R. Patrick White* and Liam S. Hines
Edited by Jameson R. McBride and Grant A. Knappe
Article | Aug. 30, 2021
*Email: rpwhite@mit.edu
DOI: 10.38105/zv7f0d3vxd
Highlights
- Renewed interest in fusion technology as a possible clean energy source is driving investment in the development, design, and deployment of commercial fusion power plants.
- The regulatory pathway in the United States for commercial fusion is unclear due to the lack of operating experience.
- Industry proposals to use risk-informed regulatory approaches for initial commercial fusion projects could complicate the licensing process for a first-of-a-kind fusion facility and delay near-term commercial deployment.
- A hybrid deterministic and risk-informed regulatory process that incorporates seven decades of lessons learned in commercial fission could enable the implementation of regulatory requirements that evolve in parallel with the development of commercial fusion facilities.
- This new regulatory approach could enable more rapid deployment of commercial fusion technology and facilitate long-term regulatory stability as fusion energy develops from a first-of-a-kind demonstration technology to a mature low-carbon energy source.
Article Summary
Fusion energy has long been touted as an energy source
capable of producing large amounts of clean energy
without the fuel, pollution, siting, and safety constraints
of other energy sources. Despite this promise, fusion
energy has not come to fruition after six decades of
research and development due to continuing scientific
and technical challenges. Significant private investment in
commercial fusion start-ups signals a renewed interest in the
prospects of near-term development of fusion technology.
Successful deployment of fusion energy, however, will require an appropriate regulatory framework to ensure
public safety and economic viability. Initial discussions
and proposals from fusion start-ups (e.g., Commonwealth
Fusion Systems, General Fusion, TAE Technologies) and
industry associations (e.g., Fusion Industry Association)
have advocated the use of risk-informed regulations as the
basis for the licensing of commercial fusion technology in
the United States. These proposals are based, in part, on
regulatory methods used for licensing commercial fission
technology that developed in parallel with the commercial
fission industry.
Risk-informed regulations incorporate risk information
from probabilistic safety analyses to ensure that regulations
are appropriate for the actual risk of an activity. Proponents
of risk-informed regulation believe that these methods can
improve the economics and operation of nuclear facilities
by focusing regulatory resources on addressing credible
accident scenarios that are most likely to pose threats
to worker and public safety. In addition to interest from
industry, the U.S. Nuclear Regulatory Commission (NRC)
has begun an initiative to develop a new risk-informed
regulatory framework for the licensing of advanced nuclear
fission power plants, but it is unclear if this framework
would be applied to fusion. Despite the benefits of
adopting a risk-informed framework for a mature fission
industry, use of risk-informed regulations for the licensing
of first-generation commercial fusion technology could be
detrimental to the goal of economic near-term deployment
of fusion. Commercial fusion technology has an insufficient
operational and regulatory experience base to support the
rapid and effective use of risk-informed regulations. More
conservative regulatory analyses could instead be used
for first-generation fusion facilities to facilitate more rapid
deployment, and enable collection of operating experience
to support future use of risk-informed regulations. A hybrid
regulatory pathway that incorporates seven decades of
lessons learned in commercial fission would enable the
implementation of regulatory requirements that evolve with
the development of commercial fusion technology, from a
first-of-a-kind demonstration plant to a mature low-carbon
energy source.
Fusion energy has been the “holy grail” of energy
production since its conception nearly 70 years ago.
Fusion energy has been touted as an inexhaustible source of
clean energy that could be readily scaled to meet humanity’s
continuously growing energy demands. The new technology
would eliminate many of the constraints of other existing energy sources:
- No fuel constraints: unlike fossil fuels, the different fuels for fusion energy are more abundant – normally consisting of readily available hydrogen isotopes
- No geographic siting constraints: unlike renewable energy, fusion facility siting is not limited based on site conditions such as available wind, solar, hydro, or geothermal resources
- No pollution constraints: unlike fossil fuels or nuclear fission, the main byproducts of fusion reaction are stable, non-toxic gasses such as helium
- No safety constraints: unlike nuclear fission, fusion reactions do not produce long-lived nuclear fission products and would not be vulnerable to nuclear meltdown accidents
Eliminating these constraints makes fusion energy
extremely attractive, and the technology could be poised to
ascend as humanity’s final energy source.
As scientists and engineers began developing fusion
technology, however, technical challenges began to
emerge. Creating, sustaining, controlling, and containing
high temperature fusion reactions required development of
new scientific theories and invention of new engineering
systems. Development of a net energy positive fusion device
has remained elusive to fusion energy developers for decades
as each scientific advancement has revealed new physics or
engineering challenges. Public enthusiasm waned as fusion
energy appeared to always be “30 years away.”
The past 10 years, however, have seen a renewed
interest in fusion energy development. The urgent need to
decarbonize has revitalized interest in development of novel
clean energy sources like fusion, and technical advancements
such as the maturation of high temperature superconducting
magnet technology have spurred private investment in the
development of commercial fusion energy technology [1].
Private fusion energy developers have proposed a wide
variety of technologies for commercial fusion energy facilities
but most have one goal in common: they seek to develop
and demonstrate a commercial scale net energy fusion
device within a decade. Commercial fusion energy developers
are now poised to attempt to overcome the final technical
challenges facing fusion energy.
Regulatory Challenges for Fusion
As commercial developers seek to make fusion energy a reality, they must also begin to address the operational challenges associated with any new energy source. One significant challenge for fusion energy will be the regulation and licensing of commercial fusion energy facilities. The promise of fusion energy is based on the elimination of fuel, siting, pollution, and safety challenges that constrain other energy technologies. While there are fusion technologies that can theoretically eliminate all of the constraints, the physics and engineering realities associated with most approaches to commercial scale fusion have introduced new challenges. The most technically achievable fusion energy reaction (highest reaction rate at achievable operating temperature and most abundant fuel) combines two isotopes of hydrogen (2H – deuterium and 3H – tritium) to form a helium atom and a neutron. Most developers seeking to demonstrate net-energy gain will utilize this deuterium-tritium fusion reaction for their fusion energy facilities.
Figure 1: Regulatory hazards of particular concern for
commercial fusion facilities.
This reaction, however, has safety challenges related to
both the fuel and the reaction products. The tritium fuel
is radioactive (emitting low energy beta radiation) and is
chemically identical to hydrogen, so it is susceptible to
fire, explosions, and leakage from storage vessels unless
properly contained. The structural materials in the fusion
device absorb neutrons produced by the fusion reactions and
become radioactive. Thus, during operation, neutron-activated
radioactive material will be produced inside of the fusion
facility. This radioactive waste will need to be carefully
managed both during and after commercial operations. These
radiological hazards and other industrial hazards can likely
be managed through engineering and operational controls,
but regulation will be needed to ensure the safe operation
of commercial fusion facilities. The regulatory rules for
commercial fusion facilities have not yet been established
and regulators are working to establish appropriate regulatory
frameworks and pathways for commercial fusion.
Figure 1 summarizes the high level hazards that could
be expected at a commercial fusion facility utilizing the
deuterium-tritium fuel cycle. Given the potential radiological
hazards associated with commercial fusion energy, the
regulator for fusion facilities in the United States would be
the Nuclear Regulatory Commission (NRC). The NRC has
previously asserted authority to develop fusion regulations,
but elected to wait for further commercial development
to issue formal fusion regulations [2]. The 2018 Nuclear
Energy Innovation and Modernization Act required the NRC to
address the licensing challenges of advanced nuclear systems
including fusion and prompted the NRC to begin discussions
with stakeholders on the regulation of fusion energy [3].
Fusion energy proponents (specifically the Fusion Industry
Association) have offered several pathways to fusion licensing
under existing regulatory frameworks in initial public meetings
with regulators [4]. It is not yet clear what approach the NRC
will take to license and regulate fusion technology [5].
Uncertainty in the licensing process for commercial fusion
may lead to schedule delays and cost increases, hampering
the economic viability of fusion facilities and dissuading
fusion stakeholders from initiating future projects. Without
a clear long-term plan for commercial fusion licensing, the
regulatory decisions made in licensing the first-generation of
fusion facilities could make or break the viability of fusion
energy. Overburdening regulations that target safety concerns
irrelevant to fusion systems, or technology-specific regulations
that allow for only specific fusion devices to be licensed, could
pose obstacles for a burgeoning fusion industry. Regulators
and developers must seek to develop regulatory frameworks
that properly address the safety hazards of fusion facilities
without hindering the innovation of new technologies [6].
A licensing framework that enables the safe and efficient
regulation of the novel technology is necessary for fusion
energy to succeed.
Characterizing Regulatory Frameworks is Critical
The development of appropriate regulations that facilitate
fusion energy innovation requires an understanding of the
different approaches to regulating technologies, and the
different methods for ensuring that safety concerns are
properly addressed. The most important trade-offs in licensing
fusion energy will be between deterministic and probabilistic
regulations and between prescriptive and performance-based
regulations.
The first dichotomy, deterministic vs. probabilistic,
characterizes how regulations assess safety and risk.
Risk analyses, as they apply to regulation, primarily focus
on three factors known together as the ‘risk triplet’: the
specific sequence of events that define a particular accident,
the probability of that event sequence occurring, and the
consequences should that event sequence occur [7]. The
main difference between deterministic and probabilistic
frameworks is how each factor in the risk triplet is considered
when evaluating risk. Deterministic analyses focus on
engineering analyses and their consequences, without
explicit regard to probability [7]. Deterministic analyses
will tend to emphasize designing for high-consequence,
low-probability event sequences with the assumption that
design for the highest-consequence events will ensure safety
for any lower-consequence events [8].
Probabilistic analyses, by contrast, prioritize the likelihood
of a specific accident sequence occurring when evaluating
risk. Regulations based on probabilistic analyses consider
all three factors of the risk triplet and focus on event
sequences with the greatest consequences and the greatest
probability of occurring [7]. The philosophy of regulation based
on probabilistic analyses maintains that the bounding-case
assumptions of deterministic analyses are not comprehensive,
and that emphasizing highly unlikely but catastrophic accident
scenarios can fail to encapsulate lower consequence events
that are much more likely to pose real threats to public
safety. Selection of deterministic or probabilistic regulatory
frameworks for fusion technologies could reflect how the
risk associated with fusion facility accidents would be most
efficiently and effectively analyzed to protect public safety.
The second dichotomy, prescriptive vs.
performance-based frameworks, describes how facilities
must address and protect against specific accidents. A
prescriptive framework demands facilities take a specific
set of actions or require specific equipment to meet a
particular safety objective [7]. In the case of fission facilities,
a prescriptive requirement could require a facility to have
emergency diesel generators to provide emergency power
to safety systems that cool the nuclear reactor core in order
to meet the safety objective of ensuring that the reactor fuel
does not overheat during a loss of off-site power [9]. Fission
reactor designers are required to have these emergency
diesel generators included in their design as part of the
regulatory requirements. Under a prescriptive framework,
facilities must address safety objectives exactly as instructed
by regulators. While a prescriptive framework provides
regulatory certainty, there is little room for flexibility and
innovation.
A performance-based framework, by contrast, provides
this flexibility. Performance-based regulations instead only
specify what measurable safety objectives must be met,
but allows the licensees flexibility in how they meet this
metric [7]. In the aforementioned case of facility blackouts,
a performance-based framework may require facilities to
demonstrate that their design ensures the reactor core does
not overheat during blackouts but would allow the applicant
to choose how their design achieves this objective [9].
This flexibility, however, comes at the cost of regulatory
certainty [8]. Compared to the prescriptive framework, in which
developers know exactly what a facility needs in order to meet
the conditions of licensing, performance-based frameworks
allow developers to meet safety objectives through novel
approaches. Novel safety approaches can require additional
analyses and safety reviews from regulators to ensure
that new methods to meet performance metrics soundly
address safety objectives. Given the different benefits of
prescriptive and performance-based frameworks, there is no
“one-size-fits-all” regulatory framework; each framework will
produce optimal licensing pathways for different situations.
For the future of fusion energy, a licensing framework that
balances both flexibility and certainty will be essential to
creating a regulatory framework for fusion.
Current Proposed Frameworks for Commercial Fusion Regulation
Nuclear energy regulation in the United States as it exists
today is a deterministic and prescriptive framework focused
on the safety concerns of fission light water reactors (LWRs)
[10]. Existing regulations target the safety concerns of fission
LWRs, such as the control of fission chain reactions in
water-cooled systems, or the release of radioactive fission
products from reactor fuel. The safety concerns for fission
facilities are not applicable to fusion energy and the unique
hazards of fusion (including tritium and fusion neutron activated materials) would need to be separately evaluated.
The historical difficulties of licensing fusion devices under
existing fission regulations has spurred interest from the fusion
industry to develop entirely new regulatory frameworks for
fusion technology that target the specific safety concerns of
fusion systems [4].
A separate licensing framework for fusion energy
would ease many of the complications of adapting
regulations designed for fission to fusion. Proposals
for new fusion regulatory frameworks include not only
tailoring new regulations to the specific safety concerns
of fusion technologies, but also departing from existing
deterministic, prescriptive frameworks to address safety
concerns with probabilistic, performance-based regulations
[11]. Proponents of these approaches believe adopting
a probabilistic performance-based framework can enable
regulatory focus on accident scenarios of greatest concern
to public safety and provide commercial fusion developers
flexibility in pursuing a variety of innovative approaches to
achieve commercially viable fusion energy [11]. A probabilistic
performance-based framework initially appears to provide
the conducive regulatory environment necessary for the
growth of a fusion energy industry. However, the regulatory
and commercial benefits of probabilistic, performance-based
frameworks actually culminate from the maturation of and
development of extensive experience with a technology.
The Challenge of Regulating Fusion with Risk-Informed Frameworks
The risk-informed regulatory frameworks currently under
development for advanced commercial fission systems are
the result of seven decades of technology development
and accumulation of operational experience. The first
generation of commercial fission facilities in the United
States was largely regulated with deterministic and
performance-based regulatory frameworks due to the limited
operational experience with the technology and wide variety
of technologies under development [12]. Emergence of LWR
technology as the dominant reactor technology encouraged
development of prescriptive requirements to create a more
predictable licensing process [13]. The accumulation of
operating experience facilitated the use of risk-informed
methods to reduce the excess engineering conservatisms
associated with deterministic regulation.
The evolution from simplified deterministic methods
to risk-informed methods reflects increasing industry and
regulator understanding of nuclear technology and maturation
of design and analysis processes. These risk-informed
frameworks require a detailed mechanistic understanding
of plant operation and failure modes to develop accurate
failure event sequences and substantial statistical information
from component, system, and facility operation to adequately
model and predict the failure frequencies and probabilities.
Documentation and study of thousands of cumulative years of
commercial fission reactor operation have opened the door for
the effective use of risk-informed frameworks for commercial
fission technology. This experience is what provides the
technical basis for risk-informed models and insights for
fission.
Initial commercial fusion facilities will be groundbreaking
engineering devices, demonstrating at an industrial scale
new engineering and scientific principles. This type of
innovation is exciting for technological progress but will pose a
significant challenge for risk-informed regulatory frameworks.
Commercial fusion facilities will require the use of many
novel technologies and engineering systems that do not
have significant operating experience. The net energy gain
or burning plasma conditions inside of a commercial fusion
device have never been controlled on Earth, and the scientific
basis for the control of these reactions is still incomplete. No
fusion facility has ever produced more than a small amount of
thermal energy and no facility has ever achieved net energy
production. Development of net-energy fusion facilities that
produce hundreds or thousands of megawatts of energy is a
dramatic extrapolation from current experience. There will be
many unknowns as developers seek to control fusion energy
devices in new operational regimes.
Novel technologies can be operated safely, but their
development is an inherently iterative process as scientists
and engineers incorporate lessons learned from the design,
manufacturing, and operation of multiple generations
of devices. The main challenge of using risk-informed
methods for the safety analysis and regulation of commercial
fusion facilities is that these methods require significant
data on component, system, and facility-level operation
to support regulatory decision-making. Developing an
understanding of these operational characteristics to support
risk-informed decision-making would require substantial
testing of components, systems, and facilities [8]. While this
information could likely be gained without the thousands
of reactor-years of operation through thoughtfully-designed
testing programs for fusion technology, the information
would not likely be available for first-generation fusion
commercial fusion technology without significantly delaying
deployment and increasing costs associated with the testing
and regulatory process.
A Hybrid Deterministic and Risk-Informed Regulatory Method Could Enable Rapid Early Deployment and Long Term Regulatory Refinement
Commercial fusion should use the lessons learned from
commercial fission to both enable the rapid deployment of
first-generation fusion technology but embrace the use of risk
information as it becomes available to develop more effective
regulation. The use of simplified deterministic regulatory
methods for first-generation fusion technology would increase
engineering conservatisms of initial facilities but reduce the
uncertainties associated with facility design and licensing. The
reduction in regulatory process uncertainty associated with the
use of deterministic analysis reduces upfront regulatory costs
for technology developers, provides greater assurance of
project completion, and reduces the risk of regulation-related delays that can dramatically increase costs. The resulting
stable, predictable regulatory framework could enable initial
commercial maturation of the fusion industry and allow for
reductions in cost via gradual design standardization and
industry learning-by-doing [14].
Regulatory challenges for some advanced fission
reactors highlights the limitations associated with using
fully risk-informed methods for the regulation of novel
energy technologies. The NRC has shifted towards use of
risk-informed regulation in recent years and continued this
practice in the development of initial regulation of advanced
fission reactors [15]. Initiatives such as the Licensing
Modernization Program intended to increase advanced
reactor regulation effectiveness have run into challenges as
some novel reactor developers would like to use deterministic
analysis for first-of-a-kind reactors [16]. Despite the NRC’s
experience with transitioning from deterministic to probabilistic
analyses, a focus on risk-informed regulation may complicate
the near term regulation and deployment of novel fission
technology.
If first-generation commercial fusion facilities can be
successfully deployed, commercial fusion developers could
leverage accumulated operating experience to develop more
mature models of fusion facility risk. These models could
then be used to reduce engineering conservatism and
costs through risk-informed regulation. A clear regulatory
pathway should be established from the outset for fusion
facilities that allows incorporation of this design and
operational experience into risk analyses for subsequent
commercial fusion designs and facilities. These ongoing
risk analyses can then serve as the technical basis to
meet additional risk-informed regulatory requirements for
subsequent commercial facilities. This process would allow
designers to leverage operational experience to support
use of more realistic regulatory requirements and enable
learning-by-doing on both subsequent builds and licensing
proceedings.
A regulatory framework that fosters the evolution from
deterministic to risk-informed methods for regulating fusion
may enable developers and regulators to utilize operating
experience from first-generation facilities to support licensing
of subsequent facilities. This regulatory framework could
help maximize the efficiency of the development and
design process, and ensure that facilities have sufficient
information to justify their operation. An explicit hybrid
pathway incorporates seven decades of lessons learned
in commercial fission and enables the implementation of
regulatory requirements that evolve with the development
of commercial fusion technology from a first-of-a-kind
demonstration plant to a mature low-carbon energy source.
Policymakers and regulators should work to develop
appropriate policies that enable safe, economic, and
rapid commercialization of the technology while promoting
long-term industry success. Proponents of the fusion industry
should be cognizant of the immaturity of commercial fusion
technology and ensure that they advocate for licensing
pathways that are appropriate for the developing industry.
Regulators should evaluate a variety of regulatory models
and work with applicants to develop a regulatory framework
that protects public safety while facilitating economically
competitive technology innovation. Deliberate development
of a regulatory framework that supports both the initial
deployment of fusion technology in the next 15 years and
subsequent commercial deployments is critical to support
industry development.
Conclusions
Commercial fusion technology has potential as a future source
of low carbon energy that compliments other low carbon
energy sources, but regulatory questions must be resolved
to enable successful development and deployment. Initial
proposals for regulation of commercial fusion technology
have highlighted industry interest in risk-informed regulations,
but inappropriate use of risk-informed frameworks could be
detrimental to the goal of economic near-term deployment
due to limited design and operational experience with
fusion technology. Lessons learned from the regulation of
commercial fission technology suggest that an evolutionary
regulatory approach using deterministic requirements for
first-generation technology and implementing risk-informed
requirements once the technology matures could minimize the
regulatory burden for commercial fusion technology. Industry,
regulators, and policymakers should carefully consider the
potential implications of regulatory frameworks on the
development and deployment of fusion technology before
inadvertently creating requirements that could inhibit the
development of commercial fusion technology.
Citation
White, R. P. & Hines. L. S. Do proposed regulatory
approaches for commercial fusion energy jeopardize
successful technology deployment? MIT Science Policy
Review 2, 40-45 (2021). https://doi.org/10.38105/
spr.zv7f0d3vxd.
Open Access
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