Nuclear power took a notable step into the centre of the maritime energy debate during day two of Propulsion and Future Fuels
Nuclear power took a notable step into the centre of the maritime energy debate during day two of Propulsion and Future Fuels, where Jez Sims, principal nuclear authority for marine and offshore at Lloyd’s Register, outlined how emerging reactor technologies could reshape shipping’s decarbonisation trajectory.
Speaking to delegates, Sims argued that next-generation nuclear is no longer a distant prospect but a technically feasible and potentially commercially competitive marine fuel—provided regulation, safety assurance and industrial scale can be aligned.
Sims began by setting out the technologies under consideration. Several Generation IV reactor types are now being explored for maritime use, including molten salt reactors, lead-fast reactors and high-temperature gas reactors. These designs, already under development in the land-based nuclear sector, offer passive safety features and accident-tolerant fuels not available in earlier generations. Companies such as Allseas have already declared plans to design and manufacture high-temperature gas reactors for marine applications, signalling growing commercial interest.
The argument for nuclear is rooted in energy density. According to Sims, nuclear contains around 1.8 million times the energy of heavy fuel oil. Where alternative fuels such as ammonia or methanol impose penalties in terms of tank volume, cargo capacity and more frequent bunkering, a nuclear-powered vessel could operate for years between refuelling intervals. Depending on the reactor type and operating profile, refuelling cycles may range from three to seven years, extending further for systems with online refuelling capability. Eliminating conventional bunkering, increasing cargo space and generating carbon-free power en route, Sims said, fundamentally change the economics and operating model of shipping.
For a sense of scale, Sims referenced a newly published Lloyd’s Register study conducted with Seaspan, assessing a 15,000 TEU container ship. Over a 25-year life, a nuclear-powered version could generate operational benefits equivalent to roughly $68 million per year, mainly from avoided fuel expenditure and higher service speeds. With nuclear propulsion removing the need for slow steaming as a means of compliance, ships could return to higher transit speeds with zero emissions during operation. Design studies indicate that removing fuel tanks and reducing engineering space requirements could yield around a 10 per cent increase in cargo capacity on a like-for-like hull.
Regulatory lan dscape
A crucial part of the discussion centred on how these systems would be deployed and licensed. Today’s nuclear regulatory landscape is built around fixed installations, with rigorous site-specific licensing before construction. For maritime use, Sims envisages a move towards product-based licensing, where a reactor manufacturer designs a
standardised unit that is licensed once, type approved and then produced at scale. Lloyd’s Register has already tested this concept through work with Deployable Energy, which has developed a 2 MW electric microreactor designed as a diesel generator replacement. The proposal is for such units to be licensed independently of their final installation, enabling later integration into barges or ships under a defined framework.
Operational models would vary. Some owners may choose to own and operate the reactor themselves, while others may purchase the unit but contract the developer to operate and maintain it—similar to the service agreements used in aviation for gas turbines. A third option would mirror Russia’s floating nuclear power plant model, with the operator effectively buying electricity rather than the asset.
However, progress depends heavily on regulatory modernisation. The current framework, including SOLAS Chapter 8 and the A491 Code for nuclear merchant vessels, dates back to the late 1970s and early 1980s and is no longer fit for purpose. Work is now under way at the IMO, with proposals from the Republic of Korea, the United States and others to update these instruments, with discussions scheduled to progress at STC 12 in early 2026. Lloyd’s Register is also collaborating with the IAEA through Project Atlas, which aims to develop an international pathway for licensing maritime nuclear reactors.
Port access and security were another significant theme. The industry must establish how nuclear-powered ships will enter ports, how safety and safeguarding requirements will be met, and how risks such as piracy or collision will be handled. Sims noted that work is ongoing with a number of ports and organisations including the Nuclear Energy Maritime Organisation and the IAEA to modernise the outdated port guide. Harmonised certification—effectively a nuclear equivalent of existing maritime safety documents—may ultimately allow port states to verify compliance quickly and consistently.
On safety, Sims acknowledged the legacy of nuclear accidents but emphasised that modern Generation IV reactors incorporate passive safety systems, accident-tolerant fuels and designs that cannot rely on active cooling systems in the way Fukushima did. On waste, he highlighted that fast-spectrum reactors can use today’s spent fuel as tomorrow’s feedstock, potentially transforming waste from a liability into a resource. Collision protection, he argued, is an engineering challenge that the maritime sector is already well equipped to address.
In closing, Sims reiterated that nuclear is technically viable and could become a significant part of shipping’s future energy mix. For that to happen, however, three prerequisites must be met: successful demonstration projects, the scaling of supply chains and manufacturing capacity, and the harmonisation of international and national regulatory frameworks. If these conditions are achieved, Lloyd’s Register believes nuclear could become both a net-zero and cost-competitive marine energy
