher rate in
fast reactors than in thermal reactors. If a reactor produces more fissile material (such as Pu-239) than it
consumes (such as U-235), it is considered to be a “breeder.” A reactor that produces less than it consumes is a
“burner” or “converter.” Most breeder reactors are fast reactors because of their neutron capture efficiency, but
fast reactors can be configured as either breeders or burners.
Fast neutrons are also more effective than thermal reactors at fissioning plutonium and actinides, which are
converted to relatively short-lived fission products such as cesium 137 and strontium 90. This effectiveness at
fissioning a wide variety of isotopes allows fast reactors to operate well with fuel made from the plutonium and
uranium separated during the reprocessing (or “recycling”) of spent nuclear fuel. Unlike thermal reactors, fast
reactors could theoretically re-use their spent fuel indefinitely—disposing only of the highly radioactive fission
products. Such a “closed” fuel cycle would be in contrast to the current “open” or “once through” fuel cycle, in
which spent fuel would be permanently disposed of in a deep repository without reprocessing.
In theory, the closed fuel cycle (with the re-use of uranium and plutonium) could extend fuel supplies and
potentially reduce the duration of the radioactive hazard of nuclear waste from more than a million years to less
than 1,000 years. If breeder reactors were employed to maximize the conversion of U-238 to plutonium, the
amount of energy released from a given quantity of natural uranium could be increased by a factor of 60.27
The closed fuel cycle has major drawbacks that would need to be addressed. One is that the separation of
plutonium from spent fuel is widely perceived as a nuclear weapons proliferation risk, because plutonium is a key
weapons material. As a result, U.S. policy has been based primarily on the once-through fuel cycle since the mid1970s. Another drawback is that reprocessing spent fuel to separate uranium, plutonium, and waste products can
require large, costly facilities that generate large volumes of low- and high-level waste that, while shorter-lived
than spent fuel, still must be treated and disposed of. Potential waste generation by spent fuel reprocessing has
been a continuing issue in Congress, which requested a report on the topic from the National Academies of
Sciences, Engineering, and Medicine (NASEM) that was released in December 2022.28
27 Lisa Zyga, “Why Nuclear Power Will Never Supply the World’s Energy Needs,” PhysOrg.com, May 11, 2011,
https://phys.org/news/2011-05-nuclear-power-world-energy.html.
28 National Academies of Sciences, Engineering, and Medicine, Merits and Viability of Different Nuclear Fuel Cycles
and Technology Options and the Waste Aspects of Advanced Nuclear Reactors, December 2022,
https://nap.nationalacademies.org/catalog/26500/merits-and-viability-of-different-nuclear-fuel-cycles-and-technologyoptions-and-the-waste-aspects-of-advanced-nuclear-reactors. The NASEM study was mandated by the explanatory
statements for P.L. 116-94 and P.L. 116-260.
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FNRs are not a new concept. The first FNR was built in 1946 in the United States,29 and the world’s first reactor
to generate electricity was a U.S.-built fast reactor.30 Since the 1940s, there have been more than 20 fast reactors
built—including 10 in the United States—mostly for either experimental or demonstration purposes.31 Five fast
reactors are currently in operation globally.32 Despite that experience, the commercial viability of FNRs, as with
other types of advanced reactors, remains uncertain.
Advanced Water-Cooled Reactors
Small Modular Light Water Reactors
Small modular reactors are defined by DOE and IAEA as reactors with an electric generating
capacity of up to 300 MW, as opposed to the average capacity of existing U.S. commercial
reactors of about 1,000 MW. Light water reactor SMR designs are based on existing commercial
LWR technology but are generally small enough to allow all major reactor components to be
placed in a single pressure vessel. For example, in a pressurized water reactor, such as the
NuScale design described below, cooling water is kept under pressure so that it will not boil and
circulates through heat exchangers (steam generators) in the reactor pressure vessel. The steam
generators transfer heat to a secondary loop of cooling water that is allowed to boil to make steam
for power generation.
The reactor vessel and its components are designed to be assembled in a factory and transported
to the plant site for installation, potentially reducing construction time and costs from those of
large LWRs. If large numbers of identical SMRs were ordered, mass production could further
reduce manufacturing costs and construction schedules, according to proponents of the
technology.
Shortening the timeframe before a new reactor begins producing revenue could reduce interest
payments and shorten payback periods. In addition, each SMR would require a fraction of the
capital investment of a large conventional nuclear unit, further reducing the financial risk to plant
owners. Some observers have suggested that the smaller size of SMRs would reduce the
economies of scale available to larger reactors, potentially negating any SMR cost advantages.33
DOE has awarded up to $1.4 billion for a light water SMR demonstration plant at INL that would
consist of six 77 MWe reactor modules designed by NuScale Power. The plant, called the Carbon
Free Power Project, would be owned and operated by the Utah Associated Municipal Power
29 Clementine, a 25 kWt (kilowatts of thermal energy) mercury-cooled experimental fast reactor, was built at Los
Alamos to produce plutonium for nuclear weapons.
30 Experimental Breeder Reactor I (EBR-I), a 1.2 MWt (megawatts of thermal energy) sodium-cooled experimental fast
reactor, was built in 1951 in Idaho and produced both plutonium and electrical power. For a history of the U.S. fast
breeder reactor program, see Thomas B. Cochran, et al., Fast Breeder Reactor Programs, History and Status,
International Panel on Fissile Materials, February 2010, https://fissilematerials.org/library/rr08.pdf.
31 A majority of these were breeder reactors, intended to produce more nuclear fuel than they consumed. The 10 U.S.
FNRs were Clementine, S1G, S2G, LAMPRE-I, EBR-I, EBR-II, Fermi I, SEFOR, the Fast Source Reactor, and the
Fast Flux Test Facility.
32 Three are in Russia, one in China, and one in India. All are sodium-cooled (see “Sodium-Cooled Fast Reactor”).
Japan has two FNRs that were in operation within the past decade, but are currently inactive. Several others are in
various stages of development or construction. (World Nuclear Association, “Fast Neutron Reactors,” August 2021,
http://www.world-nuclear.org/information-library/current-and-future-generation/fast-neutron-reactors.aspx.)
33 Ahmed Abdulla et al., “Expert Assessments of the Cost of Light Wter Small Modular Reactors,” PNAS, vol. 110, no.
24, May 28, 2013, https://www.pnas.org/doi/10.1073/pnas.1300195110.
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Systems (UAMPS) and start generating power by 2029.34 The plant’s SMR modules would be colocated in a central pool of water, which serves as a heat sink and passive cooling system. The
DOE funding is estimated to cover about 23% of the cost of building the demonstration plant.35
As with other SMR concepts, the major components of the NuScale plant are designed to be
factory-fabricated and shipped to the plant site for installation.36
A light water SMR design by GE Hitachi, BWRX-300, is proposed for demonstration by Ontario
Power Company at its Darlington Plant in Clarington, Ontario. The BWRX-300 is a 300 MW
version of the company’s large boiling water reactors, in which cooling water in the reactor vessel
is directly allowed to boil (rather than going through a steam generator) to make steam for power
generation.37 The Tennessee Valley Authority is considering construction of a BWRX-300 plant at
its Clinch River site in Tennessee.38 The design is currently undergoing pre-application reviews at
NRC and the Canadian Nuclear Safety Commission.39
Holtec International has received a DOE ARDP pre-demonstration grant for its SMR-160 design
(a 160 MW water-cooled SMR). The design is currently undergoing NRC pre-application review
and has completed Phase 1 of the Canadian Nuclear Safety Agency Vendor Design Review.
Holtec has announced that it might build the first SMR-160 module at the site of the closed
Oyster Creek nuclear power plant, which is owned and being decommissioned by a Holtec
subsidiary.40
Supercritical Water-Cooled Reactor
The supercritical water-cooled reactor (SCWR) is a high-temperature variant of existing LWR
technologies. SCWRs would use supercritical water—water which has been brought to a
temperature and pressure at which the liquid and vapor states are indistinguishable—to improve
plant efficiency (which may approach 44% in SCWRs, compared with about 33% for current
reactors). As in a conventional boiling water reactor (BWR), liquid water would pass upward
34 UAMPS, “Carbon Free Power Project,” https://www.uamps.com/Carbon-Free.
35 Government Accountability Office, Nuclear Energy Projects: DOE Should Institutionalize Oversight Plans for
Demonstrations of New Reactor Types, GAO-22-105394, September 2022, p. 9, https://www.gao.gov/assets/gao-22105394.pdf. The report notes that, including previous funding, DOE could provide up to $1.9 billion for the
demonstration plant.
36 This does not include civil structures and major site preparation work, which have been identified by an MIT study
as the primary contributors to construction costs in conventional nuclear plants built in the United States. (See section
on “Cost.”)
37 GE Hitachi, “The BWRX-300 Small Modular Reactor,” https://nuclear.gepower.com/build-a-plant/products/nuclearpower-plants-overview/bwrx-300.
38 Tennessee Valley Authority, “TVA Board Authorizes New Nuclear Program to Explore Innovative Technology,”
February 10, 2022, https://www.tva.com/newsroom/press-releases/tva-board-authorizes-new-nuclear-program-toexplore-innovative-technology.
39 NRC, “GEH BWRX-300,” September 21, 2022, https://www.nrc.gov/reactors/new-reactors/smr/licensing-activities/
pre-application-activities/bwrx-300.html; Canadian Nuclear Safety Commission, “Charter: Collaboration on GE
Hitachi’s BWRX-300 Design,” September 2022, https://nuclearsafety.gc.ca/eng/resources/international-cooperation/
international-agreements/cnsc-usnrc-smr-advanced-reactor-charter.cfm.
40 Holtec International, “Overview,” https://holtecinternational.com/products-and-services/smr/technology/overview;
NRC, “SMR-160,” October 5, 2022, https://www.nrc.gov/reactors/new-reactors/smr/licensing-activities/preapplication-activities/holtec.html; DOE, “5 Advanced Reactor Designs to Watch in 2030,” March 17, 2021,
https://www.energy.gov/ne/articles/5-advanced-reactor-designs-watch-2030; Holtec International, “Holtec and Hyundai
Engineering and Construction Completed Workshop on SMR-160 Balance of Plant Design,” February 22, 2022,
https://holtecinternational.com/2022/02/22/holtec-and-hyundai-engineering-and-construction-completed-workshop-onsmr-160-balance-of-plant-design.
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through the reactor core and turn directly to steam, which would drive a turbine-generator
(Figure 1). The superheated conditions would eliminate the need in current BWRs for reactor
coolant pumps and steam separators and dryers.41 Supercritical water has already been used to
boost plant efficiency in some advanced coal- and gas-fired power plants. SCWRs could be
designed to operate in either the fast or thermal neutron spectrums, and to use either light or
heavy water as the coolant and/or moderator. Organizations in Canada, China, the European
Union, Japan, and Russia are developing SCWRs.42
Figure 1. Supercritical Water-Cooled Reactor
Source: U.S. Department of Energy, modified by CRS.
Non-Water-Cooled Reactors
High Temperature Gas Reactors
High temperature gas reactors (HTGRs), including very high temperature gas reactors (VHTRs),
are helium-cooled, graphite-moderated thermal reactors. As their names imply, they would
operate at higher coolant outlet temperatures than most existing reactors—700°-1,000°C
compared with 330°C for existing LWRs.43 This higher temperature threshold allows for the
41 Gen IV International Forum, “Supercritical-Water-Cooled Reactor (SCWR),” viewed November 9, 2022,
https://www.gen-4.org/gif/jcms/c_9360/scwr.
42 Ibid.
43 Some sources differentiate between HTGRs and VHTRs based on their outlet temperatures, considering any reactor
that achieves a range of 900°-1,000°C to be a VHTR, with the rest being considered HTGRs. Others use these terms
interchangeably. The precise outlet temperature of a given reactor determines the types of process heat services the
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provision of heat for industrial processes, such as the cogeneration of electricity and hydrogen,
and high-temperature processes in the iron, oil, and chemical industries. While previous R&D
programs focused on achieving very high outlet temperatures, more recently the focus has shifted
to reactor designs with more modest outlet temperatures (700°-850°C), based on the assessment
that lower temperature reactors may be more commercially viable in the short term and involve
fewer technical risks.44
A key feature of these reactors is their fuel, called TRISO fuel, which is composed of poppy seedsized fuel particles that have been encased in silicon carbide and other highly heat-resistant
coatings.45 Coupled with the high heat capacity of the graphite moderator, the reactor and its fuel
are designed to withstand the maximum core heat attainable if core cooling is lost during an
accident. Therefore, according to HTGR proponents, the loss of active cooling systems would not
result in a core meltdown and radioactive releases to the environment.
Reactors using TRISO fuel are being designed without containment structures to retain
radioactive releases, because the fuel coatings are considered to be “functional containments” that
serve the same purpose. According to X-energy, “With triple-coated layers, each particle is its
own containment system and retains fission products under all reactor conditions and
temperatures.46
There are two primary design variants: In one, the TRISO fuel particles are formed into
cylindrical fuel elements and placed into prismatic graphite blocks (Figure 2). In the other
variant, the TRISO fuel particles are embedded in billiard ball-sized graphite spheres, or
“pebbles,” that are loaded into the core to form a “pebble bed.” The spheres are steadily removed
from the bottom of the reactor, tested for their level of burnup, and returned to the top of the
reactor if they are still viable as fuel and replaced if not. In both variants, the graphite serves as a
neutron moderator. Many HTGRs have been designed as SMRs.
HTGRs are among the most technologically mature of the advanced reactor concepts. Since the
1960s a number of experimental and commercial HTGRs have been built in multiple countries,
including the United States, United Kingdom, Japan, Germany, and China.47 A 210 MW, tworeactor pebble bed HTGR plant in China was connected to the electric grid on December 20,
2021.48 A U.S. HTGR demonstration called the Next Generation Nuclear Plant (NGNP) was
authorized by the Energy Policy Act of 2005 (P.L. 109-58), although the project was halted in
2011.
reactor can provide.
44 Gen IV International Forum, “Very-High-Temperature Reactor (VHTR),” viewed November 9, 2022,
https://www.gen-4.org/gif/jcms/c_42153/very-high-temperature-reactor-vhtr.
45 TRISO fuel is short for tristructural isotropic fuel, in which a kernel of uranium is surrounded by layers of porous
carbide, silicon carbide, and pyrolitic carbon. TRISO fuel can be formed into cylindrical fuel pellets for insertion into
graphite fuel blocks in a prismatic reactor, or into billiard-ball-sized spheres for a pebble bed reactor. For a diagram,
see Idaho National Laboratory, “Fuel Development and Qualification,” https://art.inl.gov/trisofuels/SitePages/
Home.aspx.
46 For example, see X-energy, Xe-100 Principal Design Criteria Licensing Topical Report, Table 5, July 8, 2022; and
X-energy, “US Department of Energy’s Advanced Reactor Demonstraton Program,” https://x-energy.com/ardp.
47 Historically, two commercial HTGRs have operated in the United States: The Peach Bottom 1 commercial reactor
operated from 1967 to 1988 in Pennsylvania, and the Fort St. Vrain commercial reactor operated from 1979 to 1989 in
Colorado. Some gas reactors have used carbon dioxide as a coolant.
48 World Nuclear News, “Demonstration HTR-PM Connected to Grid,” December 21, 2021, https://www.worldnuclear-news.org/Articles/Demonstration-HTR-PM-connected-to-grid.
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In 2015, DOE awarded X-energy $40 million over six years to develop a modular pebble bed
HTGR design.49 Under ARDP, the company received a 50% cost-shared award of $1.2 billion to
build a commercial scale demonstration plant in Washington.50 The project includes a TRISO fuel
fabrication plant in Oak Ridge, TN.51
HTGR microreactor technology is being developed by BWX Technologies (BWXT). In June
2022, DOD awarded BWXT an approximately $300 million contract to build a TRISO-fueled
HTGR microreactor at INL. The prototype is to be transportable in standard shipping containers
and be moveable to different locations. It is to generate 1-5 MWe to power forward operating
bases and other military facilities. In addition to hosting the prototype reactor, DOE is to provide
safety oversight, fuel, technical assistance, and other support, fully funded by DOD.52
In a separate project, DOE awarded an 80% cost-shared contract to BWXT in December 2020
under ARDP to reduce the technological risk of potential future demonstrations. Under the award,
BWXT is to develop the technology for a transportable 17 MWe HTGR microreactor for civilian
applications, which would be licensed by NRC. DOE is providing funding of up to $89 million
over seven years, but the award does not include demonstration funding.53
Ultra Safe Nuclear Corporation is working with the University of Illinois Urbana-Champaign in
conducting NRC pre-application activities for an HTGR test microreactor, which would have 15
MW of thermal power.54 Ultra Safe opened a pilot facility in Oak Ridge, TN, to produce TRISO
fuel for the reactor in August 2022.55
Another example of a U.S. company developing HTGRs is HolosGen, which is developing a
transportable reactor with generating capacity ranging from 3 MWe to 81 MWe. It is based on
aircraft nuclear propulsion systems studied by the U.S. Atomic Energy Commission (a
predecessor of DOE) in the 1950s.56
49 DOE Office of Nuclear Energy, “X-energy Completes $40 Million Project to Further Develop High-Temperature
Gas Reactor,” August 23, 2022, https://www.energy.gov/ne/articles/x-energy-completes-40-million-project-furtherdevelop-high-temperature-gas-reactor.
50 Government Accountability Office, Nuclear Energy Projects: DOE Should Institutionalize Oversight Plans for
Demonstrations of New Reactor Types, GAO-22-105394, September 2022, p. 9, https://www.gao.gov/assets/gao-22105394.pdf. The report notes that DOE provided an additional $19 million for design and licensing of a TRISO fuel
fabrication facility through FY2022.
51 X-energy, “TRISO-X Breaks Ground on North America’s First Commercial Advanced Nuclear Fuel Facility,”
October 13, 2022, https://x-energy.com/media/news-releases/triso-x-breaks-ground-on-north-americas-firstcommercial-advanced-nuclear-fuel-facility.
52 World Nuclear News, “BWX Technologies Selected to Build Project Pele Microreactor,” June 9, 2022,
https://www.world-nuclear-news.org/Articles/BWX-Technologies-selected-to-build-Project-Pele-mi; and email from
DOE Office of Congressional Affairs, November 1, 2022.
53 DOE Office of Nuclear Energy, “Energy Department’s Advanced Reactor Demonstration Program Awards $30
Million in Initial Funding for Risk Reduction Projects,” December 16, 2020, https://www.energy.gov/ne/articles/
energy-departments-advanced-reactor-demonstration-program-awards-30-million-initial; and email from DOE Office
of Congressional Affairs, November 1, 2022.
54 NRC, “University of Illinois at Urbana-Champaign,” October 3, 2022, https://www.nrc.gov/reactors/new-reactors/
advanced/licensing-activities/pre-application-activities/university-of-illinois-at-urbana-champaign.html.
55 Ultra Safe Nuclear Corporation, “Ultra Safe Nuclear Corporation Announces the Opening of Pilot Fuel
Manufacturing Facility in Oak Ridge, Tenn.,” August 19, 2022, https://www.usnc.com/ultra-safe-nuclear-corporationannounces-the-opening-of-pilot-fuel-manufacturing-facility-in-oak-ridge-tenn.
56 HolosGen, http://www.holosgen.com/.
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Figure 2.Very High Temperature Reactor
Prismatic core
Source: U.S. Department of Energy, modified by CRS.
Gas-Cooled Fast Reactor
Gas-cooled fast reactors (GFRs) would be high-temperature fast reactors using helium as a
primary coolant (Figure 3). The primary difference between the HTGR (see above) and the GFR
is the neutron spectrum: HTGRs operate in the thermal spectrum, while GFRs operate in the fast
spectrum. Therefore, the GFRs would not require the graphite moderator of HTGRs to slow the
neutrons. The GFR could use a closed U-Pu fuel cycle in which the plutonium and uranium could
be recycled from the spent fuel to provide a greatly expanded fuel source if configured as a
breeder (with the potential nonproliferation and waste drawbacks noted in the Fast Reactors box
above). GFRs would have operating temperatures similar to those of HTGRs—850°C compared
to 330°C for existing LWRs—making them suitable for providing process heat for industrial
purposes, in addition to producing electric power. GFRs are considered experimental technology,
because none have been built to date.57
General Atomics received a $24.8 milliion cost-shared DOE award in January 2021 under its
Advanced Reactor Concepts program to develop a conceptual design for a 50 MW gas-cooled
fast reactor in collaboration with the French company Framatome, and is currently engaged in
57 NASEM, Merits and Viability of Different Nuclear Fuel Cycles of Advanced Nuclear Reactors, p. 64.
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NRC pre-application activities.58 A consortium of European countries, including the Czech
Republic, Hungary, Poland, and Slovakia, is jointly developing a conceptual GFR design.59
Figure 3. Gas-Cooled Fast Reactor
Source: U.S. Department of Energy, modified by CRS.
Sodium-Cooled Fast Reactor
Along with HTGRs, sodium-cooled fast reactors (SFRs) are among the most technologically
mature of the unconventional nuclear concepts. SFRs use fast reactor technology with liquid
sodium metal as the primary coolant. The use of a liquid metal as the coolant allows the primary
coolant circuit to operate under lower, near-atmospheric pressure conditions. In addition, even in
an emergency without backup electricity, the high heat-transfer properties of liquid sodium (100
times greater than water) would allow for passive cooling through natural circulation.60 The SFR
coolant outlet would reach a temperature of 500°-550°C. This lower temperature (compared with
850°C for the GFR) would allow for the use of materials that have been developed and proven in
58 General Atomics, “General Atomics Selected for the Department of Energy’s Advanced Reactor Concepts-20
Program,” January 13, 2021, https://www.ga.com/general-atomics-selected-for-the-department-of-energys-advancedreactor-concepts-20-program; and NRC, “Fast Modular Reactor,” November 8, 2022, https://www.nrc.gov/reactors/
new-reactors/advanced/licensing-activities/pre-application-activities/general-atomics.
59 V4G4 Centre of Excellence, “Allegro Project Overview,” February 2021, https://snetp.eu/wp-content/uploads/2021/
02/Presentation_Branislav-Hatala-Petr-Vacha.pdf.
60 U.S. Department of Energy, Office of Nuclear Energy, “Sodium-cooled Fast Reactor (SFR) Technology and Safety
Overview,” February 18, 2015, https://gain.inl.gov/SiteAssets/Fast%20Reactors/SFRNRCTechnologyandSafetyOverview18Feb15.pdf.
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prior fast reactors. SFRs come in two main design variants: loop-type and pool-type designs (see
Figure 4). In the pool-type SFR, the reactor core and primary heat exchanger are immersed in a
single pool of liquid metal, while the loop-type houses the primary heat exchanger in a separate
vessel. SFR technologies are conducive to modularization.
A disadvantage of using sodium as a coolant is that it reacts violently with both air and water. As
a result, the primary sodium coolant system (which contains highly radioactive sodium) is often
isolated from the steam generation system by an intermediary coolant to prevent a release of
radioactivity in the case of an accident. This adds costs and complexity to the system, complicates
maintenance and refueling, and introduces an additional safety concern. Fires resulting from
sodium leaks have caused shutdowns in several SFRs that have been built to date.61
As with other fast reactors, SFRs could use a closed fuel cycle in which plutonium and uranium
would be re-used from the spent fuel to provide a long-term fuel source when configured as a
breeder. SFRs can achieve high burnup of actinides in spent fuel, potentially reducing the longterm radioactivity of high-level nuclear waste.
The first SFR was built in the United States in 1951.62 Since then, approximately 20 SFRs have
been built around the world, most of which have been experimental. The United States
maintained SFRs as a high priority focus of its nuclear R&D program (primarily due to the
technology’s plutonium breeding capabilities) up until the cancellation of the Clinch River
Breeder Reactor demonstration plant in 1983 amid public opposition, rising construction costs,
and increased concern over weapons proliferation.63 There are five SFRs currently in operation
worldwide: one in China, three in Russia, and one in India. Two others are currently under
construction and several others are planned.64
DOE announced a 50% cost-shared ARDP award to TerraPower in October 2020, with federal
funding of up to $2 billion, for an SFR demonstration plant in Wyoming to begin operation by
2030. TerraPower’s Natrium plant uses an SFR designed by GE Hitachi (called PRISM) in
conjunction with a molten-salt heat storage system that would allow variable electrical output as
high as 500 MW. According to TerraPower, the Natrium reactor will use HALEU fuel rather than
plutonium. Spent fuel from the reactor will not be reprocessed to separate plutonium and uranium
for new fuel, according to the company, but long fuel burnup and high energy efficiency will
“reduce the volume of waste per megawatt hour of energy produced at the back end of the fuel
cycle, by five times.”65 GE Hitachi’s PRISM design was selected as the basis for the design
61 Cochran et al., “Fast Breeder Reactor Programs: History and Status.” For more information on the fire risk presented
by liquid sodium coolants, see Tara Jean Olivier et al., “Metal Fire Implications for Advanced Reactors, Part 1:
Literature Review,” Sandia National Laboratories, October 1, 2007, https://doi.org/10.2172/946583. For a description
of past SFR accidents, see Union of Concerned Scientists, “A Brief History of Nuclear Accidents Worldwide,”
https://www.ucsusa.org/nuclear-power/nuclear-power-accidents/history-nuclear-accidents#.XA7fV2N7mUk.
62 Experimental Breeder Reactor I (EBR-I), a 1.2 MWt sodium-cooled experimental fast reactor, was built in 1951 in
Idaho and produced both plutonium and electrical power. For a brief history of the reactor, see Rick Michal, “Fifty
Years Ago in December: Atomic Reactor EBR-1 Produced First Electricity,” Nuclear News, November 2001,
https://www.ne.anl.gov/About/reactors/ebr1/2001-11-2.pdf.
63 R&D activities related to SFRs and spent fuel reprocessing continued after 1983. For more on the history of the U.S.
program on liquid metal fast breeder reactors, see Cochran et al., “Fast Breeder Reactor Programs: History and Status,”
See also U.S. Atomic Energy Commission, Division of Reactor Development and Technology, “Liquid Metal Fast
Breeder Reactor Program Plan,” Vol. 1 (1968).
64 World Nuclear Association, “Fast Neutron Reactors,” August 2021, http://www.world-nuclear.org/informationlibrary/current-and-future-generation/fast-neutron-reactors.aspx.
65 TerraPower, “The Natrium Program,” May 18, 2021, https://www.terrapower.com/natrium-program-summary;
Government Accountability Office, Nuclear Energy Projects: DOE Should Institutionalize Oversight Plans for
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ofDOE’s planned Versatile Test Reactor at INL, although the project has not received new
appropriations since FY2021.66
ARC Clean Technology is developing a 100 MWe SFR based on the now-closed Experimental
Breeder Reactor II at INL.67 DOE awarded the company $27.5 million over three years in
December 2020 to develop a conceptual design.68
Demonstrations of New Reactor Types, GAO-22-105394, September 2022, p. 9, https://www.gao.gov/assets/gao-22105394.pdf.
66 DOE Office of Nuclear Energy, Draft Versatile Test Reactor Environmental Impact Statement Summary, DOE/EIS0542, December 2020.
67 ARC Clean Technology, https://www.arc-cleantech.com.
68 DOE, “Energy Department’s Advanced Reactor Demonstration Program Awards $20 million for Advanced Reactor
Concepts,” December 22, 2020, https://www.energy.gov/ne/articles/energy-departments-advanced-reactordemonstration-program-awards-20-million-advanced.
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Figure 4. Pool-Type and Loop-Type Sodium-Cooled Fast Reactors
Source: U.S. Department of Energy, modified by CRS.
Lead-Cooled Fast Reactor
Lead-cooled fast reactors (LFRs) are designed to use a closed fuel cycle with either molten lead
or lead-bismuth eutectic (LBE) alloy as a primary reactor coolant (see Figure 5).69 The use of
69 “The eutectic mixture is the specific composition of at least two solid components that produces a change of phase to
liquid at a certain temperature.” ScienceDirect, “Eutectic Mixture,” https://www.sciencedirect.com/topics/chemistry/
eutectic-mixture.
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lead as a coolant is seen to confer several advantages. As with the SFR, the use of a liquid metal
coolant allows for low-pressure operation and passive cooling in an accident. In contrast to liquid
sodium, however, molten lead is relatively inert, adding additional safety and economic
advantages. Lead also has a high rate of retention of radioactive fission products, which could
reduce accidental releases of radioactive materials to the environment. LFRs can also be designed
for high burnup of waste actinides, allowing for reduced long-term radioactive wastes.
Lead does present some challenges that may require further research and innovation to overcome.
At high temperatures, lead tends to corrode structural steel. Achieving commercialization for
designs in the higher temperature ranges would thus need further technological advances in
corrosion-resistance for structural steel components coming into contact with the liquid lead
coolant. Lead is also highly opaque, presenting visibility and monitoring challenges within the
core, and very heavy, due to its high density. The high melting point of lead also presents
challenges in terms of keeping the lead in liquid form so that it can continue to circulate under
lower-temperature scenarios.70
Russia is the world leader in LFR R&D, with experience building and operating seven LFRs for
use in submarines. Russia is building a lead-cooled demonstration fast reactor, the BREST-300
(300 MWe), in Seversk, with larger units to follow if the first is successful.71 Members of the
European Union have also announced a collaboration to develop an LFR through the Advanced
Lead Fast Reactor European Demonstrator (Alfred).72 Other countries exploring LFR
technologies include China, Japan, Korea, Sweden, and the United Kingdom. U.S. companies
pursuing LFRs include Westinghouse.73
70 Generation IV International Forum, “Lead-Cooled Fast Reactor (LFR),” 2019, https://www.gen-4.org/gif/jcms/
c_42149/lead-cooled-fast-reactor-lfr.
71 World Nuclear Association, “Nuclear Power in Russia,” December 2021, http://www.world-nuclear.org/informationlibrary/country-profiles/countries-o-s/russia-nuclear-power.aspx; “Russian Reactions,” Nuclear Engineering
International, May 22, 2016, https://www.neimagazine.com/features/featurerussian-reactions-4899799/.
72 “Ansaldo Nucleare Signs Contract for Lead-Cooled Reactor,” Nuclear Engineering International, November 25,
2021, https://www.neimagazine.com/news/newsansaldo-nucleare-signs-contract-for-lead-cooled-reactor-9277875.
73 Westinghouse, “Lead-cooled Fast Reactor (LFR): The Next Generation of Nuclear Technology,” viewed November
14, 2022, https://www.westinghousenuclear.com/energy-systems/lead-cooled-fast-reactor.
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Figure 5. Lead-Cooled Fast Reactor
Source: U.S. Department of Energy, modified by CRS.
Molten Salt Reactors and Fluoride Salt-Cooled High Temperature Reactors
Any reactor that uses molten salts as a coolant or fuel may be considered a molten salt reactor
(MSR). Salt-cooled MSRs (also known as fluoride salt-cooled high temperature reactors or
FHRs) employ molten salts to cool the core, which is composed of solid fuel blocks configured
much like an HTGR. Salt-fueled MSRs, by contrast, are unique in that the fuel is not solid, but
rather is dissolved in the molten salt coolant.74
MSRs vary in their design; there are fast and thermal variants, and different moderator materials
have been proposed for the thermal variants. Molten salt fast reactors (MSFRs) exhibit high
potential for waste actinide burnup and fuel resource conservation. Different molten salts may
also be used, depending on the other design features. Outlet temperature specifications range
from 700°-1,000°C, although there are challenges to operating at these temperatures that would
need technological advances to resolve. Despite the high temperatures, MSRs would operate at
low pressure and would not explosively react with air or water. It is unknown whether spent MSR
74 Oak Ridge National Laboratory, “Fluoride-Salt-Cooled High-Temperature Reactors,” January 30, 2018,
https://www.ornl.gov/content/fluoride-salt-cooled-high-temperature-reactors.
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fuel could be safely stored in the long term without undergoing additional treatment after removal
from the reactor.75
Unique to MSR salt-fueled designs is a safety feature called a “freeze plug” below the reactor
core, consisting of a salt plug that is cooled to a solid state (see Figure 6). If an incident caused
heat to rise in the core, the plug would melt, allowing the molten salt fuel to drain by gravity into
a basin designed to prevent the fuel from undergoing further fission reactions and overheating.
In theory, molten salt-fueled reactors could have on-line refueling, as well as on-line removal of
fission products and other impurities through a variety of potential processes. Such on-line fuel
processing could pose challenges for nuclear material inventory tracking for nonproliferation
purposes.76
MSR technology has been under development for decades. Two thermal-spectrum experimental
reactors were built in the United States at Oak Ridge National Laboratory in the 1950s and 1960s.
The first molten salt fuel irradiation tests since the completion of those early experiments were
conducted in 2017 in the Netherlands, where research on waste treatment is also being pursued.77
China is currently developing two prototype MSR microreactors with expected start dates in the
2020s.78
Terrestrial Energy, a Canadian company with a U.S. subsidiary, is in the second stage of design
review with the Canadian Nuclear Safety Commission for its integral molten salt reactor (IMSR).
The IMSR is the first advanced reactor design to complete phase one of the Canadian prelicensing process.79 The company’s U.S. subsidiary is conducting pre-application activities for the
IMSR with NRC.80 Terrestrial Energy has announced a goal of commercialization by the late
2020s.
Kairos Power received a 50% cost-shared ARDP risk reduction grant for its molten salt cooled
reactor technology in December 2020, with total federal funding of up to $303 million over seven
years.81 Kairos submitted a construction permit application to NRC in September 2021 to build a
75 Uranium tetrafluoride—the primarily fuel form for MSRs—reacts with water to form a highly corrosive acid which
can cause storage containers to degrade and fail prematurely. Lindsay Krall and Allison Macfarlane, “Burning Waste or
Playing with Fire? Waste Management Considerations for Non-Traditional Reactors,” Bulletin of the Atomic Scientists
74, no. 5 (September 3, 2018): 326-34, https://doi.org/10.1080/00963402.2018.1507791.
76 NASEM, Potential Merits and Viability of Advanced Nuclear Reactors and Associated Fuel Cycles, p. 67. Most
reactors, both existing and proposed, require periodic shutdowns for refueling. Canadian-designed CANDU reactors
provide an existing example of on-line refueling.
77 NRG, “MSR Irradiation Program at NRG Petten,” presentation by P.R. Hania to MSR Workshop 2018, Oak Ridge
National Laboratory, October 4, 2018, https://msrworkshop.ornl.gov/wp-content/uploads/2018/10/MSR2018presentation-Hania-NRGEU.pdf.
78 World Nuclear Association, “Molten Salt Reactors,” May 2021, http://www.world-nuclear.org/information-library/
current-and-future-generation/molten-salt-reactors.aspx.
79 “IMSR Starts Second Stage of Canadian Design Review,” World Nuclear News, October 17, 2018,
http://www.world-nuclear-news.org/Articles/IMSR-starts-second-stage-of-Canadian-design-review; and “Terrestrial
Energy Completes Safeguards Work at Canadian Nuclear Laboratories,” press release, August 31, 2022,
https://www.terrestrialenergy.com/2022/08/31/terrestrial-energy-completes-safeguards-work-at-canadian-nuclearlaboratories.
80 NRC, “Integral Molten Salt Reactor (IMSR),” May 31, 2022, https://www.nrc.gov/reactors/new-reactors/advanced/
licensing-activities/pre-application-activities/imsr.html.
81 DOE, “Energy Department’s Advanced Reactor Demonstration Program Awards $30 Million in Initial Funding for
Risk Reduction Projects,” December 16, 2020, https://www.energy.gov/ne/articles/energy-departments-advancedreactor-demonstration-program-awards-30-million-initial.
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35 MW (thermal) test reactor called Hermes at Oak Ridge, TN, supported by the ARDP grant.82
The Kairos technology consists of pebble bed TRISO fuel cooled by cooled by liquid fluoride
salt. The commercial version of the reactor, which is undergoing NRC pre-application activities,
would have a capacity of 145 MW(e).83
Examples of other U.S. companies developing MSRs include Alpha Tech Research Corp.,
Elysium Industries, Flibe Energy, Micronuclear, and TerraPower.84
Figure 6. Molten Salt Fueled Reactor
Source: U.S. Department of Energy, modified by CRS.
Fusion Reactors
Fusion reactors would fuse light atomic nuclei—as opposed to the fissioning of heavy nuclei—to
produce power. Fusion R&D has received significant federal investment over time, including
billions of dollars in international cooperative funding anticipated to build the International
82 NRC, “Hermes—Kairos Application,” November 14, 2022, https://www.nrc.gov/reactors/non-power/hermes-
kairos.html.
83 Kairos Power, “How It Works,” https://kairospower.com/technology; NRC, “Kairos,” August 21, 2022,
https://www.nrc.gov/reactors/new-reactors/advanced/licensing-activities/pre-application-activities/kairos.html.
84 World Nuclear Association, “Molten Salt Reactor,” May 2021, https://world-nuclear.org/information-library/currentand-future-generation/molten-salt-reactors.aspx; and DOE, Gateway for Accelerated Innovation in Nuclear, Advanced
Nuclear Directory, June 2021, https://gain.inl.gov/SiteAssets/Advanced%20Nuclear%20Directory/Archive/
GAINAdvancedNuclearDirectory-SeventhEdition_07.01.2021.pdf.
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Thermonuclear Experimental Reactor (ITER), a fusion research and demonstration reactor under
construction in France. The United States is a major participant in the project.
Fusion power would require light atoms, generally isotopes of hydrogen, to be heated to 100
million degrees Celsius to form a plasma, a state of matter in which electrons are stripped away
from the atomic nucleus. Holding the plasma together while it is heated sufficiently to create a
sustained fusion reaction is a major technical challenge. ITER would do this with a powerful
magnetic field (magnetic confinement fusion), while other approaches would compress a pellet of
hydrogen with lasers or other intense energy sources (inertial confinement fusion). Fusion
reactions are routinely produced at the laboratory scale. A key goal of ITER is to achieve
“burning plasma,” in which the plasma is heated mostly by its own fusion reactions rather than by
external energy sources. A fusion power reactor would need to go beyond this to achieve
“ignition,” in which the fusion energy exceeds the external energy input, allowing the fusion
reaction to be self-sustaining. ITER had been scheduled to produce its first plasma by the end of
2025, with full operations, including burning plasma experiments, scheduled to begin in 2035.85
However, the need for “extensive repairs” in key installed components will delay that schedule,
the project’s director announced in November 2022.86
DOE announced two milestones in the development of inertial confinement fusion in 2022. In
January, the National Ignition Facility at Lawrence Livermore National Laboratory achieved a
burning plasma, and in December the same facility achieved ignition. During the December
announcement, Livermore Lab Director Kimberly S. Budil said commercialization of the
technology would still take “a few decades,” but was “moving to the foreground.”87 The primary
purpose of the National Ignition Facility is to provide data for stewardship of the nation’s nuclear
weapons stockpile. Most researchers continue to see magnetic confinement fusion as the more
promising option for energy applications.88
Fusion power technology potentially has several safety and waste advantages over fission power
plants. Fusion reactions do not produce the intensely hot and radioactive spent fuel that results
from the fission process. If a fusion reactor shuts down, there is no radioactive core that must
continue to be cooled as in a fission reactor. According to the Fusion Industry Association,
“fusion produces no harmful emissions or waste fuel. A fusion power plant is physically
incapable of having a meltdown. There is no fissile radioactive waste left over.”89 However, some
reactor materials would be made radioactive by neutron exposure during a fusion reaction, and
tritium, a primary anticipated fuel source, is radioactive, although far less so than fission
products.90
85 ITER, “Building ITER,” September 30, 2022, https://www.iter.org/construction/construction. This timeline is
according to the project’s 2016 baseline schedule, but an update is currently underway. ITER construction was 77.5%
complete toward production of first plasma as of September 30, 2022, according to the project website.
86 “ITER Project Addressing Challenges,” ITER press release, November 17, 2022, https://www.iter.org/doc/www/
content/com/Lists/list_items/Attachments/1061/2022_11_IC-31.pdf.
87 Ben Lefebvre, “America Has Achieved a Tremendous Scientific Breakthrough,” Politico, December 13, 2022,
https://www.politico.com/news/2022/12/13/fusion-breakthrough-doe-energy-sustainability-00073666; DOE, “DOE
National Laboratory Makes History by Achieving Fusion Ignition,” December 13, 2022, https://www.energy.gov/
articles/doe-national-laboratory-makes-history-achieving-fusion-ignition.
88 For example, the advocacy group U.S. Fusion Energy describes magnetic confinement fusion as “the leading global
approach.” See U.S. Fusion Energy, “Approaches to Fusion,” https://www.fusionindustryassociation.org/fusionenergy.
89 Fusion Industry Association, “About Fusion,” April 12, 2019, https://www.fusionindustryassociation.org/
fusionenergy.
90 Paul Humrickhouse, Idaho National Laboratory, “Safety Considerations of Building a Fusion Pilot Plant,” June 23,
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Examples of U.S. companies developing fusion technologies include Commonwealth Fusion
Systems,91 Helion Energy,92 HyperV Technologies,93 Lawrenceville Plasma Physics,94 Lockheed
Martin, Magneto,-Inertial Fusion Technologies,95 and TAE Technologies.96
Major Criteria for Evaluating Unconventional
Technologies
With dozens of advanced nuclear technology developers vying for commercialization of their
concepts—as well as for federal support toward achieving that goal—several major criteria are
likely to help determine which reactor designs, if any, ultimately succeed. These include cost and
economic competitiveness, safety, weapons proliferation risk and security, versatility in size and
use, waste management, and other environmental effects. Cost and market viability are heavily
weighted criteria for ARDP demonstrations, along with technical feasibility and ability to meet
NRC safety and licensing requirements. Advanced reactor developers contend that their designs
offer major improvements in many or all of these criteria over existing conventional reactors,
although some critics have expressed skepticism.97
Cost
Investment in electricity generating technologies is largely determined on the basis of cost.
Nuclear energy has historically had high capital costs,98 but relatively low fuel and other
production costs. Conventional nuclear power plants have struggled to compete with natural gas
and renewable energy plants, particularly in regions of the country served by competitive
electricity markets. The success of advanced reactors in entering these markets may depend on
their ability to reduce capital costs relative to conventional reactors and to offer electricity prices
that are competitive with non-nuclear sources of baseload power. Government mandates and
subsidies for low-carbon generating technologies could help overcome cost differentials with
fossil fuel plants.
Commercial scale demonstration plants could help with the development of realistic cost
estimates. As noted by NASEM in its December 2022 report, “Because of the absence of current
commercial operational experience with advanced reactor technologies in the United States,
reliable cost data and estimates for these technologies and their associated fuel cycle components
2020, https://suli.pppl.gov/2020/course/SULI_Safety_2020-06-23.pdf.
91 Commonwealth Fusion Systems, https://cfs.energy.
92 Helion Energy, https://www.helionenergy.com.
93 HyperV Technologies, http://hyperv.com.
94 LPP Fusion, https://www.lppfusion.com.
95 Magneto-Inertial Fusion Technologies, https://miftec.com.
96 TAE Technologies, https://tae.com.
97 For example, see Edwin Lyman, ‘Advanced’ Isn’t Always Better: Assessing the Safety, Security, and Environmental
Impacts of Non-Light-Water Reactors, Union of Concerned Scientists, March 18, 2021, https://www.ucsusa.org/
resources/advanced-isnt-always-better.
98 EIA defines capital cost as “the cost of field development and plant construction and the equipment required for
industry operations.” See EIA, “Glossary,” EIA, November 9, 2018, https://www.eia.gov/tools/glossary/.
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are lacking.” NASEM recommended that DOE obtain independent expert cost estimates for
commercial deployment of advanced reactor technologies.99
Capital Costs
High capital costs present a significant barrier to deployment of new nuclear plants in the United
States. Conventional nuclear reactors are more expensive to build than most other power
plants.100 Nuclear plants must submit to much more rigorous safety regulation and quality
standards than other producers of electricity because of the risk posed by a release of radioactive
materials. As a result, they require highly specialized construction materials (e.g., nuclear-grade
steel), engineering knowledge, and construction expertise, all of which add to a plant’s costs.
Large conventional reactors require a great deal of on-site fabrication of structures and
components that are too large to be built in a factory, further adding to costs. High capital costs
and consequent financing needs make nuclear power plant construction especially vulnerable to
rising interest rates.
Capital cost estimates for advanced reactors vary by technology and design. Some designs, such
as SMRs, may allow for greater factory fabrication than conventional designs. Costs will remain
highly uncertain until demonstration plants are constructed. According to an MIT study,
conventional nuclear capital costs are dominated by labor and engineering costs (approximately
60%).101 By contrast, the actual reactor and associated turbine components comprise less than
20% of the capital cost of the median historical U.S. light water reactor.102 Accordingly, achieving
cost reductions relative to these conventional plants would require that advanced reactor
developers find ways to improve upon existing construction methods for nuclear reactors.
One advanced reactor design innovation that holds potential for reducing construction costs is
modularization of structures and components. Modularity is intended to increase factory
production of nuclear components. Manufactured components could then be delivered to the
construction site for installation, cutting down on onsite labor, reducing the specialized
knowledge needed to custom-build each component on-site, and potentially improving quality.
Modularized construction has been shown to improve the pace of construction and reduce costs in
other industries, as well as in some recent nuclear construction projects in Asia.103 NuScale, a
U.S.-based SMR vendor, has estimated “overnight” (excluding interest incurred during
construction)104 cost savings of approximately 10% due to modular construction of structures in
its proposed SMR plant. The Westinghouse AP1000 design, based on existing large conventional
reactors, is also intended to maximize modular construction, but the two AP1000 units under
99 National Academies of Sciences, Engineering, and Medicine, Merits and Viability of Different Nuclear Fuel Cycles
and Technology Options and the Waste Aspects of Advanced Nuclear Reactors, December 2022, p. 9,
https://nap.nationalacademies.org/catalog/26500/merits-and-viability-of-different-nuclear-fuel-cycles-and-technologyoptions-and-the-waste-aspects-of-advanced-nuclear-reactors.
100 Lazard, “Lazard’s Levelized Cost of Energy Analysis—Version 15.0,” October 2021, p. 11,
https://www.lazard.com/media/451881/lazards-levelized-cost-of-energy-version-150-vf.pdf.
101 A particularly large component of these costs comes from civil works required to prepare a site to host a nuclear
reactor. These include “excavations and foundations, the ultimate heat sink (cooling towers or river cooling), other
equipment, and the installation of plant components.” Massachusetts Institute of Technology, “The Future of Nuclear
Energy in a Carbon-Constrained World.”
102 Ibid.
103 Ibid., pp. 44-45.
104 “Overnight cost” is a method of comparing construction costs that assumes a plant could be built instantly, or
“overnight,” thus eliminating financing costs incurred during construction.
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construction at the Vogtle plant in Georgia have experienced long schedule delays and cost
overruns.
Advanced reactor developers and advocates have also highlighted the cost reduction potential of
such characteristics as simplified reactor designs, standardized reactor components, and smaller
overall reactor sizes. Designs using TRISO fuel contend that conventional containment structures
will not be needed because the multiple fuel coatings serve as a “functional containment.”105
Advanced reactors may also offer the potential to reduce financing costs as a result of shorter
construction times and, in the case of SMRs, the ability to begin generating revenue after the
installation of the first module, even as work continues on additional modules.
Operating Costs
Some advanced reactor concepts also show potential for reducing operating costs. Some designs
would utilize simpler systems or increased automation to reduce human labor costs during
operation. Many advanced reactor developers contend their designs would improve upon the
thermal efficiencies of older generations of nuclear plants by operating at higher temperatures or
through use of more efficient power conversion technologies. More-efficient plants may be able
to reduce their payback periods relative to their less efficient peers.
Not all aspects of advanced reactor concepts would lead to cost reductions. Some reactor designs
would have lower power ratings and/or lower power densities (less power for a given core
volume) than conventional reactors, which could reduce the cost advantages that existing large
reactors achieve through economies of scale. The majority of advanced designs would require
fuels with a fissile isotope enrichment of between 5% and 20% (HALEU), compared with 3%-5%
for most existing commercial reactors. Enriching fuel to these higher percentages would add
costs. Some designs would use as-yet-unlicensed fuel forms, which may be associated with
higher fuel fabrication costs. Some advanced reactors would also require spent fuel reprocessing
and treatment on the back end before wastes could be safely stored, which may in turn require
higher levels of security in order to limit risks of proliferation. According to NASEM,
“Reprocessing will likely be a costly addition to the fuel cycle, and notably, a single reprocessing
technology will not support the wide array of advanced reactor designs.”106
Some research on SMRs has suggested that their small size will prevent them from achieving
economies of scale. Modularization may allow this disadvantage to be balanced by so-called
“economies of multiples.” One analysis found that, while SMRs may be cheaper than traditional
reactors to construct, the cost per unit of power generated is likely to be higher.107
105 “The term ‘functional containment’ is applicable to advanced non-LWRs without a pressure retaining containment
structure. A functional containment can be defined as ‘a barrier, or set of barriers taken together, that effectively limit
the physical transport and release of radionuclides to the environment across a full range of normal operating
conditions, AOOs [anticipated operational occurrences], and accident conditions.’” X-energy, TRISO-X Pebble Fuel
Qualification Methodology, p. 36, https://www.nrc.gov/docs/ML2124/ML21246A289.pdf.
106 National Academies of Sciences, Engineering, and Medicine, Merits and Viability of Different Nuclear Fuel Cycles
and Technology Options and the Waste Aspects of Advanced Nuclear Reactors, December 2022, p. 138,
https://nap.nationalacademies.org/catalog/26500/merits-and-viability-of-different-nuclear-fuel-cycles-and-technologyoptions-and-the-waste-aspects-of-advanced-nuclear-reactors.
107 M. Granger Morgan et al., “US Nuclear Power: The Vanishing Low-Carbon Wedge,” Proceedings of the National
Academy of Sciences 115, no. 28 (July 10, 2018): 7184–89, https://doi.org/10.1073/pnas.1804655115.
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Cost Estimates for Advanced Reactors
It is difficult to accurately estimate the costs of advanced reactors. Many advanced reactor
concepts remain in the early stages of design and development, and vendor companies generally
do not include detailed costs in their publicly available content. Academic analyses of the costs of
non-traditional reactors have produced a range of results. The potential cost of fuel cycle facilities
raises additional uncertainty. For example, reactors that would use new types of fuel may need
new fuel fabrication plants, and technologies based on a closed fuel cycle would require spent
fuel reprocessing plants.
A common metric for measuring and comparing the cost of electricity production among sources
is the levelized cost of electricity (LCOE). LCOE is a measure of the unit cost of producing
electricity from a given generating source (e.g., coal, natural gas, solar, wind, etc.) and is
calculated by dividing the total costs of constructing and operating a plant over its lifetime by its
total electricity output over the same period. LCOE can be a useful tool for comparing production
costs across sources; however, because there are additional factors that influence the economic
competitiveness of a proposed plant, relying upon a single metric for comparison may be
misleading. Other possible cost measures include the cost of construction per kilowatt or
megawatt of electric generating capacity and the costs of air emissions. Such estimates typically
exclude costs that are not currently the responsibility of plant owners, such as greenhouse gas
emissions.
The Energy Information Administration (EIA) estimates that the LCOE for new nuclear reactors
is $88.24/MWh, excluding tax credits.108 An LCOE analysis by Lazard estimates that new nuclear
plants, unsubsidized and excluding decommissioning costs, would range from $151/MWh to
$196/MWh.109 Both are based on new plants using the most advanced currently available
technology. A comparison of levelized cost estimates for new nuclear plants and other new
generating capacity is shown in Table 3. Recent inflation could increase the uncertainty of such
estimates, however. For example, NuScale announced in November 2022 that the LCOE of its
planned first plant at INL had risen from $58/MWh to nearly $90/MWh, including federal
subsidies. The increases were attributed to rising supply and financing costs.110 A recent analysis
estimates that those costs would be above $100/MWh without DOE subsidies and the tax credits
in the Inflation Reduction Act.111 The overnight cost of the NuScale plant at INL is currently
estimated at $6.8 billion before federal subsidies.112
108 EIA, Levelized Costs of New Generation Resources in the Annual Energy Outlook 2022, March 2022,
https://www.eia.gov/outlooks/aeo/pdf/electricity_generation.pdf.
109 Lazard, Lazard’s Levelized Cost of Energy Analysis—Version 15.0, October 2021, https://www.lazard.com/media/
451905/lazards-levelized-cost-of-energy-version-150-vf.pdf.
110 Jeff Beattie, “NuScale Says Costs of SMR Plant in Idaho Have Climbed Due to Inflation, Nucleonics Week,
November 23, 2022. A description of federal funding for the nuclear energy industry is provided by Taxpayers for
Common Sense, Doubling Down: Taxpayers’ Losing Bet on NuScale and Small Modular Reactors, December 2021,
https://www.taxpayer.net/wp-content/uploads/2021/12/TCS_Doubling-Down-SMR-Report_Dec.-2021.pdf.
111 David Schlissel, Institute for Energy Economics and Financial Analysis, Small Modular Reactor Update: The
Fading Promise of Low-Cost Power from UAMPS’ SMR, November 17, 2022, https://ieefa.org/resources/smallmodular-reactor-update-fading-promise-low-cost-power-uamps-smr.
112 Michael McAuliffe, “NuScale Extends Cost Guarantees to Owners of First US SMR Plant,” Nucleonics Week,
January 18, 2023, p. 1.
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Table 3. Levelized Cost of Energy (LCOE) Estimates for New Power Plants Using
Selected Technologies
($ per megawatt-hour, excluding federal subsidies)
Energy Source
EIA
Lazard
Notes
Nuclear
88
131-204
Advanced large LWRs, currently available technology
Coal
83
65-152
Ultra-supercritical; Lazard high estimate includes carbon capture
Natural gas
40
45-74
Combined cycle
Geothermal
40
56-93
Hydrothermal
Biomass
90
Wind, onshore
40
26-50
Wind, offshore
137
83
Solar
36
30-41
Utility-scale photovoltaic
Sources: EIA, Levelized Costs of New Generation Resources in the Annual Energy Outlook 2022, March 2022,
https://www.eia.gov/outlooks/aeo/pdf/electricity_generation.pdf; Lazard, Lazard’s Levelized Cost of Energy
Analysis—Version 15.0, October 2021, https://www.lazard.com/media/451905/lazards-levelized-cost-of-energyversion-150-vf.pdf.
Size
Advanced reactor designs come in a wide range of sizes, from less than 15 MWe to 1,500 MWe
or more. In some cases, the optimal reactor size may be influenced by the particular
characteristics of a given design. In others, the size may be determined by the needs of the
customer or site.
A commonality among many unconventional reactor concepts is an increased focus on small
reactor designs. As noted earlier, advanced SMRs, 300 MWe and below, “employ modular
construction techniques, ship major components from factory fabrication locations to the plant
site by rail or truck, and include designs that simplify plant site activities required for plant
assembly,” according to DOE.113 The smallest of these—under 20 MW of thermal energy—may
also be referred to as microreactors. As noted above, most existing conventional reactors in the
United States have an electrical generating capacity of 1,000 MWe or more. Many proposed
advanced reactor technologies, according to proponents, would have fundamental characteristics,
such as inherent safety, that would make them commercially viable at small sizes and not need
the economies of scale required by existing LWR technology.
The small size and modular nature of SMRs gives them the potential to expand the types of sites
and applications for which nuclear energy may be considered suitable (see section on
Versatility).114 SMR designs with multiple reactor modules may allow for size customization
based on the needs of the customer or characteristics of the host site. For example, SMRs may be
sized to directly replace retiring coal-fired power plants, as planned by the TerraPower Natrium
project in Wyoming. Small size may also make safety systems simpler and more reliable, as
discussed below.
113 DOE, “Advanced Small Modular Reactors (SMRs),” February 5, 2019, https://www.energy.gov/ne/nuclear-reactor-
technologies/small-modular-nuclear-reactors.
114 Small nuclear reactors are not a new concept. The U.S. military has built and used small nuclear reactor for dozens
of years, most notably to power submarines and large surface ships.
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According to NASEM,
Commercial viability will depend on understanding whether there is an optimal size for a
small modular reactor from an economic point of view and when the breakeven point will
be reached for the construction of an nth-of-a-kind reactor [in the middle of series
production] for a particular type of small modular reactor to become economically
competitive. In other words, the learning curve for both small modular reactor construction
costs and deployment needs to be understood.115
Safety
Safety with respect to nuclear energy refers primarily to the minimization of the risk of release of
radioactivity into the environment. Advanced reactor systems may have both safety advantages
and disadvantages in comparison with existing reactors as a result of their size and design, and
the chemical properties of their main components (e.g. the coolant, fuel, and moderator). Because
many of these technologies are in the design phase, the operational safety of many of these
systems has not yet been established in practice. Testing and demonstration would be needed to
fully validate the safety claims of advanced reactor vendors.
Conventional nuclear plants use multiple independent and redundant safety systems to minimize
risk. In the majority of cases, these systems are “active,” meaning that they rely on electricity or
mechanical systems to operate. Advanced nuclear reactors tend to incorporate passive and
inherent safety systems as opposed to active systems. Passive systems refer primarily to two types
of safety features: (1) the ability of these reactors to self-regulate the rate at which fission occurs
through negative feedback mechanisms that naturally reduce power output when certain system
parameters (such as temperature) are exceeded, and (2) the ability to provide sufficient cooling of
the core in the event of a loss of electricity or other active safety systems.116
The chemical properties of various advanced coolants, fuels, and moderators may also contribute
inherent safety advantages. Examples include higher boiling points for coolants, higher heat
capacities for fuels and moderators, and higher retention of radioactive fission products for some
coolants. Some advanced reactor coolants (such as liquid metals) remain at atmospheric pressure
under high reactor temperatures, putting less stress on primary reactor components than highpressure coolants such as water. Advanced reactors that can operate at or near atmospheric
pressure enable simplification of the coolant system design and safety systems, as well as the
potential for improved economic performance.
Proponents of small reactors have suggested that SMRs, and microreactors in particular, may
pose less of a safety risk due to the smaller total volume of radioactive material on site and lower
risk of release to the environment. Consequently, some have argued that they should face
streamlined approval processes in line with the NRC’s approach of risk-informed regulation.117
The smaller size of SMRs and microreactors may also enable innovations in siting that could
115 NASEM, Merits and Viability of Different Nuclear Fuel Cycles and Technology Options and the Waste Aspects of
Advanced Nuclear Reactors, p. 137.
116 Reactors that are designed such that the maximum temperature at equilibrium (when heat generation equals passive
heat removal) is below the point where fuel and reactor damage would occur are sometimes described by vendors as
being “walkaway safe.”
117 The NRC defines “risk-informed regulation” as “an approach to regulation taken by the NRC, which incorporates an
assessment of safety significance or relative risk,” and states that this approach “ensures that the regulatory burden
imposed by an individual regulation or process is appropriate to its importance in protecting the health and safety of the
public and the environment.” (NRC, “Risk-Informed Regulation,” March 9, 2021, https://www.nrc.gov/reading-rm/
basic-ref/glossary/risk-informed-regulation.html.)
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contribute to plant safety. Some have suggested that siting these reactors underground or on
floating platforms at sea could reduce risks related accidental release of radioactive materials and
seismic activity, respectively.118
While some advanced reactor coolants and moderators may have the advantages described above,
some also have chemical properties that pose safety concerns. Examples include reactivity,
toxicity, or corrosiveness of the primary coolant in the case of sodium, lead, and molten salts,
respectively. Molten salt-cooled reactors would incorporate the dissolved fuel into the coolant,
posing a safety concern for plant workers who must be shielded from the higher levels of
radioactivity flowing through the coolant system as a result. Opaque coolants present additional
challenges to visual core monitoring and inspection compared with transparent coolants like
water.
Advanced reactors, as well as some existing conventional reactors, may make use of advances in
fuel technologies and accident-tolerant fuels (ATFs). ATFs are designed to better withstand
overheating during an accident, reducing the risk of cladding oxidization and fuel meltdown and
allowing reactor operators more time to respond to accidents. Near-term ATF concepts (e.g.
coated zirconium cladding, iron-chrome-aluminum-based cladding) may be commercially
available as soon as the mid-2020s, while longer-term ATF concepts (e.g. metallic fuels, silicide
fuel, and silicon carbide cladding) would need more testing before they could be licensed.119
Advanced reactor technologies that would rely on spent fuel reprocessing and recycling, as well
as on HALEU fuel, could introduce safety concerns beyond those related to reactor operation.
Enrichment levels in HALEU, which are higher than in conventional fuel, would require added
measures to prevent accidental criticality (nuclear chain reactions) in fuel conversion, enrichment,
and fabrication facilities. Commercial reprocessing facilities, currently not operated in the United
States, would also require criticality controls, along with prevention of such industrial hazards as
fires, leaks, and chemical reactions that could spread radioactivity.120
Security and Weapons Proliferation Risk
In addition to producing energy for peaceful purposes, nuclear fuels such as uranium and
plutonium can be used by states to manufacture nuclear weapons material for military use or
diverted by non-state actors to produce weapons of mass destruction. The risk of weapons
proliferation from civilian nuclear materials and facilities presents a challenge for all nuclear
energy reactors to varying degrees, and for international controls on nuclear materials. Advanced
reactor designs may offer both advantages and disadvantages with respect to their potential
effects on nuclear weapons proliferation.
Advocates contend that many advanced reactor designs would be more resistant to weapons
proliferation than existing LWRs because of factors such as “sealed” or difficult-to-access core
designs, infrequent refueling, smaller inventories of fissile materials in the core, and remote
monitoring capabilities, among others. Some designs may produce waste that is less attractive for
weapons proliferation for a variety of reasons.121
118 World Nuclear Association, “Small Nuclear Power Reactors,” May 2022, http://www.world-nuclear.org/
information-library/nuclear-fuel-cycle/nuclear-power-reactors/small-nuclear-power-reactors.aspx.
119 NRC, “Accident Tolerant Fuel Regulatory Activities,” October 25, 2022, https://www.nrc.gov/reactors/atf.html.
120 NASEM, Merits and Viability of Different Nuclear Fuel Cycles of Advanced Nuclear Reactors, p. 140.
121 For a discussion of these advantages, as well as disadvantages, see Shikha Prasad et al., “Nonproliferation
Improvements and Challenges Presented by Small Modular Reactors,” Progress in Nuclear Energy, vol. 80 (April
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Advanced reactors may also present unique inspection and monitoring challenges. In a 2017
workshop report, IAEA, which inspects nuclear sites to ensure compliance with international
nonproliferation agreements, noted that some of the characteristics of advanced reactors may
make them more difficult to monitor and safeguard.122 For instance, the opacity of certain
advanced coolants, such as sodium, lead, and molten salts, may make it more difficult to monitor
reactor cores to ensure nuclear materials are not being diverted for weapons purposes. In contrast,
inspectors can visually see through cooling water to determine whether fuel rods and assemblies
are present or have been removed, possibly to separate plutonium for weapons.
The 2017 IAEA report identified several advanced reactor technologies that pose unique and
particularly difficult safeguarding challenges, including transportable reactors, pebble-bed design
HTGRs, molten salt reactors, and certain waste reprocessing facilities. The report also noted that
“proliferation resistance and ease to verify (safeguardability) are not interchangeable; and most of
the features lending proliferation resistance to Generation-IV reactors actually make safeguards
nuclear material accountancy more difficult.”123
The utilization by some advanced reactors of more highly enriched fuels could create additional
nonproliferation challenges. Many advanced designs would utilize HALEU, with a fissile isotope
enrichment of between 5% and 20%. At these higher enrichments, even very small reactors would
likely contain more than enough fissile material to produce multiple nuclear weapons with further
enrichment.124 The total work required to enrich uranium to weapons-grade levels declines as the
initial enrichment level rises.125 Some designs would also produce spent fuel with higher
concentrations of isotopes that are desirable from the point of view of weapons production,
making them a more attractive target of diversion than current LWR fuel. Additional security
measures may be necessary to safeguard against such eventualities.
The need to safeguard nuclear materials is present not just at reactor sites, but through the entire
nuclear fuel supply chain. This includes during uranium enrichment, the fuel fabrication process,
in transit, and, if applicable, during fuel reprocessing. Many advanced reactors would require or
would offer the option to reprocess the spent fuel to extract remaining fissile materials. Some
advanced reactor technologies would rely on reprocessing and recycling to make them costeffective. Separating these materials from the radioactive wastes makes them more attractive both
to thieves for making radiological dispersal devices and to countries that might use them to
produce weapons. France, Japan, India, Russia, and the United Kingdom have longstanding
civilian nuclear fuel programs. According to one independent estimate, about 545 metric tons of
separated plutonium was held around the world as of May 2022 in weapons or in stockpiles of
2015): 102–9, https://doi.org/10.1016/j.pnucene.2014.11.023.
122 IAEA, Emerging Technologies Workshop: Trends and Implications for Safeguards, February 2017,
https://www.iaea.org/sites/default/files/18/09/emerging-technologies-130217.pdf. Safeguards are defined by the IAEA
as “activities by which the IAEA can verify that a State is living up to its international commitments not to use nuclear
programmes for nuclear-weapons purposes.” (See https://www.iaea.org/publications/factsheets/iaea-safeguardsoverview.)
123 IAEA, Emerging Technologies Workshop. For more information about IAEA, see CRS Report RL33865, Arms
Control and Nonproliferation: A Catalog of Treaties and Agreements, by Paul K. Kerr and Mary Beth D. Nikitin.
124 Nuclear materials must generally reach fissile isotope enrichments of 90% or greater to be considered “weaponsgrade.” Accordingly, nuclear materials diverted from nuclear energy reactors at 5%-20% enrichment would require
further enrichment to reach this threshold. Plutonium in reactor fuel would not need enrichment to be useable for
weapons.
125 Prasad et al., “Nonproliferation Improvements and Challenges Presented by Small Modular Reactors.” See also
World Nuclear Association, “Uranium Enrichment,” October 2022, http://www.world-nuclear.org/information-library/
nuclear-fuel-cycle/conversion-enrichment-and-fabrication/uranium-enrichment.aspx.
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varying isotopic composition.126 For reference, the minimum fissile inventory required to produce
a nuclear weapon from plutonium is generally cited as 10 kg of Pu-239. This figure may vary
considerably based on the percentage of other plutonium isotopes mixed with Pu-239 and the
sophistication of weapons designs.127
For existing nuclear power plants in the United States, security and proliferation risks are
generally considered to be low, given the current fuel cycle and safeguards regimes in place. In
particular, the low-enriched uranium fuel (3%-5% U-235) in U.S. reactors cannot be used for a
nuclear explosive device without separation and further enrichment, and the United States does
not have commercial facilities for chemical separation of plutonium. Many observers view the
lack of reprocessing in the United States as a policy signal to other countries that the country with
the largest number of nuclear power plants in the world has been able to support this fleet without
reprocessing.
The 2022 NASEM study points out that IAEA has relatively little experience in safeguarding fast
reactors and pebble-bed reactors, and that “molten salt-fueled reactors are completely unexplored
territory for IAEA safeguards.” The report urges that the United States place all its advanced
reactors and fuel facilities under IAEA safeguards as soon as possible to help develop effective
safeguards methods for these technologies. “To the extent possible, these efforts would be
comprehensive and serve as models for full IAEA verification protocols in non-nuclear weapon
states where advanced reactors and fuel cycle facilities may be exported,” according to the
report.128
Versatility
Many advanced reactor designs are smaller than the existing fleet of LWRs and are designed for
modular installation of each generating unit. Because the number of modules may be altered to
meet the power and heating needs of the site, SMRs are intended to accommodate a range of sizes
and types of uses, including those that may have been considered too small in the past. SMRs and
microreactors have potential applications in providing power to remote and isolated areas, on-site
heating for industrial or municipal clients, and heat or power to mobile or temporary clients (e.g.
remote construction sites and temporary military stations). DOD has expressed interest in using
SMRs to power remote bases. As noted above, DOD announced in June 2022 that BWXT had
been selected to build the first advanced nuclear microreactor under “Project Pele.” The reactor is
to produce 1-5 MW and be operational by 2024.129 SMRs have also been described as potential
replacements for coal-fired generating units, which are generally far smaller than existing large
126 About 140 metric tons was estimated to be in nuclear weapons or available for weapons. International Panel on
Fissile Materials, “Fissile Material Stocks,” May 2, 2022, http://fissilematerials.org. For a description of national
civilian reprocessing programs, see Appendix H of National Academies of Sciences, Engineering, and Medicine,
Merits and Viability of Different Nuclear Fuel Cycles and Technology Options and the Waste Aspects of Advanced
Nuclear Reactors, December 2022, https://nap.nationalacademies.org/catalog/26500/merits-and-viability-of-differentnuclear-fuel-cycles-and-technology-options-and-the-waste-aspects-of-advanced-nuclear-reactors.
127 Weapons-grade plutonium has at least 94% Pu-239, although other grades are potentially useable for weapons.
Federation of American Scientists, “The Basics of Nuclear Weapons: Physics, Fuel Cycles, Effects and Arsenals,”
February 8, 2016, https://fas.org/wp-content/uploads/2014/05/Brief2016_CNP-MIIS_.pdf.
128 NASEM, Merits and Viability of Different Nuclear Fuel Cycles of Advanced Nuclear Reactors, p. 195.
129 BWX Technologies, “BWXT to Build First Advanced Microreactor in United States,” June 9, 2022,
https://www.businesswire.com/news/home/20220609005154/en/BWXT-to-Build-First-Advanced-Microreactor-inUnited-States.
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reactors.130 For example, the TerraPower Natrium demonstration plant in Wyoming is replacing a
closing coal-fired power plant that has units of similar size.
The 2018 MIT study cautioned that small size alone would not necessarily give advanced reactors
a market edge:
The industry’s problem is not that it has overlooked valuable market segments that need
smaller reactors. The problem is that even its optimally scaled reactors are too expensive
on a per-unit-power basis. A focus on serving the market segments that need smaller reactor
sizes will be of no use unless the smaller design first accomplishes the task of radically
reducing per-unit capital cost.131
Advanced reactors may also be designed for new applications or to capture new markets. Many
advanced nuclear reactors would operate at higher temperatures (500°-1,000°C) than existing
commercial LWRs (approximately 300°-330°C). Higher operating temperatures would allow
some advanced reactors to tap into the large market for heat for industrial processes. Some
advanced reactor designs, such as the Natrium plant, are being designed to rapidly change their
electrical output from stored heat to match utility demand (load following), such as in areas with
high percentages of highly variable wind and solar power.
Industrial users consume 25% of all primary energy produced in the United States, 80% of which
is in the form of process heat. MIT estimates that 17%-19% (or 134-151 GWt) of the U.S. market
for industrial heat could be supplied by small (150-300 MWt) advanced reactors.132 Potential
applications include providing heat for district heating,133 desalination, petroleum refining and oil
shale processing, cogeneration, biomass or coal gasification, and hydrogen production, among
others. Advanced reactors may nevertheless face steep barriers to entry into these markets in the
form of competition from other sources, such as natural gas plants (with or without carbon
capture and storage), that are perceived as being less risky, in both safety and economics.
Waste Management
The radioactivity of nuclear waste presents waste management and facility contamination
challenges that are unique to nuclear energy. Radioactivity builds up in a nuclear reactor in three
primary ways: 1) through the accumulation of radioactive “fission products” that result from the
splitting of fissile nuclei, 2) through the accumulation of radioactive “actinides” that form when
heavy atoms in the reactor core absorb a neutron but do not undergo fission, and 3) through the
generation of “activation products” in the coolant, moderator, or reactor components that occurs
when these materials are made radioactive by absorbing neutrons. The vast majority of the initial
radioactivity in nuclear waste comes from the fission products. Because of the long half-lives of
some of these radioactive materials, nuclear waste poses long-term health hazards.134
130 DOE, Investigating Benefits and Challenges of Converting Retiring Coal Plants into Nuclear Plants, INL/RPT-22-
67964, September 2022, https://fuelcycleoptions.inl.gov/SiteAssets/SitePages/Home/C2N2022Report.pdf.
131 Massachusetts Institute of Technology, “The Future of Nuclear Energy in a Carbon-Constrained World.”
132 The potential market for nuclear-supplied process heat could expand significantly if there were an increase in the
demand for hydrogen for fuel cell vehicles or biomass-based synthetic fuels. (Massachusetts Institute of Technology,
“The Future of Nuclear Energy in a Carbon-Constrained World.”)
133 Central heat for multiple buildings in a specified area.
134 NRC defines “half life” as the “time in which one half of the atoms of a particular radioactive substance disintegrate
into another nuclear form. Measured half-lives vary from millionths of a second to billions of years.” See NRC glossary
at https://www.nrc.gov/reading-rm/basic-ref/glossary/half-life.html.
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In 2022, the U.S. inventory of spent nuclear fuel from commercial reactors exceeded 90,000
metric tons of uranium (MTU) at 74 sites. This is projected to rise at an average rate of
approximately 1,800 MTU per year, based on the planned phaseout of the current reactor fleet,
resulting in an estimated 137,000 MTU by 2050.135 Because no long-term repository or
consolidated storage facility for high-level nuclear waste has been licensed by NRC, newly
discharged spent nuclear waste is currently stored onsite at nuclear plant locations.136
Unconventional reactors may offer some waste management advantages over existing
commercial reactors. Fast reactors, and some other unconventional reactors, would be more
effective at destroying actinides compared with commercial reactors. Actinides are responsible
for the vast majority of the radioactive hazard that remains in nuclear waste after the first few
centuries.137 Reducing the prevalence of these long-lived waste products by transmuting them to
short-lived radionuclides through reprocessing and recycling may reduce the health risk
associated with a release of spent fuel that occurs far in the future (when storage containers may
be more likely to fail).
In theory, by reducing the volume of this long-lived portion of the waste, smaller and fewer
permanent geological repositories would be required, and the separated short-lived waste could
be disposed of in landfills requiring stewardship for centuries rather than millennia. In practice,
the reprocessing-related liquid radioactive waste (generally nitric acid raffinate with mixed fission
products) have been technically difficult and expensive to manage. In the United States, where
recycling/reprocessing has occurred at four major sites, primarily for defense purposes, the
estimated environmental liability to stabilize, remediate, and provide stewardship is estimated at
hundreds of billions of dollars, requiring more than 75 years of active remedial efforts.
Proponents of advanced nuclear technologies contend that future reprocessing plants would
successfully treat waste for disposal as it is produced. However, it is unclear whether future
advanced reactor technologies would improve on past handling of reprocessing wastes as much as
proponents anticipate. As noted by the 2022 NASEM report, “The amounts and types of waste
that will be generated by advanced reactors are difficult to estimate at this early stage of the
development of advanced reactors; yet, this type of information is required in order to determine
the impact of advanced reactors and advanced fuel cycles on the back end of the fuel cycle.”138
Actinides are not the only long-lived nuclear wastes, however; some fission products remain
radioactive hazards for hundreds of thousands of years and longer. The presence of these fission
products in nuclear wastes might not be appreciably reduced by unconventional reactors. As a
result, some have argued that, even if advanced reactors are able to deliver the improvements in
135 Oak Ridge National Laboratory, “CURIE,” viewed November 28, 2022, https://curie.ornl.gov/map.
136 The Nuclear Waste Policy Act (P.L. 97-425) designates the Yucca Mountain site in Nevada as the sole candidate
site for a national repository, but no funds for licensing the Yucca Mountain repository have been appropriated since
FY2010. A 20-year license for a storage facility in Utah was issued by NRC in 2006, but the facility was never built.
NRC issued a license for a consolidated interim storage facility (CISF) in Texas on September 13, 2021, and is
considering a license application for a CISF in New Mexico. See the NRC news release on the Texas CISF license at
https://www.nrc.gov/reading-rm/doc-collections/news/2021/21-036.pdf. For more background, see CRS Report
RL33461, Civilian Nuclear Waste Disposal, by Mark Holt.
137 Radiactivity.eu.com, “Long-Lived Fission Products,” 2023, https://radioactivity.eu.com/nuclearenergy/
long_lived_fission_products.
138 NASEM, Management and Disposal of Nuclear Waste from Advanced Reactors, p. 164.
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actinide management that some advocates have claimed are possible, adoption of these reactors at
scale would not materially alter the need for a long-term waste repository.139
Some advanced reactors would use new or non-conventional fuel forms, such as metallic fuels,
dissolved molten fuels, or TRISO fuel. Some of these fuels pose additional waste management
challenges as a result of their tendency to corrode storage containers or otherwise react with the
environment in ways that complicate their safe storage and disposal. Gas-cooled reactors may
produce large volumes of radioactive graphite waste, while sodium-cooled fast reactor fuel may
require special treatment before safe disposal is possible. Fuel and coolant from molten salt
reactors may remain volatile even after solidification. Research on the safe management and
disposal of advanced reactor waste will be a key element in commercializing these
technologies.140
Environmental Effects
Environmental impacts for any electric power source must be evaluated based on air emissions,
water discharges, and waste management challenges, considering the full life cycle of the
technology. The recent focus for nuclear power environmental impacts has been on air emissions,
particularly its limited greenhouse gas footprint. Historically, however, much attention has been
given to the waste management challenges associated with nuclear power. The environmental
impacts of current LWR nuclear technologies are well studied. The stated goal of many advanced
reactor technologies is to reduce environmental impacts. The impacts for newer advanced
technologies would need to be evaluated on a case-by-case basis, and assessed empirically to
determine whether the impacts are greater or less than current technologies, and whether
advanced technologies eliminated any existing challenges in practice or raised new challenges
requiring new technologies, regulatory systems, and support industries.
Nuclear energy is a low-carbon source of electricity, with no direct emissions from the fission
process. As such, it is one of a number of energy technologies available for reducing the carbon
emissions associated with electricity production (and potentially other uses of energy, such as
industrial heat). The nuclear energy industry is not zero-carbon, however. Historically, fossil fuelpowered plants and equipment have provided energy to support the nuclear supply chain.
Uranium enrichment facilities, in particular, have high energy requirements, and U.S. enrichment
plants in the past used electricity primarily from coal-fired power plants. Current uranium
enrichment plants use only a fraction of the electricity of older enrichment technology and are
generally less reliant on coal-fired generation. A study by the DOE National Renewable Energy
Laboratory of the life-cycle greenhouse gas emissions of major electric generating technologies
found that conventional nuclear reactor emissions were similar to those of renewable energy
technologies and only a fraction of coal and natural gas plant emissions.141 Emissions of
conventional air pollutants (e.g., sulfur oxides, nitrogen oxides, mercury, and particulates) from
nuclear power operations and fuel cycle activities are similarly low.
Advanced reactors are expected to have similar life-cycle air emissions to those of existing
reactors. Supporters of advanced reactor technologies contend that they could reduce the
obstacles to nuclear power expansion related to cost, safety, waste management, and fuel supply
139 Krall and Macfarlane, “Burning Waste or Playing with Fire?”
140 NASEM, Management and Disposal of Nuclear Waste from Advanced Reactors, p. 164.
141 National Renewable Energy Laboratory, “Life Cycle Assessment Harmonization,” February 13, 2019,
https://www.nrel.gov/analysis/life-cycle-assessment.html.
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and therefore allow nuclear power to play a greatly expanded role in worldwide greenhouse gas
reduction strategies.
Some have argued that decarbonization goals could be achieved more effectively through
improvements in existing light water reactor technologies. In particular, such a strategy could
avoid additional waste management technical challenges and costs associated with the processing
of radioactive waste from some types of advanced reactors. This could include the near-term
management of potentially large volumes of low activity reprocessing waste.142 On the other
hand, as noted above, proponents of advanced reactor technologies contend that nuclear fuel
recycling/reprocessing could reduce the long-term radioactivity of nuclear waste and produce
waste forms more resistant to deterioration than LWR spent fuel.143
Plants with higher thermal efficiencies reject less heat into the environment per kilowatt-hour
(KWh) of electricity generated. This can help reduce ecosystem impacts related to heat rejection.
For example, increased efficiency may contribute to significant reductions in the amount of water
used for waste heat rejection (up to 50% less)144 per unit of electricity generated, and reduce the
amount of heat absorbed by adjacent water bodies. This could have particularly significant
implications for the use of nuclear energy in arid environments.
DOE Nuclear Energy Programs
The Department of Energy supports the development of advanced nuclear technologies through
research and development (R&D) programs housed in several DOE offices: particularly the
Office of Nuclear Energy, the Office of Science, and the Office of Clean Energy
Demonstrations.145 The Advanced Research Projects Agency—Energy (ARPA-E) also provides
funding for early stage R&D for advanced nuclear projects, and the National Nuclear Security
Administration (NNSA) funds inertial confinement fusion research primarily for defense
purposes. Collectively, nuclear R&D programs (including advanced fission and fusion) received
about 29% of funding for energy R&D in fiscal year (FY) 2023 (see Table 4).
142 Krall and Macfarlane, “Burning Waste or Playing with Fire?”
143 This issue is discussed in more detail at NASEM, Management and Disposal of Nuclear Waste from Advanced
Reactors, p. 164.
144 Massachusetts Institute of Technology, “The Future of Nuclear Energy in a Carbon-Constrained World.”
145 Activities related to the development of advanced nuclear technologies may also receive direct or indirect support
and funding from other DOE programs and accounts, including through budgets for facilities management,
environmental management, and others. This report focuses on funding provided for R&D through the congressional
appropriations process.
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Table 4. FY2023 Energy R&D Appropriations
$ in Millions
All Other Energy R&D
Renewables
Fossil
Nuclear
Energy Efficiency
and Vehicles
Electric
Systems
Demonstration
164
89
1,323
285
3,826
100
800
Fission
Regular
appropriations
792
890
1,687
Supplementals
300
1,444
110
Total
1,092
2,234
1,797
164
3,915
1,423
Percent
8%
17%
13%
1%
29%
10%
Class %
ARPA-E
68%
Reactor
Demonstration
29%
Fusion
Any Energy
Type
1,393
470
1,085
1,393
470
8%
10%
3%
3%
Source: Explanatory statement for Consolidated Appropriations Act, 2023; P.L. 117-58.
Notes: Includes appropriations for programs and activities related primarily to R&D. Fusion includes defense programs. Includes R&D-related FY2023 emergency
supplemental appropriations for DOE programs in the Infrastructure Investment and Jobs Act (P.L. 117-58) and additional FY2023 appropriations in P.L. 117-328 Division
M. Excludes FY2022 appropriations in P.L. 117-169 for DOE national laboratory infrastructure available through FY2027.
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Office of Nuclear Energy
The Office of Nuclear Energy (NE) “focuses on three major mission areas: the nation’s existing
nuclear fleet, the development of advanced nuclear reactor concepts, and fuel cycle
technologies,” according to DOE’s FY2023 budget justification.146 NE primarily supports nuclear
fission technologies at all stages of development, ranging from lab-scale experiments and
computer modeling to technology demonstration and support. Five advanced reactor
demonstration projects—two of which are to begin operating by around 2030—were initially
funded by NE and are transitioning to DOE’s Office of Clean Energy Demonstrations (OCED).
In FY2023, Congress appropriated $2.508 billion for DOE nuclear energy programs in NE and
OCED.147 These include the following:
Nuclear Energy Enabling Technologies: $96 million, includes crosscutting
technology development, modeling and simulation, and nuclear science user
facilities;
Fuel Cycle Research and Development: $422 million, includes HALEU fuel
availability, TRISO fuel qualification, and waste management R&D;
Reactor Concepts Research, Development, and Deployment: $259 million,
includes advanced SMR RD&D and advanced reactor technologies; and
Advanced Reactor Demonstration Program: $1.085 billion (including
supplemental appropriations), provides 50% cost sharing for two near-term
demonstration projects and 80% cost-sharing for three longer-term projects for
potential demonstration, as well as support for an advanced reactor licensing
framework and the National Reactor Innovation Center at INL.
To support private-sector nuclear energy innovation, DOE’s Gateway for Accelerated Innovation
in Nuclear (GAIN) initiative, begun in 2016, provides enhanced access to DOE’s network of
national labs and nuclear R&D capabilities, as well as through competitive industry funding
opportunities. A major industry funding mechanism under GAIN is the Nuclear Energy Voucher
Program, which provides industry awardees with access to DOE nuclear expertise and
capabilities in the form of vouchers redeemable for research and technical support activities at
one of DOE’s national laboratories. Recipients are required to provide a 20% minimum costshare.148
Office of Science
Support for fusion research is provided by the Fusion Energy Sciences (FES) program in DOE’s
Office of Science. FES focuses its research on magnetic confinement of plasmas (matter in which
electrons have been stripped away from atomic nuclei) to potentially create a “sustainable fusion
146 DOE, FY2023 Congressional Budget Justification, vol. 4, “Nuclear Energy,” March 2022, https://www.energy.gov/
sites/default/files/2022-04/doe-fy2023-budget-volume-4-ne.pdf.
147 Joint Explanatory Statement on the Consolidated Appropriations Act, 2023, Division D—Energy and Water
Development and Related Agencies Appropriations Act, 2023. Includes $300 million for the DOE Nuclear Energy
account in Division M—Additional Ukraine Supplemental Appropriations Act, 2023, and $600 million for ARDP in
IIJA. Excludes $150 million for Idaho sitewide security.
148 Not all Nuclear Energy Vouchers are awarded for advanced nuclear projects. Some projects are focused on
innovations to existing light water reactor technologies and related purposes. For more information, visit GAIN’s NE
Vouchers website at https://gain.inl.gov/SitePages/Nuclear%20Energy%20Vouchers.aspx.
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energy source.”149 Congress appropriated $763 million for FES in FY2023, including $242
million for the U.S. contribution to the ITER fusion project, as discussed above.
National Nuclear Security Administration
NNSA’s Inertial Confinement Fusion program conducts experiments at Lawarence Livermore
National Laboratory’s National Ignition Facility (NIF) and other facilities to create miniature
fusion reactions similar to those in nuclear weapons and stars.150 The program received
appropriations of $630 million in FY2023.
ARPA-E
ARPA-E invests in early-stage energy technologies with high potential for transformational
impact, currently including several research programs involving advanced nuclear technologies.
The Modeling-Enhanced Innovations Trailblazing Nuclear Energy Reinvigoration program
(MEITNER), begun in 2018, has since its creation funded nine projects to develop “technologies
to enable lower cost, safer advanced nuclear plant designs.” The Galvanizing Advances in
Market-Aligned Fusion for an Overabundance of Watts (GAMOW), begun in 2020, has funded
14 projects since its creation. The Generating Electricity Managed by Intelligent Nuclear Assets
(GEMINA) program, begun in 2019, has nine projects to “develop digital twin technology for
advanced nuclear reactors and transform operations and maintenance (O&M) systems in the next
generation of nuclear power plants.”151
Offices of Environmental Management and Legacy Management
The DOE’s Office of Environmental Management (EM) and Office of Legacy Management (LM)
provide a variety of functions supporting advanced reactor R&D.
First, EM provides waste management services for ongoing advanced reactor R&D activities. For
example, EM manages the spent nuclear fuel from the Advanced Test Reactor at the Idaho
National Laboratory. DOE describes the Advanced Test Reactor as “the only U.S. research reactor
capable of providing large-volume, high-flux neutron irradiation in a prototype environment … to
study the results of years of intense neutron and gamma radiation on reactor materials and fuels
for … research and power reactors.”152
Second, EM funds and manages environmental remediation and decontamination and
decommissioning for several advanced reactor facilities, including the Energy Technology
Engineering Center at the Santa Susana Field Laboratory in California, various facilities at the
Idaho National Laboratory, and the Hanford site in the state of Washington. At Hanford, EM has
conducted decontamination and decommissioning activities at the Fast Flux Test Facility (FFTF)
since 1992, which operated for 10 years (1982-1992) as a 400 MWt liquid-metal (sodium)-cooled
nuclear research and test reactor to develop and test advanced fuels and materials for the Liquid
Metal Fast-Breeder Reactor Program.
149 DOE Office of Science, “Fusion Energy Sciences (FES),” https://science.osti.gov/fes.
150 Lawrence Livermore National Laboratory, “NIF and Stockpile Stewardship,” https://lasers.llnl.gov/science/nif-and-
stockpile-stewardship.
151 ARPA-E, “Search Our Programs,” https://arpa-e.energy.gov/technologies/programs. The keyword “nuclear” and
technical category “generation” were used to find programs related to advanced nuclear technology.
152 Department of Energy, Office of Chief Financial Officer; FY2020 Congressional Budget Request Volume 5;
Environmental Management, DOE/CF-0155; at p. 73 (March 2019).
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Third, EM funds facility overhead operations for facilities where advanced reactor R&D is
occurring or planned. “Overhead” costs can include infrastructure maintenance (e.g., power,
water, roads, bridges), site safeguards and security, worker health and safety, and program
direction and administration. For example, EM funds site overhead costs at the Hanford Site,
home of Pacific Northwest Laboratory.
Congressional Issues
Role of the Federal Government in Technology Development
What is the appropriate level of federal support for each stage of technology development? That
is a fundamental question in the longstanding national debate over R&D policy writ large. For
nuclear energy technology development, major stages include research on fuels and materials,
development of reactor concepts and designs, component testing and evaluation, licensing by
NRC, demonstration, and commercialization. Typically, the earliest stages of development
involve laboratory-scale work and computer modeling and simulation, some of which may be
relatively inexpensive and applicable to a broad range of nuclear technology. The later stages
focus on specific reactor designs and require construction of full- or nearly full-scale nuclear
power plants potentially costing billions of dollars. Even early-stage nuclear research often
requires the construction and operation of test reactors, shielded hot cells for remote handling of
intensely radioactive materials, and other expensive facilities and infrastructure.
A 2023 report by the Nuclear Innovation Alliance called for DOE to support a “diverse selection
of early-stage advanced nuclear energy technologies” to lay the groundwork for demonstration
and commercialization of those that prove most promising. By giving these technologies “several
rounds of funding in small increments,” DOE would develop “a technology portfolio that sorts a
large number of ideas according to their level of feasibility.” This approach, according to the
report, “increases the likelihood that a greater number of viable technologies will emerge for
DOE to select from for demonstrations.”153
The 116th and 117th Congresses—along with the Trump and Biden administrations—accelerated
funding for all stages of advanced nuclear reactor development, and particularly for the expensive
demonstration phase. In 2021, Congress appropriated through the IIJA $2.477 billion for the
Advanced Reactor Demonstration Program (divided in annual amounts through FY2025, to
remain available until expended), in addition to regular DOE appropriations for the program.
Funding for DOE’s Nuclear Energy account in annual appropriations bills steadily rose from
$1.493 billion in FY2020 to $1.773 billion in FY2023 (up 18%).154 “Nuclear energy is a key
element of the President’s plan to put the United States on a path to net-zero emissions by 2050,”
according to DOE’s FY2023 budget justification. Interest in advanced nuclear reactors, including
oversight of previously appropriated funding, is likely to continue in the 118th Congress.
153 Nuclear Innovation Alliance, Transforming the U.S. Department of Energy: Paving the Way to Commercialize
Advanced Nuclear Energy, January 2023, p. 19, https://nuclearinnovationalliance.org/transforming-us-departmentenergy-paving-way-commercialize-advanced-nuclear-energy.
154 Annual appropriations acts for FY2020 through FY2023, CRS, Appropriations Status Table,” https://www.crs.gov/
AppropriationsStatusTable/Index.
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Perceived Need for Advanced Nuclear Power and Competing
Alternatives
EIA projects that world electricity generation will grow by more than 40% between 2020 and
2040. While renewable energy and nuclear power are projected to rise substantially during that
period, fossil fuels would still constitute about 40% of total generation if current policies and
trends continue.155 Proponents of unconventional nuclear power contend that advanced reactors
could mitigate the concerns about safety, cost, radioactive waste, weapons proliferation, and fuel
supply that are seen as inhibiting greater utilization of nuclear energy. Under that view, advanced
nuclear technology would be indispensable for meeting the world’s rapidly increasing demand for
electricity without emitting greenhouse gases.
“In the 21st century the world faces the new challenge of drastically reducing emissions of
greenhouse gases while simultaneously expanding energy access and economic opportunity to
billions of people,” according to a 2018 study by the Massachusetts Institute of Technology. The
study found that the cost of worldwide greenhouse gas reductions could be minimized by the
deployment of lower-cost nuclear generation.156 A 2021 IAEA report asserted, “Nuclear energy is
key to achieving global net zero objectives, working in partnership with renewable energy
sources and other low carbon options, as part of a sustainable energy system to decarbonize
electricity and non-electric energy production.”157
That finding is disputed by various environmental and other groups that contend that a
combination of renewable energy and efficiency is the lowest-cost option for eliminating
greenhouse gas emissions and could be implemented more quickly. “With technology already
available, renewable energy sources like wind, solar, and geothermal can provide 96 percent of
our electricity and 98 percent of heating demand—the vast majority of U.S. energy use,”
according to the environmental advocacy group Greenpeace USA.158 Some environmental groups
contend that the safety and other risks posed by nuclear energy make it unacceptable in any case,
even with advanced technology. The Nuclear Information and Resource Service advocacy group
says, “There is nothing environmentally friendly about nuclear power. It only creates different
environmental problems than fossil fuel energy sources. But neither fossil fuels nor nuclear power
are safe, sustainable, or healthy for humans and the environment.”159
Germany adopted a policy after the 2011 Fukushima disaster to greatly reduce carbon emissions
through renewable energy and efficiency while eliminating nuclear power. The policy, called
“Energiewende,” or energy transition, calls for Germany’s consumption of primary energy (the
initial energy content of fuels and other energy sources) to be reduced by 50% in 2050 from its
2008 level, while greatly increasing the use of renewable energy throughout the economy.
According to the German government, “By 2050 renewable energies should make up 60 percent
of the gross final consumption of energy, and 80 percent of the gross electricity consumption.”160
155 Energy Information Administration, International Energy Outlook 2021, October 2021, Table E1.gen, electricity
generation: World, Reference case, https://www.eia.gov/outlooks/ieo/tables_side_xls.php.
156 Massachusetts Institute of Technology, “The Future of Nuclear Energy in a Carbon-Constrained World.”
157 IAEA, Nuclear Energy for a Net Zero World, September 2021, https://www.iaea.org/sites/default/files/21/10/
nuclear-energy-for-a-net-zero-world.pdf.
158 Greenpeace USA, “Fighting Global Warming,” November 21, 2018, https://www.greenpeace.org/usa/globalwarming/.
159 Nuclear Information and Resource Service, “Nuclear Energy Frequently Asked Questions,” November 21, 2018,
https://www.nirs.org/basics-of-nuclear-power/nuclear-power-frequently-asked-questions/.
160 German Federal Ministry of Education and Research, “German Energy Transition,” viewed December 22, 2022,
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A 2017 study by an academic team developed “roadmaps” for 139 countries to convert to 100%
renewable energy by 2050. The study concluded that renewable energy production could be
expanded with more certainty than nuclear and other non-emitting sources.161 In response to the
loss of natural gas supplies caused by Russia’s invasion of Ukraine in February 2022, Germany
has delayed the permanent shutdown of its final three operating reactors until April 2023 and has
reopened some coal-fired power plants.162
The National Renewable Energy Laboratory issued a study in 2012 of the impact of increasing
U.S. renewable electricity generation to up to 90% by 2050. The study found that renewables
could “adequately supply 80% of total U.S. electricity generation in 2050,” with nuclear, coal,
and gas supplying the remaining 20%. Nuclear power plants were projected to be located almost
entirely east of the Mississippi River for economic and other reasons.163
DOE Hosting of Private-Sector Experimental Reactors
NEICA authorizes DOE to host privately funded experimental and demonstration reactors, with
the expectation that reactor developers could benefit from the expertise and facilities at DOE
national laboratories. Safety oversight of private-sector experimental reactors at national
laboratories could possibly be conducted by DOE and not require NRC licensing,164 but NEICA
specifies that reactors intended to demonstrate commercial suitability would require NRC
licenses, even at DOE sites.
NEICA added Section 958 to the Energy Policy Act of 2005 (P.L. 109-58), which authorizes a
DOE National Reactor Innovation Center (NRIC). This program would “enable the testing and
demonstration of reactor concepts to be proposed and funded, in whole or in part, by the private
sector.” Such testing and demonstration would take place at DOE national laboratories or other
Department-owned sites. In implementing the NRIC program, DOE is required to coordinate with
NRC on sharing technical expertise on the advanced reactor technologies under development.
DOE signed an agreement on February 17, 2016, with UAMPS to provide a potential site for a
first-of-a-kind NuScale SMR plant at INL, called the Carbon Free Power Project. Under the
agreement, UAMPS is to identify a suitable location at the 890-square-mile INL site, with DOE’s
concurrence, for construction of the plant.165 NRC published its final design certification rule for
a NuScale plant with up to a dozen 50 MWe modules on January 19, 2023.166 On January 4, 2023,
https://www.bmbf.de/bmbf/en/research/energy-and-economy/german-energy-transition/german-energytransition_node.html.
161 Mark Z. Jacobson et al., “100% Clean and Renewable Wind, Water, and Sunlight All-Sector Energy Roadmaps for
139 Countries of the World,” Joule, September 6, 2017, http://web.stanford.edu/group/efmh/jacobson/Articles/I/
CountriesWWS.pdf.
162 World Nuclear Association, “Nuclear Power in Germaney,” October 2022, https://world-nuclear.org/informationlibrary/country-profiles/countries-g-n/germany.aspx; Robert Bryce, “The Iron Law of Electricity Strikes Again:
Germany Re-Opens Five Lignite-Fired Power Plants,” Forbes, October 28, 2022, https://www.forbes.com/sites/
robertbryce/2022/10/28/the-iron-law-of-electricity-strikes-again-germany-re-opens-five-lignite-fired-power-plants.
163 National Renewable Energy Laboratory, Renewable Energy Futures Study, 2012, https://www.nrel.gov/analysis/refutures.html.
164 Todd Garvey, “NRC Licensing of Proposed DOE Nuclear Facilities,” memorandum for the House Committee on
Science, Space, and Technology, July 20, 2015, https://docs.house.gov/meetings/SY/SY20/20150729/103833/HHRG114-SY20-20150729-SD009.pdf.
165 U.S. Department Of Energy Use Permit No. DE-NE700065, February 17, 2016, https://www.id.energy.gov/
insideneid/PDF/DOE_UAMPS%20Use%20Permit%20DE-N700065.pdf.
166 NRC, “NuScale Small Modular Reactor Design Certification,” 88 Federal Register 3287, January 19, 2023,
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NuScale announced its submission of an application to NRC for standard design approval of a
plant with six 77 MWe modules.167
Funding of Demonstration Reactors
A crucial stage in the commercialization of nuclear technology is the construction of
demonstration reactors, which are expected to cost several billion dollars apiece, depending on
their size and level of technical maturity. For example, in 2022, the Natrium demonstration plant
and its separate fuel fabrication facility were estimated to cost $4 billion to construct.168 Including
the demonstration stage, bringing a new reactor technology to the market could require up to 30
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