The idea of nuclear-powered shipping is gaining renewed attention as engineers and policymakers explore whether fourth-generation reactors could offer a path to decarbonising maritime transport. At a recent meeting on Nuclear Power for Shipping at the Technical University of Norway (NTNU), optimism was high among proponents of the technology, particularly around small modular reactors (SMRs), with discussions often framing political oversight as a barrier rather than a safeguard.
Jan Emblemsvåg, professor and organiser of the event, argued that engineering progress could be slowed by political interference, reflecting a broader sentiment among some participants that technical development should remain largely insulated from policymaking. The overall tone of the conference leaned strongly toward confidence in nuclear propulsion for ships, with limited discussion of constraints beyond safety acknowledgements.
However, this optimism is sharply contested by nuclear safety specialists who argue that many of the core claims behind SMR technology remain unproven — especially in a maritime environment.
Claims versus technical reality
Dr Edwin Lyman, Director of Nuclear Power Safety at the Union of Concerned Scientists, challenges the narrative that SMRs represent a breakthrough for safe, economical and scalable nuclear power. His April 2024 paper, “Five Things the ‘Nuclear Bros’ Don’t Want You to Know About Small Modular Reactors,” directly addresses the claims frequently made in favour of SMRs: lower cost, higher safety, reduced waste, improved reliability, and greater efficiency.
According to Lyman, none of these claims have been demonstrated in practice. He argues that while SMRs are smaller, this does not automatically translate into lower costs per kilowatt-hour once capital expenditure, maintenance, fuel and operational costs are included. He also cites a University of Cambridge engineering study suggesting that cost reductions from mass production would likely not exceed 30%, far below the 80% reductions sometimes claimed by proponents.
Safety concerns amplified at sea
A central argument for SMRs is that their smaller size and reduced heat output make them inherently safer. Lyman disputes this, noting that passive safety systems may fail under extreme environmental conditions such as earthquakes, flooding or wildfires.
In a maritime context, he argues, these risks are amplified rather than reduced. “I would not be comfortable with deploying SMRs on ships,” he said, highlighting unresolved challenges in fluid dynamics, heat transfer and system stability in a moving marine environment. He stressed that none of these reactors have been tested either on land or at sea.
More concerning still, certain reactor types such as molten salt reactors could generate tritium, a radioactive isotope of hydrogen, which could disperse beyond containment systems and pose risks to crew and cargo. Early experimental solutions, such as charcoal absorption systems, were eventually abandoned, with contaminated materials requiring nuclear waste disposal.
The unresolved issue of nuclear waste
Waste management remains one of the most controversial aspects of nuclear energy deployment at sea. While conference discussions at NTNU reportedly downplayed disposal costs as minimal, Lyman argues the issue is far from resolved.
He points out that radioactive waste management has remained an unsolved global challenge for decades, despite repeated promises from the nuclear industry. Finland’s Onkalo repository remains the only advanced example of long-term geological storage, designed to contain 6,500 tonnes of spent fuel at depths of 400–450 metres, with permanent sealing planned after 100 years. No comparable systems exist elsewhere.
For shipping applications, Lyman warns that no credible waste management framework currently exists. Any company deploying nuclear-powered vessels would require a fully developed, licensed long-term disposal programme — something he considers unrealistic under current conditions. He also notes that certain fuels, such as TRISO, could produce up to ten times more waste than conventional reactors.
Even interim storage solutions, such as cooling spent fuel in water pools before dry storage, involve decades of monitoring and long-term financial liability, often ultimately transferred to governments and taxpayers.
Regulatory gaps and Untested technologies Apart from safety and waste, a key barrier is the lack of a regulatory framework for shipboard SMRs. Lyman points out that no modern SMR design has ever been fully constructed and tested under real operating conditions, and that existing programmes are still confined to experimental settings rather than operating power systems.
But he also warns that the push to accelerate development schedules might compromise engineering integrity, especially for complex systems such as thermal hydraulics and power conversion. “You go down that path, you increase the risk of failure, you don’t decrease it,” he says.
Another complication is the fuel supply. High-assay low-enriched uranium (HALEU), required for many SMR designs, demands more intensive uranium mining processes, which themselves carry environmental and human health impacts. Historical data cited in the discussion indicates thousands of uranium miners have suffered fatal occupational diseases linked to radiation exposure.
A technology still searching for a pathway
Despite industry enthusiasm and political interest in decarbonisation solutions for shipping, Lyman argues that there is currently no viable pathway to deploy SMRs safely in an international maritime context. He highlights the absence of both technical validation and global regulatory consensus, particularly regarding safety, security and non-proliferation controls.
Existing SMR developers, he notes, are under pressure to secure funding in a competitive market, which may encourage overly optimistic claims about readiness and performance. In his view, this competition risks amplifying expectations that are not grounded in operational reality.
Contrary to arguments that political interference is holding back progress, Lyman suggests the opposite: that large-scale government involvement and strict regulatory frameworks are essential prerequisites for any credible nuclear maritime future.
The debate over nuclear-powered shipping remains sharply divided. Supporters see SMRs as a possible foundation for maritime decarbonisation, but opponents argue that the fundamental issues of cost, safety, waste management and regulation are not yet solved.
For the time being, nuclear propulsion at sea remains squarely in the realm of technological aspiration versus practical doubt, a notion that continues to attract interest but has not yet gained the proven foundations needed to support commercial application.
