From the magazine – Nuclear power on ships isn’t new. Pressurised water reactors have operated safely on warships since the 1950s. Nuclear propulsion is typically associated with submarines or icebreakers, not construction vessels or deep-water production systems. Yet, after two years of structured research, engineering assessments and regulatory engagement, our conclusion at Allseas is clear: for large, energy-intensive offshore vessels operating far from shore, nuclear power is not just a future possibility – it is the only scalable, reliable and economically viable route to full decarbonisation.
This article originally appeared in SWZ|Maritime’s December 2025 Fuel transition special. It was written by Stephanie Heerema, Project Manager Nuclear Developments at Allseas.
Allseas‘ ambition is straightforward: develop a new class of marine-compatible small modular reactor (SMR) and deploy the first system within five years, beginning with land applications. Offshore integration will follow two years later as regulations mature.
Also read: Study: Allseas’ SMRs could power 700 ships
Why we started: an unavoidable energy problem
The maritime and offshore sectors are at a critical crossroads, grappling with growing energy demand, rising operational costs and increasingly strict environmental regulations. Energy intensive offshore vessels and commercial shipping require continuous power loads that conventional fuels increasingly struggle to meet. On our own deep-sea mineral production vessel Hidden Gem, for example, the subsea compressor spread alone draws 20 MW of continuous power – an energy load equivalent to 10,000 households. Supplying that with conventional fuels would require a bunkering vessel every two weeks, adding cost, operational risk and emissions.
We have investigated the role alternative fuels can play. Biofuel pilots across our operations delivered up to 25 per cent CO2 reduction without significant engine modification. However, cost premiums remain high and widespread adoption depends on volatile policy frameworks such as the EU Emissions Trading System (ETS), expanded to cover maritime transport in 2024. For us, biofuels serve as a bridging option, not a long-term solution.
Energy-dense fuels such as ammonia and methanol are well suited for smaller vessels with flexible operating profiles. But for large offshore construction assets, they fall short in both energy density and global supply. Producing green ammonia at a scale sufficient for global shipping would require almost three times the EU’s 2022 total energy generation. Hydrogen faces the same bottlenecks.
Renewables cannot meet the load either. Hidden Gem would require 75,000 solar panels, a dedicated 20-MW offshore wind turbine, or more than 3000 large-scale battery packs just to run its compressor system. For vessels with continuous power demands above 10-15 MW, nuclear power is the only realistic route to deep decarbonisation.
Why nuclear, and why now?
Commercial shipping contributes nearly three per cent of global CO2 emissions. Meeting the International Maritime Organization’s (IMO) targets – reduction in emissions of at least twenty per cent by 2030, seventy per cent by 2040 and net-zero emissions by 2050 – requires transformative, not incremental, change. Nuclear energy stands out for its power density, a measurement of the power a system can handle or produce relative to its size or volume. Nuclear energy is by far the most efficient energy source.
Nuclear propulsion at sea is not new; naval reactors have accumulated more than seventy years of safe operational history. What is new is the opportunity to translate that experience into a civilian maritime context, with its distinct requirements for licensing, insurability, port access and international oversight. Modern SMRs make this translation possible. They deliver high power output from compact systems that can be produced in controlled factory conditions, drastically reducing cost and construction complexity.
Selecting the right reactor: why Allseas chose HTGR We worked with a variety of nuclear experts and visited several leading US nuclear institutes to evaluate which reactor technologies could realistically operate at sea. Inherent safety, high technology readiness and compatibility with the confined footprint of an engine room were non-negotiable. We selected the high-temperature gas-cooled reactor (HTGR), a Generation IV design using helium as coolant and graphite as moderator.
HTGRs have several advantages for maritime deployment:
- Passive safety: If temperatures rise, the reactor naturally reduces power without operator action.
- Helium coolant: Chemically inert, does not boil, and avoids phasechange issues.
- High operating temperatures: Up to ~750°C, enabling efficient power conversion.
- Proven technology: Prototypes have existed since the 1960s; modern micro-HTGR programmes are advancing rapidly.
Also read: Allseas and STL Nuclear to fast-track reactor design
The fuel: TRISO as the foundation of safety
Every HTGR relies on TRISO fuel – sub-millimetre uranium particles enclosed in multiple ceramic layers acting as their own pressure vessels. TRISO is regarded as the most robust fuel form ever developed, engineered to retain fission products up to 1600°C. For a moving vessel at sea, this is key. Each particle provides its own containment system, making the fuel inherently tolerant to external shocks or temperature fluctuations. TRISO is the fuel of choice for nextgeneration terrestrial SMRs and gives our design the defence-indepth required for maritime applications.
A reactor at sea must withstand dynamic forces – roll, pitch, heave and yaw – that land-based plants never encounter. Early in our programme, we commissioned motion studies to evaluate the behaviour of the core under vessel motion. We are now conducting further modelling and validation with partners including NRG PALLAS and Delft University of Technology.
Allseas has also formed a partnership with STL Nuclear, a South African reactor technology specialist with decades of HTGR and fuel-cycle experience. The collaboration accelerates design work and strengthens our expertise in core physics, materials, fuel qualification and safety case development.
Responsible waste management is embedded from the start, including strategies for graphite reuse and potential future TRISO fuel reprocessing. In parallel, we are evaluating supercritical CO2 Brayton-cycle turbines as an alternative to steam systems. Their efficiency, compactness and reduced maintenance profile make them highly attractive for marine integration.
Why build a reactor instead of buying one?
We conducted a global evaluation of available SMR designs. None were compatible with maritime requirements. Naval reactors are classified and unavailable for commercial use. Civilian SMRs are optimised for stationary land deployment – too large, too heavy, and designed around a different safety case.
Building our own reactor is therefore the most efficient path. Our 25 MWe/70 MWt HTGR is compact, modular and designed from the outset for marine and industrial deployment. Allseas’ design enables a wider variety of applications than typical SMRs, making it suitable not only for offshore construction vessels, but also for bulk carriers, container ships, tankers and other energy intensive assets.
The power can be varied between at least forty per cent and 100 per cent (10-25 MWe), with a five per cent ramp up or ramp down time per minute, allowing flexible adjustment to the different power needs of diverse vessel types. Factory production will ensure consistent quality, reduce cost and support scalable rollout.
Also read: Allseas’ offshore vessels to sail on nuclear power
The regulatory pathway
Developing a marine SMR is as much a regulatory challenge as a technical one. Port access rules, liability frameworks, classification requirements and insurance models all require modernisation. Momentum is now visible. The Dutch government recognises SMRs as strategically important and supports development through initiatives like NuclearDrive, which aims to standardise regulation for mobile reactors.
At the international level, the International Atomic Energy Agency (IAEA) and IMO have initiated joint discussions to develop licensing principles for nuclear-powered merchant vessels. Classification societies, including Lloyd’s Register, are investing in nuclear standards and certification methodologies. Allseas is currently preparing pre-licensing applications with the Dutch Authority for Nuclear Safety and Radiation Protection (ANVS). Regulatory clarity is improving – slowly, but decisively.
Beyond shipping: broader economic impact
While maritime deployment is our primary objective, the broader industrial demand for compact, resilient and zero-emission heat and power is considerable. Our SMRs are well suited to energy-intensive industrial clusters, refineries, chemical sites, ports, data centres and semiconductor fabrication facilities – sectors where electrification is limited by grid congestion and renewable variability.
An impact study conducted by strategic consultancy firm Roland Berger highlights the national opportunity. Deploying up to 110 Allseas SMRs across the Netherlands could generate € 130 billion in economic value and create up to 40,000 jobs by 2050, while easing grid congestion and enhancing energy security. A further 700 maritime units globally could reduce annual CO2 emissions by 55 million tonnes – around the emissions of 3.5 million Dutch households.
Also read: Allseas to install 500-km pipeline in US Gulf
Roadmap to deployment
Allseas has established a clear five-year development programme. The initial phase focuses on design studies and pre-licensing, followed by prototype development and establishment of a dedicated production facility. Deployment will begin on land around 2030, with the first offshore integrations expected shortly thereafter – potentially delivering the world’s first commercially viable civil maritime SMR by 2032.
The key milestones are:
- 2025-2026: Design studies and start of pre-licencing with ANVS.
- 2027-2028: Basic and detailed design, testing.
- 2029-2030: Building and commissioning.
- From 2030: Initial deployment on land, followed by offshore rollout.
A pioneering mindset
Allseas built its reputation by solving technical challenges once considered impossible – single-lift platform installation and removal, deep-sea mineral collection, and ultra-deepwater pipelaying. Nuclear energy aligns with that legacy.
Much of nuclear engineering revolves around pressure-vessel integrity, welding precision and rigorous inspection. With forty years of experience installing subsea pipelines – effectively long pressure vessels – we bring a world-class track record in welding, materials control and non-destructive testing. The skills, mindset and operational discipline required for nuclear systems are already embedded in our organisation.
We believe nuclear power is the next defining technological shift for the maritime and offshore sectors. The physics support it. The economics support it. For long-range, high-power offshore operations, no other technology offers the combination of safety, scalability, energy density and zero-emission performance required. At Allseas, we are not waiting for others to deliver the solution. We are building it ourselves.
Picture (top): Allseas’ 25 MWe/70 MWt HTGR is compact, modular and designed from the outset for marine and industrial deployment (image Allseas).
