Nuclear power in shipping: a reaction to decarbonization

Now, in the 21st century, the use of nuclear power has entered the list of other candidates, such as hydrogen, methanol or ammonia, always with the aim of decarbonizing the maritime transport sector.

As Maurici Hervas, CENIT researcher and PhD student in energy transition at the Port of Barcelona, points out, these alternatives have advantages and disadvantages. In any case, they are not incompatible with each other, as each one has certain characteristics that make them more suitable, depending on the type of goods transported or the distances the ships have to travel without refueling.

“When we talk about energy and transportation, a key concept is energy density. In the case of maritime, the key thing is volumetric density. Weight, while important, is not as restrictive as volume, which can detract from cargo space and affect the business model of shipping lines. Therefore, the interest lies in those fuels or energy sources with high volumetric energy densities,” argues Hervas.

The advantages of nuclear in maritime transport

In this scenario, hydrogen becomes an uninteresting alternative, since it is a very small molecule “and difficult to contain” and requires cryogenic and hermetically sealed tanks to prevent leaks. The same applies to the “greener” versions of methanol and ammonia, since they are based on the hydrogen molecule itself, according to Hervas.

Nuclear energy, on the other hand, presents a much more attractive volumetric density for shipping, in addition to other benefits, thanks to the new generation of reactors:

• No refueling required

Many container ships and oil tankers require systems of up to 50 megawatts, enough energy to power about 50,000 homes. In contrast, today's nuclear-powered submarines and aircraft carriers use highly enriched uranium and light water reactors, allowing them to operate for 30 years or more without refueling.

New generation reactors can perform a similar function using a less enriched uranium fuel that could be used for commercial purposes.

“This would mean a paradigm shift in logistics, as it would not depend on the volatility of fuel prices that impact fleet management, nor on planning its scales according to bunkering needs,” Hervas stresses.

• Pollutes less than other options

According to the International Atomic Energy Agency (IAEA), compared to other sustainable sources of electricity generation, solar energy requires 17 times more material and occupies 46 times more land to produce one unit of power. In fact, nuclear already provides about a quarter of the world's low-carbon electricity.

“It would allow shipping companies to cope with the European regulatory package such as FuelEU Maritime + ReFuelEU, as this measure pools the emissions generated by a fleet as a whole and allows different types of fuels to be combined with the ultimate goal of reducing overall carbon emissions,” argues the new fuels expert.

• It is an energy that promotes circularity

Much of the nuclear waste can be used to produce energy using new-generation nuclear technologies. That is why, says Hervas, the industry does not speak of “nuclear waste”. “The new technology used in fast reactors makes it possible to reuse the fuel and put it to other uses,” he stresses.

The new generation of nuclear reactors, key for transportation

“Most of the reactors currently in use belong to the third generation, while the fourth generation, currently in the research and development phase, is the one that will open up a new field of possibilities,” says Hervas.

One of the keys to this new generation of five types of nuclear reactors is that they use alternative coolants that improve safety over traditional designs.

• Molten salt

It uses uranium dissolved in a liquid mixture of molten fluoride salts to generate heat through a controlled nuclear fission chain reaction in the core. The molten salt acts as a coolant and moderator, maintaining the chain reaction. Molten salt reactors are fueled for life, so they do not need to be refueled.

• Microreactors

A nuclear heat pipe (low-pressure microreactor) is a passive heat transfer device. Uranium is used as fuel to generate heat through a controlled nuclear fission chain reaction in the reactor core.

• Pressurised Water Reactors (PWR) 

This category has been transformed into small modular reactors that could be used on board. They use uranium as fuel to generate heat through a controlled nuclear fission chain reaction. The heat is transferred to the coolant, which in a PWR is usually tap water.

• High-temperature gas reactors (HTGRs)

High-temperature gas reactors are advanced nuclear reactors that use a mixture of fuel types and employ helium gas as a coolant to extract heat for electricity or thermal power generation. They have passive safety systems, such as graphite moderation and ceramic-coated fuel for reliable and safe operation.

• Liquid metal cooled reactors

They use liquid metals as coolants instead of water, which allows for higher operating temperatures and higher thermal efficiency. These reactors are also designed with inherent safety features, as the coolants do not react with air or water, reducing the risk of steam explosions or hydrogen production in the event of a leak.

Hervas highlights passive safety as the most important element of the fourth generation of nuclear reactors. He also stresses that there is no need for nuclear energy experts on board in the event of an incident.

“The fourth generation of smaller reactors explores different technologies that allow these reactors to serve different purposes and that, in addition, will be able to be controlled and managed digitally remotely, according to standards to be set by the IAEA and the International Maritime Organization (IMO),” he adds.