NRC Issues New Licensing Pathway for Advanced Reactors

The U.S. Nuclear Regulatory Commission (NRC) voted to approve the issuance of a new set of regulations for advanced reactor licensing—the long-awaited 10 CFR Part 53. The new rule crystalizes decades of policy, regulatory and technical developments into an alternative reactor licensing pathway.  

The existing reactor licensing framework was used to license the current fleet of large, light-water reactor operating plants and the regulations—in 10 CFR Part 50 (for a two-step licensing processing) and 10 CFR Part 52 (for a one-step licensing processing)—are largely tailored for that type of reactor. But many advanced reactor designs being developed today do not fit neatly into this framework.

To address this gap, Congress directed the NRC back in 2019 to develop a new regulatory framework for reactors that is risk-informed, performance-based and technology-inclusive, and therefore applicable to a broader range of reactor designs. This is the Part 53 rulemaking. Instead of relying on costly and time-intensive exemptions or workarounds, advanced reactor developers have the option to use Part 53.

Some key takeaways for the new Part 53:

• Provides an alternative, not a replacement, to 10 CFR Parts 50 and 52
• Inherently accommodates advanced and non-light-water reactors
• Focuses on applicant-defined, risk-informed safety cases
• Introduces flexibility in siting, manufacturing, operations and licensing structure

These changes are structural. They affect how the NRC evaluates safety and how applicants develop and present their licensing basis, redefining the regulatory framework within which those projects operate.

How We Got Here

Part 53 is the first new set of reactor licensing regulations since Part 52 in 1989, and the first significant shift in the underlying approach to reactor licensing since Part 50 was introduced in 1956. It is the product of a sustained effort over nearly two decades, reflecting both internal NRC initiatives and congressional direction.

• The existing licensing framework reflects traditional reactors—not advanced ones. The NRC has long recognized that its reactor licensing framework—10 CFR Parts 50 and 52, introduced in 1956 and 1989, respectively—was developed around the existing fleet of light-water reactors. Parts 50 and 52 provide the licensing requirements to construct and operate a nuclear reactor in the United States. The NRC deployed and tailored these regulations in a context dominated by light-water reactors—and as a result, they include prescriptive requirements specific to those technologies.
• The NRC made some early strides to reform its licensing approach. As both reactor operation and technological capabilities matured, the NRC and industry began developing methodologies to use more risk-informed tools, like probabilistic risk assessment (PRA), as a central element of licensing. Starting in the mid-2000s, the NRC began exploring ways to incorporate risk-informed and performance-based approaches into its regulations. It issued policy statements and rulemaking initiatives but instituted no formal regulatory changes. Increasing interaction with advanced reactor developers and the U.S. Department of Energy led to the Licensing Modernization Project, which provided foundational principles and methods for technology-inclusive licensing. But the Part 50 and Part 52 frameworks still remained light-water reactor-based and prescriptive.
• Congress directed a new rule to formalize this progress. The Nuclear Energy Innovation and Modernization Act (2019) directed the NRC to develop a technology-inclusive, risk-informed licensing framework by the end of 2027. The ADVANCE Act (2024) further reinforced that mandate and emphasized the need for a framework capable of accommodating a broader range of reactor technologies and deployment models.

The Part 53 rulemaking has been underway for several years and finally reached its endpoint. The rulemaking reflects years of policy development, stakeholder engagement and technical work in a single, optional licensing framework.

The New Part 53: A Structural Shift

In establishing a new reactor licensing pathway, Part 53 does not just streamline or modernize nuclear reactor licensing—rather it fundamentally reorganizes the reactor licensing framework around three binding regulatory constructs:

• Risk-informed regulation, in which risk insights—derived from PRA and related methodologies—play a central role in safety decisions. Instead of relying solely on a deterministic approach, which focuses on a defined set of requirements, a risk-informed approach integrates analysis about how and why failures could occur—and tailors requirements accordingly.
• Performance-based requirements, which focus on achieving defined safety outcomes rather than prescribing specific design approaches. In other words, the focus is on results, not how those results are attained. Safety is still paramount—the Commission still determines whether a safety case is adequate—but the nature of the review differs, placing greater weight and scrutiny on an applicant’s safety analysis.
• Technology inclusivity, which allows the same regulatory framework to be applied across a range of reactor designs and uses. The old model required non-light-water reactor applicants to rely on exemptions or fit their designs into mismatched regulatory assumptions. A technology-inclusive approach develops the licensing basis around the characteristics of the design itself.

Complementing these principles, the rule introduces flexibility in the use of codes and standards, the classification of structures, systems and components, and operational requirements, with those elements scaled to their safety significance. Part 53 also provides multiple licensing pathways and supports different development approaches, including staged licensing and the use of standardized designs.

These structural differences allow Part 53 to be more adaptable to advanced reactor designs, including non-light-water technologies, for applicants who choose to use it.

What’s Actually in Part 53

Part 53 includes a number of specific regulatory changes that reflect its risk-informed, performance-based and technology-inclusive structure. These are not incremental adjustments—they affect how plants are designed, licensed and operated in practice. Some of the highlights of the new rule include:

• Flexible use of risk methodologies: Requires explicit consideration of risk through PRA, other systematic risk evaluation methods, or a combination of both. These tools are used to generate risk insights and to assess and manage safety.
• Generally licensed reactor operators (GLROs): Allows certain facilities—particularly those with self-reliant mitigation features, e.g., no reliance on humans to implement core safety functions—to operate under a general license framework, reducing the need for site-specific operator licensing in defined circumstances.
• Alternative siting criteria: Provides an alternative to the traditional preference for low-population-density siting by allowing siting decisions based on assessments of societal risk and comparative benefit, including in more densely populated areas. This change reflects advanced reactors’ smaller footprint and reduced chance of radioactive material release compared to large light-water reactors.
• Factory fuel loading: Permits reactors to be fueled at the manufacturing site and transported in a fueled condition to the operating site for use under an NRC license. This is a seismic shift from historic reactor licensing, in which on-site fuel loading marks the shift from construction to operation.
• Expanded use of codes and standards: Allows use of generally accepted codes and standards—including non-nuclear standards—scaled to the safety significance of structures, systems and components (SSCs), as well as use of commercial-grade components where appropriate.
• Departure from the single failure criterion: Eliminates reliance on predefined failure scenarios as a design basis requirement. Instead, safety is demonstrated through integrated, risk-informed analysis, including reliability evaluation, defense-in-depth, and performance monitoring.
• Integrated hazard assessment (including aircraft impacts): Replaces standalone design-basis requirements (such as aircraft impact analysis) with a comprehensive evaluation of internal hazards, external hazards and security threats, including mitigation of large-scale plant impacts.
• Reduced need for additional approvals: The risk-informed approach to managing plant equipment and programmatic controls provides greater operational flexibility and may reduce the need for future exemptions or license amendments.
• Functional containment: Allows containment to be achieved through one or more barriers working together to limit the release of radioactive material, rather than relying solely on a traditional, single containment structure.
• Flexible staffing models: Supports staffing approaches tailored to the design and operational characteristics of the facility, including reduced staffing for smaller or more automated plants.
• Remote operations: Allows certain operations and maintenance activities to be performed remotely, including from locations outside the owner-controlled area, provided safety-significant systems remain within design parameters.
• Load following: Allows plants to automatically adjust output in response to external signals or grid demand, supporting integration with modern electricity systems.
• First-of-a-kind (FOAK) licensing pathways: Allows early projects to establish a licensing basis that can be referenced in subsequent applications, supporting replication and standardization.
• Standardized design finality: Extends regulatory finality to standardized design approvals, including when referenced in later design certification or licensing applications.
• Fitness for duty (Part 26): Establishes a more flexible, risk-informed framework for fitness-for-duty requirements, including alternatives for drug and alcohol testing suited to a wider range of facility types and staffing models.
• Physical security (Part 73): Introduces a performance-based and technology-inclusive security framework, with requirements scaled to the risk profile and characteristics of the facility.

Implications for Applicants and Key Takeaways

The Part 53 framework changes the balance in the licensing process in several ways. Some of the more impactful consequences are likely to include:

• Greater flexibility paired with a higher analytical burden. Part 53 reduces reliance on prescriptive requirements developed for light-water reactors, which can simplify certain aspects of design and reduce the need for exemptions. At the same time, it increases the analytical burden on applicants. Developing a coherent and defensible safety case—supported by probabilistic and systematic risk analysis—becomes central to the licensing process. Applicants must prepare for greater emphasis on the quality of their risk analysis, the integration of design and operational controls, and their ability to explain and defend the overall safety case. In that sense, Part 53 introduces both flexibility and discipline. It expands the range of acceptable approaches but requires a higher degree of analytical rigor in how those approaches are justified.
• Trying to align licensing with modern technologies/deployment pathways. The new rule also reflects an effort to align the regulatory framework with how modern reactor projects are expected to be developed and deployed. As a result, applicants may find their regulatory and commercial planning overlap more seamlessly. For example, Part 53 introduces alternative siting criteria that may allow siting closer to load centers or in conjunction with industrial facilities—a key consideration as domestic energy demand explodes. It also enables operational approaches such as remote operations, reduced staffing and automated load-following—regulatory constraints that can drive staffing and operational decisions.
• Enabling standardization, replication and scalable deployment. The rule supports staged licensing, first-of-a-kind project development and the use of standardized designs, which are important for replication and broader deployment. As nuclear power is poised to grow, a predictable, repeatable licensing framework for both first- and nth-of-a-kind reactors provides a necessary foundation.

While the new rule does not necessarily simplify reactor licensing, it does change how safety is evaluated and demonstrated within the licensing process—focusing on risk-informed and performance-based analyses.

Whether Part 53 proves to be a more effective reactor licensing framework for advanced reactors may depend on its implementation. Regardless, it represents a long-developed yet seismic shift in how the NRC formally regulates nuclear reactors.