Are small nuclear reactors on yachts possible or a pipe dream?

More than 60 years after the concept was first introduced, nuclear reactors have re-entered the sustainable superyachting conversation. While diesel-electric systems and alternative fuels are often touted as the future of yacht propulsion, could a nuclear-powered superyacht be the answer to long-range, zero-emission cruising? BOAT explores.

Imagine running speeds of 20 knots-plus with glacial air-conditioning, all without adding a bubble of CO2 to the atmosphere. Refuel once a decade, and forget the engine room – you can use that space for something much more fun. This is the promise held out by nuclear-powered yachting.

One or two technical and regulatory hurdles may stand in the way of that bright future, however, but let’s get one thing straight: nuclear at sea is nothing new. “More than 700 reactors are deployed in marine, considerably more than on land,” says Mark Tipping, global power-to-X director at Lloyd’s Register (LR). “It’s easy to fall into the trap of viewing nuclear as novel, but it isn’t. This is an evolution.”

There are submarines and aircraft carriers, but also icebreakers and civilian ships. The US even bankrolled the development of the nuclear cargo ship NS Savannah in the 1950s. With half her $47 million cost at the time (£430 million in today’s money) sunk into the reactor system, she was expensive to run and limited in the ports she could visit, so she was decommissioned after a decade.

A silver bullet?

Times are changing, however. Nuclear has become a hot topic in maritime industry forums. “Nuclear propulsion could provide immense value for the maritime sector in its decarbonisation journey, allowing for emissions-free vessels with longer life cycles, which require minimal refuelling infrastructure, or in best-case scenarios limit the need entirely,” says Tipping.

The International Maritime Organization (IMO) has mandated a 40 per cent reduction in shipping’s carbon intensity by 2030 to reach net zero by 2050. Although it doesn’t directly target yachts, there is clear pressure to evolve in the leisure sector. Moreover, alternative fuels such as methanol, ammonia and hydrogen face their own headwinds. Nuclear has the potential to cut through it all.

However, the shipyards at the sharp end of building superyachts are not so bullish. Feadship, no stranger to innovation, says reactors make little sense. The Dutch shipbuilder says that the concrete shielding for the core alone could double the yacht’s weight. And although developers such as HolosGen disagree, they admit that it would take a feasibility study on a specific yacht to be precise about weight.

Feadship also believes that the days and weeks in port or at anchor make deeply inefficient use of the reactor’s power. “Yes, a nuclear-powered yacht will be technically feasible sometime in the future,” says product engineer Ernesto La Colla, “but why integrate a micro modular reactor with an average onboard load of about 10 per cent, when you can put it to better use on shore, making green fuel like methanol for multiple yachts at maximum power?”

Lürssen has also conducted initial studies for a nuclear-powered yacht, but sales director Michael Breman says it is still too much of a stretch. “We’re keeping an eye on it, but it’s too far in the future because of social acceptance,” he says. “I’m talking to clients who have this very high on their radar, but they know it’s on the other side of the fence.”

Still, the circumstances and technology are evolving, and fast.

Plummeting costs

As NS Savannah showed 60 years ago, dropping in a nuclear reactor is not cheap. However, great strides have been taken in recent years to miniaturise and industrialise the technology. It is now possible to create an efficient microreactor that generates just a few megawatts, all in the footprint of a single six-metre container.

Nuclear entrepreneurship is alive in the US, where generous funding has incubated dozens of startups. Among them, HolosGen has developed plans for a high-pressure prototype resembling a jet engine, which generates electricity rather than heat. “It is a sleek cylindrical shape with two hemispherical heads welded on,” explains CEO Claudio Filippone. “With compact dimensions, it can be inserted vertically or horizontally. If you develop a hatch on the vessel, you can slide it in, like a battery on a TV remote control.”

Today’s smaller, mobile reactors are much cheaper, and a financing model akin to leasing can spare owners the high upfront investment. “Then you don’t have to own or operate the nuclear reactor; you lease scalable modules,” says Øyvind Kamsvåg, chief designer at Ulstein. “When you build a ship, you will install the energy required over the lifetime of that vessel. You have to look at energy from a different perspective.”

This approach saves the owner from becoming a nuclear operator or from providing guarantees about managing the spent fuel safely. The industry is looking at a model where all the costs of the nuclear plant – from the engineer to insurance and the decommissioning costs – are all covered by a monthly leasing payment.

“The theoretical cost for this technology and the price per kilowatt-hour is competitive with diesel generators producing electricity,” says Kamsvåg, “but only if you use the energy that the reactor can produce. If the superyacht is on the quayside a lot then it will be more expensive. Economies are based on how much you use it.”

Explorer yachts and large vessels that spend extended time off-grid are stronger candidates for nuclear. The yacht (and for now only the largest ones) could become a power plant by plugging into the shore supply and pumping electricity into the grid. For remote communities in the Pacific or high latitudes, this could be a huge boon.

Rebranding the image

The chief problem with nuclear, however, is security. The consequences of something going wrong with nuclear fission are seared into the ruins of Hiroshima and Chernobyl. And if the danger of radioactivity escaping is one issue, the possibility that nuclear fuel could fall into the hands of malicious actors is another.

The voices raised today in support of nuclear power at sea are quick to play down the risks of both scenarios. They say the new wave of small modular reactors (SMRs) has little in common with the early designs associated with accidents. Today’s so-called fourth-generation reactors are passive, designed to shut down using the laws of physics, not complex controls.

“When it heats up, the reactor cools itself down because the reaction becomes less effective at higher temperatures,” Sytske de Groot, head naval architect at Allseas, says of the design her company is exploring for its fleet of pipeline and wind turbine installers. “The reaction can never exceed the melting temperature of the fuel or the material that contains it. This reactor can never melt or explode, and no radioactive materials can dissolve in the water.”

Nuclear fuel has undergone huge safety leaps as well. Instead of using highly enriched uranium that creates weapons-grade plutonium as a waste product, some SMRs use ultra-robust pellets called TRISO particles. They make the fuel nearly impossible to extract and weaponise and keep the radioactive products locked up safely. Others run on a mixture of salt and thorium, which is more abundant and equally difficult to divert.

Some want to rename nuclear power used in propulsion to dissociate it from the catastrophes of the past. “That is not the kind of technology we’re now using and not the type of risk we’re talking about,” says Jo Assael, yachts commercial director at International Registries. “We almost need a rebrand – for it not to be called nuclear; to convey something positive. Even the term ‘reactor’ is loaded.”

Setting new rules

Regulations must also adapt before nuclear-powered ships become a reality. The challenge is manifold: innovative microreactors must be approved; class societies have to agree on the engineering around them; flag states on safety and training standards for the crew; and finally, IMO members must update their rules to allow nuclear ships into their waters.

What are the prospects for rapid progress? Well, with the UK only recently having enacted the nuclear rules contained in Chapter VIII of the 1974 SOLAS Convention, you might be forgiven for snorting in derision, but that could be a mistake because regulators across the globe are picking up the pace. “The early 2030s are a feasible target for the first nuclear-powered vessels from the regulatory side, which is the bottleneck,” de Groot of Allseas says.

Countries such as the US are already well versed in funding and regulating nuclear innovation with a huge domestic industry and a large nuclear fleet. “In reality, a lot of regulatory and international work has been already done with the commercial nuclear-powered ship Savannah in the late 1950s,” says Filippone of HolosGen. “Nothing is simple, but we do not start from zero here.”

Countries are free to make bilateral agreements, but globally progress is happening with the IMO co-ordinating the issue from one end, and the International Atomic Energy Agency limbering up at the other. It has convened a programme called the Atomic Technology Licensed for Applications at Sea (ATLAS) to bridge the gap between these two regulators.

Private companies are also involved via the non-profit Nuclear Energy Maritime Organization (NEMO). Its members are a cross-section of the industry from classification societies to insurers and reactor builders. Of course, it won’t be a quick fix with so many bodies involved, but at last, the whole chain is pulling in the same direction.

In a sense, the yachting industry doesn’t need to know what goes on inside the nuclear box. Technically, the reactor must resist vibration, temperature variations, immersion and even potential attacks. Once domestic regulators have signed off on its features, from the operator’s point of view, it will just be a big boiler.

The job for yachting specialists will be to figure out how the heat is transformed into electricity, and how that electricity is distributed around the boat. Numerous companies are working on implementing this on commercial ships, from class societies to specialist integrators like Core Power in the UK and America’s Ultra Safe Nuclear, whose Pylon reactor is being developed for deployment in space.

Risk management

Insurance is another key issue. Current global rules date back to the 1962 Brussels Convention so they could use some updating to reflect newer, safer nuclear technologies. Without it, no port or harbour would be willing to accept the risk of having a nuclear-powered ship dock. It’s not clear who will shoulder the liabilities here, but one theory is that the P&I clubs who cover 90 per cent of global tonnage could step in as part of their mandate to cover open-ended marine risk.

An alternative idea is that motivated owners will provide coverage themselves. “We have been approached by individuals that would like to investigate a ship for themselves that could be powered by nuclear,” says Kamsvåg at Ulstein. “On asking them about insurance, they said they would set up their own insurance company.”

Crew training touches on all these issues. No one believes nuclear scientists will run the boats. “The training of (the) crew is likely to be more onerous but will probably not require detailed knowledge of nuclear fission power generation,” says Engel-Jan de Boer of LR.

“What we just don’t know yet is how much space we will gain from putting nuclear on board and whether we’ll lose it all to safety measures and extra crew,” says Assael. “There are more questions than answers.”

The answers to these questions and more will start to come as interest in nuclear boats helps release funding. You might expect faster progress from the behemoths of the shipping world that are up against net-zero mandates, but it might be up to an innovative billionaire to get the yachting sector there first.

“The philanthropic owner of a superyacht may well be one of the first adopters of this tech,” says Tom Walters, a partner with shipping law firm HFW. “You’ve kind of seen it with Bill Gates and his company TerraPower, looking at SMRs to power their data centres to meet their own net-zero criteria.”

While the opinion is split on the future of nuclear in the maritime world, and the hurdles are many, from public perception, to training, energy cost (based on hours at sea) to regulations, it’s evolving fast and a space worth watching.