In This Issue
Summer Bridge on Engineering the Energy Transition
June 26, 2023 Volume 53 Issue 2
This issue explores the energy transition needed to address the mounting threats of climate change. The articles are an excellent resource to help inform meaningful decisions and steps for energy-related contributions to reduce carbon emissions.

New Generation Resources: Advanced Reactors, Fusion, Hydrogen

Wednesday, June 7, 2023

Author: Kathryn A. McCarthy, Jess C. Gehin, Vivek A. Sujan, and Lynne K. Degitz

Deployment of advanced reactors, clean hydrogen, and fusion energy requires private-public partnerships, investment, streamlined regulations, international cooperation, and policy support.

Decarbonization of the global economy in the near term necessarily focuses on current energy options for industrial and consumer applications. In addition, new carbon-free energy resources with higher power density are essential for a full energy transition and continued energy evolution (Smil 2021). In this article we examine opportunities and challenges to be addressed for advanced nuclear, hydrogen, and fusion energy.

Setting the Stage for Nuclear, Hydrogen, and Fusion Energy

Advanced nuclear reactors,[1] poised to come online within a decade, may augment baseload power options while also managing costs through modular fabrication, new fuel cycles, and distributed installation (IEA and NEA 2020). For hydrogen, a new national strategy advocates for the accelerated development of low-carbon and clean hydrogen production for targeted sectors such as manufacturing, heavy-duty transportation, and long-duration energy storage (DOE 2022a). Nuclear fusion, while less mature, has compelling potential as the natural progression of advanced nuclear energy for delivering broadly available, safe, carbon-free energy with limited waste products (Gonzalez et al. 2022; NASEM 2021).

New energy solutions are unlikely to succeed without community acceptance and understanding of environmental impacts.

Nuclear and fusion systems are energy sources, while hydrogen is an energy carrier—and can, like electricity, support the use of various energy sources. The three approaches vary significantly in their readiness for deployment, but each offers valuable characteristics for a future carbon-free energy portfolio.

All new energy resources require extended periods of development, including resolution of technical challenges, demonstration of economic feasibility and cost predictability, public acceptance, safety and regulatory certainty, utility acceptance, and grid integration.[2] New resources also offer an opportunity to address environmental concerns and energy justice from an early stage of development. Without community acceptance and other aspects of energy justice, as well as an understanding of environmental impacts, new energy solutions are unlikely to succeed (Hoedl 2019).

A proposal now under review to site advanced nuclear reactors at former coal plants is one example of how a blend of government, industry, and community engagement can support energy evolution (Hansen et al. 2022). New analysis tools can also support local planning efforts to inform options for future power plant siting and energy source access (Omitaomu et al. 2022).

Needed Technology Development

Advanced Nuclear Reactors

Advanced nuclear systems, including small modular reactors, are closest to achieving both demonstration facilities and commercial deployment. These reactors include a variety of designs and capabilities, ranging from 10 to 100s of megawatts.

Light water reactor (LWR) designs have a more defined path to commercialization in the United States because they share similarities with already licensed and operating reactors.[3] Non-LWR designs require significant investment in research and development to qualify fuels and materials; qualification requires validation of modeling and simulation tools, and potentially component testing.

Fuel development for advanced nuclear systems ranges from improvements to LWR fuels to new forms based on alternative fuels and cladding, all with differing levels of technology readiness (Carmack et al. 2017). Coated particle fuels, for example, are undergoing testing and changes that could benefit performance; they are being explored to support development and demonstration of high-temperature reactors (Demkowicz et al. 2019). Additionally, the development of new materials for reactor structures is necessary for harsh advanced reactor environments (Zinkle et al. 2016). Computing, modeling, and simulation capabilities are advancing nuclear systems with both new (Alexander et al. 2020; Martineau 2021) and existing models such as MELCOR at Sandia National Laboratory.[4]


Hydrogen (H2) can be extracted from fossil fuels and biomass, from water, or from a mix of both; however, thermal processes using natural gas or coal are currently the primary source of H2 production (IEA 2019). To contribute to decarbonization, economical, low-carbon or carbon-free production techniques must be developed to yield “clean hydrogen” (IEA 2019).

The DOE Hydrogen Shot[5] seeks to reduce the cost of clean hydrogen by 80 percent—to $1 per kilogram in a decade. Technical challenges must be resolved related to H2 distribution, storage, dispensing, and safety. Long-term distribution of pure hydrogen through the existing natural gas pipeline infrastructure is limited because of hydrogen’s corrosive impact on materials (Topolski et al. 2022). Long-term storage materials for hydrogen must also be addressed, and safe end-use solutions must be developed for diverse applications.

In short, the infrastructure required for clean hydrogen is similar to the scale of conventional fossil fuel infrastructure. One important difference is that hydrogen can be produced in a centralized facility or at distributed end-use locations (DOE 2017).


Fusion could be a compelling energy source, and there has been exciting technical progress over the past decade:

  • The ITER facility in southern France is demonstrating that it is possible to achieve millimeter-scale engineering precision for assembly of power plant–scale fusion reactor components (Bigot 2022).
  • Early in 2022 the Joint European Torus (JET) in the United Kingdom documented the generation of 59 megajoules of sustained fusion energy, more than doubling its 1997 record and providing confidence in the physics underlying ITER (Gibney 2022).
  • The National Ignition Facility at Lawrence Livermore National Laboratory achieved ignition (Bishop 2022) late in 2022, demonstrating a “Q” of around 1.5 (the energy produced by the target divided by the energy that went into the target) (Zylstra et al. 2022).

Investment in the private fusion industry has grown to about $5 billion, with more than 30 companies now established worldwide (Windridge 2022). Still, significant technical challenges must be solved for fusion to be a practical, economical energy source (figure 1). ITER will address one of these challenges: the production and control of a self-sustaining fusion power source with a Q of up to 10. The development of materials that can survive fusion power plant conditions and the establishment of a sustainable fusion fuel cycle are at much earlier stages of technical maturity. While ITER will contribute to solving these challenges, additional investment is needed. All three challenges must be resolved to construct and operate a pilot plant that demonstrates a safe, affordable, and reliable fusion energy system (FES Advisory Committee 2020).

McCarthy Figure 1.gif

Economic Factors: Cost, Supply Chains, Infrastructure

Advanced Nuclear Reactors

Nuclear fission energy has been deployed in the United States at a large scale for over 40 years and now delivers nearly 20 percent of the country’s electricity generation (EIA 2023) and about 50 percent of its carbon-free electricity (DOE 2022b). However, cost predictability is a persistent issue.

Small modular reactors (Liou 2021), developed in response to the challenges of deploying large-scale reactors (NEA and OECD 2016), provide benefits such as reduced capital costs, more reliance on passive safety, and greater flexibility for deployment. A broad range of designs is under development, with a variety of fuels and coolants (MIT 2018). While these designs reduce overall manufacturing and construction costs—and offer new options for remote site installation—cost competitiveness is still uncertain and there remain issues with fuel supply chain development. The Department of Energy Advanced Reactor Demonstration Program,[6] which supports deployment of first-of-a-kind advanced reactors, will provide important data on competitiveness, but ultimately deployment of multiple advanced reactors will be needed to evaluate cost consistency.

Further, many advanced reactors use High Assay Low Enriched Uranium (HALEU), which is not produced in the United States. National investment is needed to establish the required infrastructure for this fuel (MIT 2018). In November 2022 DOE announced a cost-shared award for the first domestic production of HALEU for advanced nuclear reactors (DOE 2022c). Figure 2 illustrates an advanced reactor deployment timeline.

McCarthy Figure 2.gif


Economical clean H2 production could be accelerated by new carbon-free energy sources, such as advanced reactors. Innovations in other industries, including transportation, chemical and steel production, and pipeline infrastructure, could also affect hydrogen’s economic feasibility (DOE 2022a).

The hydrogen energy value chain to the end user will largely consist of three stages: production, distribution/storage, and dispensing. The final dispensed price and carbon footprint of hydrogen are the combination of costs incurred and CO2 generated during these stages (Sujan 2022). Additional factors—such as economic profit margins, H2 purity, taxes, incentives, environmental policies, public-private partnerships, upstream feedstock carbon footprints, end-use productivity, and resiliency—must also be considered.


Fusion will have to be competitive with other firm energy resources, such as advanced reactors and hydrogen. And fusion power plants must offer utilities compelling options at a sufficient scale and availability (NASEM 2021). Some posit that fusion is likely to follow a trajectory similar to that of nuclear fission, with costs decreasing as efficiency improves (Griffiths et al. 2022).

Current R&D focuses on resolving technical chal-lenges and establishing viable solutions for the sustained operation of a fusion pilot plant. Private fusion companies are exploring compact options for future fusion devices that may prove more economical. The bottom line is that a pilot fusion power plant must not only demonstrate technical features for future power plants but also give confidence to utilities that the economics for the technology will be acceptable for commercial deployment.

The Role of Utilities

Utility acceptance is a key factor in the deployment of any new energy source. Many utilities already own and operate nuclear fission reactors, and the recently established DOE clean H2 hubs (part of the department’s Energy Earthshots[7]) should accelerate utility acceptance of hydrogen. Engaging utilities during the development of fusion energy has been identified as an important step for utility acceptance (NASEM 2021). Similarly, public acceptance of a new energy source is as important to deployment as is the technology development. Recommended methods for public acceptance include early engagement and consent-based siting (Kasperson and Ram 2013).

Safety and Regulation

Advanced Reactors

Regulatory frameworks need to be modernized to reflect the unique characteristics of advanced reactors and eliminate unnecessary delays (Meserve 2020). This includes streamlining licensing processes and establishing standardized safety criteria. Licensing for advanced reactors is being pursued through existing regulations largely established for light water reactors. The US Nuclear Regulatory Commission (USNRC) is pursuing new rule making to develop a risk-informed, technology-inclusive regulatory framework for advanced reactors (USNRC 2023a). Advanced LWRs, and in particular small -modular LWRs, have a simpler path to commercialization since the USNRC has many years of experience with LWRs (Federal Register 2023; USNRC 2022). In addition, the industry-led Licensing Moderniza-tion Project has been approved by the USNRC for use with current regulations to provide a path for advanced -reactors that are ready for licensing before 2027 (-Grabaskas et al. 2019). This is important for the Carbon Free Power Project, for example; it notified the USNRC that it intends to submit a combined license application for the NuScale SMR in 2024 (CFPP 2022).

Regulatory frameworks need to be modernized to reflect the unique characteristics of advanced reactors and eliminate unnecessary delays.


Efficient, safe deployment of hydrogen requires infrastructure solutions that are well aligned with the needs of the end user, whether for industrial applications or consumers.

Because hydrogen is more flammable than methane and other hydrocarbon fuels, its use may require the installation of sensors and instrumentation specifically configured for fuels containing hydrogen. In addition, hydrogen can affect materials and systems differently than other gases. Solutions that use liquid hydrogen will introduce challenges with the safe handling of cryogenic fluids and therefore federal and local regulatory agencies[8] will need to coordinate in establishing and maintaining H2 standards.

Regulatory compliance and oversight will be critical in all phases of the H2 value chain, from production through off-take usage. While some standards and regulations are in place, gaps remain in areas such as offshore transportation, sales and distribution, fuel certification, and residential and commercial heating (Ehrhart et al. 2021).


The USNRC (2023b) is developing a licensing framework for fusion, to be completed by 2027. This is a challenging undertaking since many fusion tech-nologies are still at a low level of technology readiness, and the fusion configurations in development vary widely. Many, but not all, concepts assume a deuterium-tritium fuel cycle. There are also concepts for fusion-fission hybrids, primarily for destruction of long-lived transuranics (Shlenskii and Kuteev 2020).

Fusion systems can produce copious neutrons, activating reactor structures and requiring longer-term management solutions. Work is needed to ensure availability of “low-activation” materials that are easier to dispose of than those currently used in a nuclear system (Jones et al. 1999; Petti et al. 2000). Safe operation scenarios must be demonstrated, and regulatory certainty is needed both for the development of appropriate down-selection of fusion system approaches and for utility owner-operator acceptance (EIA 2023).

The Path Ahead

The cost- and time-efficient deployment of advanced reactors, clean hydrogen, and fusion requires a coordinated effort involving private-public partnerships, sustained investment, a tailored regulatory process, international cooperation, and policy support.

The private sector brings expertise in business -models, financing, and commercialization, while the public sector offers research, development, and demonstration capabilities. Technical challenges must be resolved, cost and supply chain issues addressed, safety and licensing established, and community support secured for these resources to be viable contributors to carbon-free power generation and other applications. Government and regulatory agencies will need to provide pathways for collaborations that maintain the attributes necessary for market competitiveness. Figure 3 illustrates how these new energy resources can contribute to a clean energy ecosystem.

McCarthy Figure 3.gif

The potential for flexible application, combined with higher energy density, makes the development of these resources especially valuable in a future integrated clean energy system (Bragg-Sitton et al. 2020; DOE 2020). Integrated clean energy systems can deliver more value than the sum of a single resource. Consider an advanced or fusion reactor that provides electricity during peak demand and produces hydrogen during times when demand is low.

Given deployment timelines, we envision that advanced reactors will both provide a carbon-free power source for grid distribution and support localized industrial processes, such as clean hydrogen production. Hydrogen’s flexibility lends itself to serving industrial processes that are particularly difficult to decarbonize, such as ammonia for fertilizer. Fusion could follow advanced reactors with delivery of firm baseload power; it could also be used to help manage the nuclear fuel cycle via transmutation of waste. The goals of long-term decarbonization and new clean energy source development are deeply compatible.


This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (


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[1]  Advanced reactors are nuclear fission reactors with technologies that provide significant improvements over current light water reactors in performance, passive safety features, thermal efficiency, and expanded applications.

[2]  International Energy Agency, “Net zero by 2050: A roadmap for the global energy sector” (

[3]  One example is NuScale’s standard design certification for an integrated assembly of 12 small modular reactors, submitted to the US Nuclear Regulatory Commission (USNRC 2017).

[4]  MELCOR (a portmanteau from melting core) is a computer code developed at Sandia “to model the progression of severe accidents in nuclear power plants” ( energy-safety-security/melcor/).


[6] program


8]  In addition to the EPA and OSHA, these will include the Pipeline and Hazardous Materials Safety Administration (PHMSA), Federal Motor Carrier Safety Administration (FMCSA), Federal Highway Administration (FHWA), National Fire Protection Association (NFPA), American Society of Mechanical Engineers (ASME), and Compressed Gas Association (CGA).

About the Author:Kathryn McCarthy (NAE) is director, US ITER, Oak Ridge National Laboratory (ORNL). Jess Gehin is associate laboratory director, nuclear science and technology, Idaho National Laboratory. Vivek Sujan is distinguished research staff, energy science and technology, and Lynne Degitz is stakeholder relations advisor, US ITER, both at ORNL.