I came across a report describing a large marine diesel engine engineered with such a high level of optimization that it achieves significantly lower fuel consumption while delivering approximately 35% more power output. From an engineering standpoint, this represents a major step forward in thermodynamic efficiency and combustion control. However, the broader response often remains underwhelming: incremental improvements, no matter how advanced, are no longer seen as sufficient. A similar pattern can be observed with innovations such as wind-assisted propulsion systems, including advanced sail concepts capable of reducing fuel consumption by up to 20%. While technically sound, these solutions are still perceived by some stakeholders, particularly environmental groups, as insufficiently transformative.
The maritime sector requires a step change rather than incremental optimization. A fundamentally new propulsion paradigm is needed to drastically reduce or eliminate greenhouse gas emissions. In exploring potential solutions, I encountered a development program in which multiple industrial and research partners are collaborating on small modular reactors (SMRs), specifically Generation IV nuclear reactor concepts, for marine propulsion.
Regulatory pressure is increasing. The International Maritime Organization (IMO) of the United Nations has tightened its decarbonization targets. The maritime sector currently accounts for about 3% of global CO2 emissions, driven by the widespread use of heavy fuel oil and other fossil fuels. Nuclear energy offers an alternative due to its extremely high energy density, near-zero operational emissions and ability to provide continuous baseload power. In addition to onboard propulsion, modular nuclear units could be deployed at strategic port locations to supply shore power, thereby reducing emissions from vessels at berth.
The Dutch offshore engineering company Allseas has announced a strategic initiative to deploy nuclear propulsion across its fleet. Allseas specializes in offshore pipeline installation for oil and gas transport. It is the first major maritime contractor to publicly commit to nuclear energy as a primary decarbonization pathway, explicitly favoring it over alternatives such as hydrogen, methanol, or ammonia. At present, most large ocean-going vessels rely on residual fuels, which are among the most carbon-intensive and polluting energy sources in widespread use.
According to the company’s five-year strategic plan, published in 2025, the first vessels equipped with SMRs could become operational within five years. Allseas aims to achieve full operational carbon neutrality by 2050. Projections indicate that by that time, up to 700 SMR units with an electrical output of approximately 25 MW each could be deployed, potentially reducing CO2 emissions by as much as 55 megatons annually. The initiative is being developed in collaboration with Dutch research institutions, including TNO, TU Delft, NRG PALLAS, and the Royal Association of Netherlands Shipowners (KNVR).
From a technical perspective, the proposed SMR design is based on high-temperature gas-cooled reactor (HTGR) technology. Reactor safety is inherently enhanced through the use of TRI-structural ISOtropic (TRISO) fuel particles. Each TRISO particle consists of a uranium dioxide (UO2) kernel encapsulated in multiple concentric layers of pyrolytic carbon and silicon carbide, forming a robust containment system capable of retaining fission products even under extreme conditions. These particles, typically about one millimeter in diameter, are embedded in a graphite matrix to form spherical fuel elements, commonly referred to as “pebbles”, about the size of a tennis ball.
In a pebble-bed reactor configuration, thousands of these fuel spheres are continuously or semi-continuously loaded into a cylindrical reactor core. The reactor operates with a helium gas coolant, which is chemically inert and does not become radioactive under neutron irradiation. The helium is circulated through the core, where it is heated to high temperatures (in the range of 700–900°C). The thermal energy is then transferred via a heat exchanger to a secondary water/steam cycle, producing steam that drives a turbine-generator set. The expected electrical output of a single module is on the order of 25 MW. A key advantage of this approach is modularity. Reactor units can be factory-fabricated, transported and installed either on board vessels or at fixed onshore locations, reducing construction complexity and improving quality control.
Initial deployment is expected to occur in land-based installations, allowing regulatory frameworks and operational experience to mature before offshore implementation. Subsequent integration into Allseas’ fleet and potentially the wider maritime industry would follow. This phased approach aligns with the company’s sustainability targets, a 30% reduction in emissions by 2030 and full carbon neutrality by 2050, as stated by Stephanie Heerema, project manager for nuclear developments at Allseas.
Although nuclear propulsion in maritime applications is often perceived as novel, it has historical precedents. The first nuclear-powered submarine, USS Nautilus, was launched in 1954, demonstrating the feasibility of compact naval reactors. In the civilian domain, the NS Savannah, launched in 1959 under the U.S. “Atoms for Peace” program, was the first nuclear-powered merchant vessel. It utilized a pressurized water reactor (PWR) with a thermal power of approximately 74 MW, translating to around 20 MW of shaft power. While technically successful and exceptionally clean in operation, Savannah was not economically competitive due to high capital costs, complex regulatory requirements, and limited cargo capacity resulting from reactor shielding and safety systems.
Similarly, the Soviet Union developed the nuclear-powered icebreaker Lenin, commissioned in 1959. Unlike Savannah, Lenin proved operationally viable in the harsh Arctic environment, where its ability to operate for extended periods without refueling provided a decisive advantage. It was initially equipped with three OK-150 reactors, later replaced by two more advanced OK-900 units. The vessel demonstrated the strategic and operational benefits of nuclear propulsion, in remote regions where fuel logistics are challenging.
However, both relied on early-generation reactor technologies with low fuel efficiency, higher operational complexity and less advanced safety systems. Generation IV SMRs incorporate passive safety features, improved fuel integrity and simplified system architectures, making them more suitable for commercial deployment.
As a result, shipping companies are increasingly evaluating nuclear propulsion as a long-term solution for deep-sea shipping decarbonization.