With demonstration projects now underway – including a nuclear-powered LNG tanker and an offshore vessel – the debate is shifting from whether nuclear shipping is possible to how it can be delivered. Here, Jan Emblemsvåg, Professor at the Norwegian University of Science & Technology (NTNU)'s Department of Ocean Operations and Civil Engineering in Ålesund, argues that the key barriers are no longer technical, but regulatory, commercial and political.

Nuclear propulsion is returning to the maritime agenda through projects now taking shape in Norway.

Two demonstration concepts are in development: a nuclear-powered LNG tanker, backed by Knutsen OAS, and a specialised offshore vessel being developed with Island Offshore. This work is supported by a broader research and industrial effort – including the recently completed NuProShip II project – where ship designers, class and operators are examining how small modular reactors can be integrated into real vessel concepts.

The focus is no longer on whether nuclear propulsion is possible but on how it can be implemented – and what stands in the way.

WHY NUCLEAR SHIPPING DID NOT SUCCEED BEFORE
This is not a new idea. When the US Maritime Administration-owned NS Savannah entered service in the 1960s as the world’s first nuclear-powered merchant vessel, nuclear propulsion was widely seen as a future option for commercial shipping.

But then everything stalled. Fossil fuels remained cheaper, and the administrative burden – particularly around port entry – was difficult to manage. Prevailing reactor designs would also have struggled to meet later regulatory requirements. The vessel itself, combining passenger and cargo functions, proved commercially inefficient.

Nuclear propulsion, however, did continue in naval fleets, where governments can absorb costs and risks that are not acceptable in commercial operations.

WHAT HAS CHANGED
Earlier concepts relied on light water reactors (LWRs), including boiling water and pressurised water designs. These operate under high pressure and require large emergency planning zones, which makes them difficult to use in commercial ports. Their association with past accidents has also shaped perception.

Recent work, including the Nuclear Propulsion for Merchant Ships (NuProShip) I and II projects, has focused on Generation IV reactors and small modular reactor (SMR) concepts in the 5–55 MW range.

A structured selection process based on technical and operational criteria identified three reactor types with potential for maritime use:

• Molten Salt Reactors (MSR), suited to large ocean-going cargo vessels
• High-temperature Gas-cooled Reactors (HTGR), with lower output and engine-like performance
• Liquid Metal Fast Reactors (LFR), suited to stationary or floating assets with stable load

There is no single solution for all ship types. Different reactor concepts are likely to be used in different segments.

Work under NuProShip II, led by VARD, includes the development of a concept design for a nuclear-powered offshore construction vessel. The study examines the integration of a helium gas-cooled reactor as the primary power source, including implications for vessel layout, safety and system performance in a DP environment. The project is funded by the Research Council of Norway, reflecting a broader national focus on advancing nuclear propulsion in maritime applications.

SAFETY BY DESIGN
For commercial use, safety must be built into the reactor itself rather than relying on complex active systems.

The selected concepts use passive safety characteristics, allowing the reactor to stabilise or shut down without external intervention under abnormal conditions.

Fuel design is also central. TRISO fuel – made up of uranium particles individually coated in multiple protective ceramic layers – has been prioritised for its ability to withstand very high temperatures and retain fission products under extreme conditions. In practical terms, this means the fuel itself acts as a containment barrier, reducing the potential impact of scenarios such as loss of coolant and limiting the risk of material release or misuse.

FROM TECHNICAL FEASIBILITY TO COMMERCIAL REALITY
The technical challenges are increasingly understood. The focus is now on how these systems perform in real operational contexts.

Projects such as NuProShip II indicate that nuclear-powered offshore vessels are technically achievable under defined assumptions, including integration with dynamic positioning (DP) systems and high-redundancy power architectures.

The economics are also being reassessed. Initial analysis suggests that nuclear propulsion could become cost-competitive with fossil fuels under certain conditions, particularly if production moves from project-based delivery to a manufacturing approach. Scaling production would allow development costs to be spread across multiple units.

THE REAL BARRIER
The main challenges now lie outside engineering.

Nuclear-powered merchant vessels do not fit within a single regulatory framework. They sit between maritime law, nuclear regulation and international agreements.

Work has started at the International Maritime Organization (IMO), and class societies including Lloyd’s Register, DNV and ABS are engaged. However, developing full regulatory frameworks can take decades.

Projects such as NuProShip II also highlight the need for clearer rules, greater industrial experience and broader acceptance. Without this, technical feasibility alone is not enough to enable deployment.

One proposed approach is for countries to establish agreements covering port access, liability and insurance, allowing projects to move forward in advance of a complete global regime.

The International Atomic Energy Agency (IAEA) has stated that safety, security, safeguards and liability issues can be addressed but progress depends on political will.

CONSTRAINED SET OF OPTIONS
Interest in nuclear propulsion is tied to the wider challenge of decarbonising shipping.

Large vessels remain dependent on fossil fuels. Alternative fuels have been proposed but their scalability is uncertain. Replacing current marine fuel consumption with green ammonia, for example, would require a very large share of global energy production capacity.

This limits the number of viable long-term options for deep-sea shipping.

WHAT HAPPENS NEXT
Nuclear propulsion is not yet in commercial use but development is moving forward, with Norway currently at the centre of activity.

Demonstration projects are being defined, vessel concepts are being tested and regulatory work has begun. The work will continue beyond NuProShip II with a new research centre led by NTNU focused on applied and industrialised nuclear technology, supported by the Research Council of Norway and industry partners.

The next phase will depend less on engineering progress and more on how frameworks for operation, liability and acceptance are established.

If these develop in parallel, nuclear propulsion could become a viable option in parts of the shipping market where alternatives are limited.

These questions – spanning technology, regulation, safety and commercial models – will be explored further at the upcoming International Conference on Nuclear Propulsion for Shipping in Ålesund on 9 June, where industry, regulators and researchers will meet to discuss how nuclear propulsion can move from concept into practical application.