Redesigning nuclear regulation: How US and UK frameworks are evolving to support advanced nuclear technologies

This article was published in our nuclear briefing, Nucleus.

Part 53 to Title 10 of the Code of Federal Regulations, Risk-Informed, Technology-Inclusive Regulatory Framework for Advanced Reactors, is a new rule issued by the US Nuclear Regulatory Commission (NRC), representing a significant shift towards modern, flexible regulation for advanced nuclear reactors. It became effective on 29 April 2026.

It establishes a risk-informed, performance-based licensing framework that aims to modernise and streamline the regulatory process, making it more flexible and efficient for next-generation technologies. The framework provides an additional option for advanced reactors, without replacing existing licensing rules and pathways.

The UK is pursuing its own regulatory evolution to support the acceleration of new nuclear deployment. In late May, the nuclear regulators for Great Britain, the Office for Nuclear Regulation (ONR), the Environment Agency (EA) and Natural Resources Wales (NRW), jointly issued a position statement on design assessment and a new joint policy on leveraging international judgements and assessments.

This briefing explores the key features of US Part 53 and the UK's evolving design assessment and licensing frameworks, highlighting how regulators on both sides of the Atlantic are reshaping their approaches to support and accelerate the deployment of advanced nuclear technologies.
 

Risk-informed, performance-based approach

Part 53 represents a move away from prescriptive, technology-specific requirements, focusing instead on outcomes and safety goals rather than detailed design rules and specifications. As a result, applicants have the flexibility to demonstrate safety through risk assessments and performance metrics, potentially simplifying the application documentation that needs to be submitted. This approach is similar in some respects to the outcomes-based (long-standing) approach to regulation adopted by the ONR, the UK nuclear regulator.
 

Technology neutrality

The new US framework applies to a wide range of advanced reactors (e.g. small modular reactors, microreactors, non-light water reactors) so applicants are not required to tailor submissions to outdated or irrelevant requirements. Part 53 is drafted with the broader term “commercial nuclear plant” rather than “advanced nuclear reactor” and the new framework is available for any reactor technology, size, and end use.

This technology neutral approach will keep the field open to multiple technologies, avoiding a narrowing down of the technology options and supporting further future development. The fact that Part 53 is technology-inclusive and does not favour any specific technology or design aims to ensure that the market remains open and competitive, which in turn should help drive technology improvements and efficiencies.
  

Streamlined licensing process

Under Part 53, application and review procedures are simplified with applicants offered flexibility as to how they meet the safety requirements. This approach is expected to encourage innovation and reduce the regulatory burden on new applicants. It should be particularly helpful in the context of new advanced reactors which currently have a limited operating history.
 

Safety and security integration

Part 53 nevertheless continues to set high standards for safety and security, with an approach that encourages the integration of safety and security requirements into the design itself. Applicants can, however, organise their safety case and supporting documentation in a way that best demonstrates compliance with performance objectives. Interestingly, Part 53 permits the use of generally accepted codes and standards, which, where appropriate, could potentially enable the use of non-nuclear codes and standards for non-safety-related aspects of advanced nuclear reactor designs, to potentially reduce costs.

Applicants can also use probabilistic risk assessments, modelling and simulation to support their safety case, reducing the need for extensive deterministic analysis. This again may prove helpful in the context of new technologies with limited operational history. Part 53 omits the requirement to conduct a standalone aircraft impact assessment on the reactor design, a major change that could potentially result in meaningful cost reductions for some advanced reactor developers going forward.
 

Stakeholder engagement

Transparency and public involvement are central to the Part 53 licensing process. Application documents, safety cases, and NRC review materials are made available to the public through the NRC’s online platforms. Stakeholders can track the progress of applications and NRC decisions as they unfold.

During licensing reviews, the NRC will provide formal opportunities for public comment on applications. NRC decisions, including licensing approvals, denials, and safety findings, will be documented and published for public review. The rationale for decisions will be clearly explained, including how public input was considered.
 

Parallel developments in the UK

In parallel, the UK is reshaping its design assessment framework to facilitate the faster rollout of advanced nuclear projects. On 22 May 2026, Great Britain's regulators, the ONR, EA and NRW, published a joint position statement on design assessment, alongside a new joint policy setting out how they draw on international regulatory judgements and assessments. Taking a different approach to the US, this adapts the existing principles-based framework to accommodate advanced reactors, without creating a new dedicated licensing regime for them.
 

The evolving framework for design assessments in Great Britain: Joint position statement

The joint position statement sets out the measures being implemented to improve the design assessment processes and meet the target of completing pre-design certification reactor design assessments within two years. This includes immediate updates to the Generic Design Assessment (GDA), and planned future updates to develop a single integrated reactor assessment framework with updated guidance (bringing together the existing GDA and Early Engagement processes) by Spring 2027, and to review public and stakeholder engagement approaches. This will eventually result in the transition to a single regulatory output, describing the regulators’ joint decision on design acceptability. It should be noted that existing safety, security, safeguards and environment (SSSE) standards will not change.
 

Immediate updates to the Generic Design Assessment

The UK's reactor design assessment framework has shifted to a more flexible model, moving away from the sequential three-step model of Initiation, Fundamental Assessment and Detailed Assessment. The old model (which was also voluntary) assumed developers would typically complete all three steps before formally applying for licences and permits (the site-specific route), and guidance was drafted on that basis.

Under the updated approach, set out in the May position statement, applicants can choose from a range of routes through the regulatory process - full or partial GDA, applying directly through the site-specific licensing route, or a number of hybrid and parallel paths; for example, proceeding to GDA Step 2-level assessment alongside licence preparation, stopping at Step 2 before moving into direct licensing etc. As GDA is voluntary and not a formal requirement of the licensing regime, it can be skipped provided the applicant can demonstrate an equivalent level of design maturity –  regulators will require Step 2-level confidence in the design to grant a site licence and Step 3-level detail before nuclear construction and operation.

+ GDA Step 1: Now a distinct preparatory phase that can run alongside Early Engagement. As it involves no design assessment, it sits outside the regulators' two-year assessment target;

+ GDA Step 2: Design is suitable for deployment, even if not fully detailed. Considered an equivalent standard to that required to grant the nuclear site licence. Applicants must pass a readiness review to enter Step 2, when the two-year assessment target starts to run;

+ GDA Step 3: Fully detailed design stage, also gated by a readiness review. Applicants on either route will need to demonstrate Step 3 equivalence for nuclear construction consent and operational permits.

The framework places greater emphasis on readiness, including stable designs and complete, high-quality documentation at the outset of Steps 2 and 3. It allows continued regulator engagement and ongoing development of the SSSE case between stages rather than strictly sequential progression. This is intended to improve efficiency, reduce duplication and ensure projects are better prepared before formal assessment begins.

The regulators are applying a common standard across GDA and site-specific routes, and plan to publish a single integrated regulatory framework and guidance, bringing together Early Engagement and GDA, by Spring 2027.
   

New operational policy on leveraging international regulators' assessments

A new operational policy sets out the principles the UK regulators will follow when drawing on the work of international counterparts, reducing duplication and making better use of assessments already carried out by trusted nuclear regulatory regimes – including under the Atlantic Partnership and with a broader range of national regulators in established nuclear countries. The policy is particularly relevant to new reactor technologies already reviewed by international regulators. A clear message from the policy is that UK regulators retain regulatory sovereignty and will assess all international material against UK legal and regulatory requirements. Key features are:

+ A more proactive regulator role: UK regulators will engage directly with international counterparts to understand and validate their reviews, rather than relying on the applicant to show how that material meets UK expectations.

+ Repeated use cases: For generic design issues, this could reduce the need for UK-specific SSSE demonstrations where equivalent material has already been accepted by regulators in established regimes.

+ Legal duties unchanged: A site-specific UK SSSE case is still required, and responsibility for demonstrating compliance remains with the applicant.

+ Five guiding principles: Regulatory sovereignty, benchmarking, confidence and accountability, transparency, and information security - are all key.

+ Three-test method: The regulators will apply tests on regulatory information, regulatory equivalence and assessment significance - to decide, on a risk-informed basis, how far another regulator’s work can be used and what due diligence is needed.

This approach is already being applied in practice, and ONR illustrates this in two GDA Step 2 case studies: Holtec SMR-300’s fuel and control rod assemblies, where confirmatory due diligence was sufficient; and the GE Vernova BWRX-300’s diaphragm plate – steel composite modular construction, which ultimately required more extensive due diligence with targeted sampling alongside the other regulators’ work.
 

Key features at a glance: US Part 53 and UK’s updated GDA framework 

 
Redesigning frameworks for the future Although the US and the UK have different nuclear regulatory traditions, they are working towards the same objective: accelerating the deployment of advanced nuclear reactors through early engagement, technology-inclusive assessment, and flexible, proportionate regulation, while maintaining existing high standards of safety and security. That both regulators are moving in this direction at the same time is to be welcomed, and a strong signal of support for the anticipated growth of nuclear. It will be important to follow the practical application of Part 53 and its use by developers and the transition of the UK regime towards a more integrated, streamlined and internationally informed reactor assessment framework. Closer international regulatory alignment and co-ordination will be critical to the future of advanced nuclear.