Nuclear Ships: Harnessing Nuclear Energy for Sustainable Marine Transportation

Nuclear Ships: Large cargo vessels carry almost 80% of the world’s commercial products on their journey.

This implies that the majority of the goods you purchase and the food you consume may have a cost.

This is because the maritime sector is difficult to decarbonize and contributes close to 3% of global carbon emissions.

Is that possible?

History of Nuclear Ships

For over 60 years, nuclear reactors have been used to power military ships in an environmentally friendly manner. As a result, there is increasing interest in utilizing new reactor technologies to significantly reduce the carbon footprint and operational expenses of the marine industry.

It is a fact that non-renewable energy sources are steadily running out at a highly concerning rate due to the growing demands of the world’s rapidly growing population in developing nations.

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The majority of the world’s gross energy consumption is derived from non-renewable sources, which are simply those that come from natural reserves of fossil fuels and other organic components, such as petroleum products like gasoline and diesel or different kinds of natural gases.

Thus, for the past few years, a wide range of industries around the globe have searched for alternatives to traditional energy sources, or what are known as non-renewable resources. These consist of nuclear power, solar, wind, tidal, and hydraulic energy.

These are included in the category of “renewable resources.” While renewable energy sources such as wind, tidal, solar, and hydropower are infinitely and boundlessly available, nuclear power cannot be considered a completely natural form of renewable energy.

Chemical reactions using specific nuclear compounds under particular conditions are the source of nuclear power. Despite being referred to as a “clean source of energy,” nuclear energy cannot be compared to other naturally renewable energy sources for the following reasons:

Furthermore, they cannot be completely considered safe, either in terms of the environment or the process involved in their production. They are costly, and continuous procurement comes at a hefty cost for any kind of process. Finally, they require even more expensive paraphernalia and conditions for exploitation.

Speaking of the environment, it can still be argued to be far cleaner than the previously listed conventional carbon-based renewable energy sources. They are by no means “inexhaustible” or fully renewed, but they are nonetheless quite “abundant.” They are in plentiful supply, which is a critical problem for traditional methods. Therefore, nuclear power can be categorized as a hybrid of non-renewable and renewable energy sources.

The transition of the economic sectors to renewable energy sources also applies to ships. There has been a lot of discussion about the pollution that comes from international shipping traffic over the past few years. The transportation sector is responsible for over 3% of the world’s carbon emissions, and if nothing is done, this percentage is projected to rise alarmingly by 2050.

Nuclear-Powered Ship

Moreover, it is responsible for roughly 10% of sulfur-based pollution and an alarming 20–30% of nitrous pollution globally. The International Maritime Organization (IMO) has been collaborating with statutory entities, political bodies, environmental agencies, and shipping sector stakeholders around the clock to reduce ship emissions worldwide. Its most recent, much-discussed, lofty objective is to reduce ship emissions by a minimum of 40% by the upcoming 2030 and a staggering 70% by 2050.

Thus, over the past few years, several commercial ships have made the switch to nuclear-powered propulsion as a significant step toward reducing emissions and abiding by international regulations without sacrificing revenue or the supply chain. Special purpose and military vessels are joining the assault as well.

Numerous recently constructed vessels are intended to be nuclear-powered, but several older, already-built vessels are also switching from conventional to nuclear propulsion. Some ships, dubbed “hybrid” vessels, are also equipped with a dual propulsion system that combines nuclear and conventional methods.

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The Use of Nuclear Propulsion

Nuclear Propulsion
(Credit: India TV News)

Nuclear ship uses nuclear energy entirely or in part to power it. Utilizing the heat energy produced by specialized nuclear reactors, a nuclear vessel propulsion plant transforms that heat energy into the mechanical and electrical energy needed to rotate its propulsive components, either directly or indirectly, using intermediary electrical motors and generators.

The main distinction between nuclear propulsion and conventional propulsion is where the heat energy is produced. Otherwise, the frameworks are nearly identical. Using conventional methods, heat energy is produced by tapping into the calorific value of energy found in renewable fuel sources like coal or diesel (mostly from older times). On the other hand, nuclear vessels make use of the energy from a nuclear reaction.

So the question is, what is the mechanism of a nuclear reaction? The response is that the same nuclear reaction principle that is applied in other contexts—such as in nuclear power plants or stations—is also applied in the context of vessels.

It should be emphasized that fission is the main nuclear reaction process, even though we do not delve deeply into the chemistry of nuclear power generation and reactions. Technically speaking, this is the opposite of fusion, which is the term used to describe the joining of two or more substances into one.

On the other hand, fission is the breakdown of atoms to create distinct elements, and from a nuclear perspective, the process generates a huge quantity of heat energy. If properly utilized, this released energy index can be extremely helpful in producing a significant amount of power.

It is now necessary to conduct the nuclear reaction in an appropriate setting. Whether a nuclear power station is on land or in a ship, its core component is the nuclear reactor. In a nutshell, a nuclear power plant is a controlled environment with regulated temperature, pressure, and other parameters appropriate for conducting nuclear reactions. Moreover, they are in charge of storing the energy that needs to be transferred to produce electrical energy. Known as the “heart of any nuclear power plant,” nuclear reactors are available for purchase and can be expensive. Therefore, ships use specialized reactors.

Currently, all of the fuel used in nuclear reactions is uranium (U-235), a particular variety of radioactive or nuclear material. While other nuclear materials, such as plutonium, are also occasionally employed, U-235 is still the most popular and widely used. This uranium is often kept in a series of sealed metal tubes called fuel rods or the reactor assembly in a nuclear reactor architecture.

There may be a few hundred or more of these rods, depending on the reactor’s size and production capabilities. Generally speaking, this comprises the reactor’s core. This core assembly is where the primary nuclear reaction starts, happening at a fast and uncontrollable pace. Therefore, they need to be appropriately managed to avoid explosions caused by overheating or uncontrollably high fission reactivity.

The coolant for the fuel assembly, water, is submerged in these fuel rods. With these fuel rods, fission takes place, and the water regulates the heat index generated by the chain reactions. It is crucial to understand at this point that all nuclear events are fundamentally just chain reactions that, if left unchecked, may go on forever.

Similar to conventional methods, the extremely high temperatures that the water absorbs cause it to turn into steam. This steam is then used to generate mechanical energy for operating built-in turbines, which is mostly transformed into electrical energy needed for propulsion and other uses. In certain instances, the propeller assembly can be directly equipped to generate power through direct drive by harnessing the mechanical energy.

Power conversion from mechanical to electrical is frequently accomplished using hybrid turbines or turbo-electric systems. These types of ships are referred to as dual or hybrid nuclear-electric propulsion ships.

To put it briefly, the main parts of any nuclear power plant are:

  • Reactor
  • Steam Generator
  • Coolant Pressurisation system
  • Purification System cooler
  • Turbine
  • Condenser
  • Feed Water Supply system
  • Coolant lines and piping
  • Containment systems

In a nutshell, the two primary types of nuclear reactors in use are:

  1. Reactors for Pressurized Water
  2. Water Reactors at Boil

The feed water in pressurized water reactors is constantly pushed to the core or assembly at a high pressure and constant pace. In essence, this keeps the water from boiling away. This heated water is pumped and directed into a series of water tubes piled into what is called a heat exchanger after being exposed to the nuclear fission process.

Nuclear Power Facility

Nuclear Power Facility
(Credit: Marine time executive)

This exchanger is currently adding water from a different fresh supply source that has already been heated. After being heated, the water boils and turns into steam, which produces mechanical energy for electrical systems like turbines. The heated water inside the tubes is trapped inside the tubes and reheated by recirculating it back to the reactor once it loses heat. This cycle is performed continually as needed.

In boiling water reactors, however, the procedure is comparatively easier. Here, water is continually pulled from a single source directly into the reactor—without the need for a separate heat exchanger—and is boiled off at extremely high temperatures as a result of the fission process. The steam produced is immediately fed into a turbine to produce energy. After that, the residual steam condenses to liquid and is recycled for heating.

Nuclear Power Plant on a Ship

The nuclear reactors found on ships are very different from those found on land. Ship power needs are quite small, but huge terrestrial nuclear power plants must generate thousands of megawatts of electrical power to meet massive power demands over large areas.

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Additionally, a vessel’s hull has a finite volume, therefore the reactor must be contained in certain areas. Therefore, the nuclear power plant within a vessel is significantly smaller. Small Modular Reactors (SMRs), a scaled-down version of reactors, are frequently utilized in vessels. These reactors are made to be more compact and are mostly pressurized.

Additionally, because a reactor is tiny in size, higher-grade nuclear fuel is employed to improve reaction efficiency. Typically, breeds of uranium 235 or 238 with higher concentrations are employed. While some ships replenish their feed water with seawater, others just utilize a small volume of water that is constantly condensed and recycled back.

The strains resulting from critical values of the heating index across a limited area and the reactor’s tiny size necessitate continuous operation throughout the vessel’s life. Thus, great care is taken in the design of these reactors using premium materials to ensure that they can sustain nuclear reaction effects under restricted settings for the duration of the vessels’ service life, in addition to withstanding high-stress levels.

A nuclear reactor design for a vessel should be robust, dependable, small, and, above all, safe. No matter how good the design, the thermal efficiency of a reactor in a vessel is always lower than that of a land-based one because of the smaller space limits.

Benefits And Drawbacks Of A Nuclear-Powered Ship

There are always two sides to a coin, as they say. Thus, the following are possible benefits and drawbacks of a nuclear-powered ship:


  • They require almost no refueling and are thus very cost-effective. Usually, the fuel stored in the reactor is sufficient to cater for up to 20-30 years of a vessel’s service life. Also, the amount of fuel to be carried is far less. From an economic standpoint, this is much more advantageous.
  • Due to the high efficiency of the reactions, the performance and propulsive efficiency are higher than conventional means. So, these vessels have larger speeds and far lower emissions levels.
  • Nuclear reactions require no influx of free air for combustion. They are advantageous in freezing climates, especially for submarines that frequently do not need to go above water levels to air. In ice-class vessels and submarines, nuclear propulsion also has the upper hand for powering through ice covers.
  • Low emission levels, as discussed above,


  • Hazards and risks associated with nuclear phenomena.
  • High costs of installation and maintenance.
  • Corrosion, high degrees of stress, vibration, and other problems associated with the reactors.

But since its introduction more than fifty years ago, more ships have gone nuclear. The bulk of defense submarines in use today are nuclear-powered. Following the United States and Russia in the lead, nations such as China, India, and the United Kingdom are also choosing nuclear-powered vessels and submarines. One may argue that there will be a significant increase in the number of nuclear warships in the future.

There is ongoing research and development

To investigate maritime shipping applications, DOE is funding many industry and academic projects. One such project involves the American Bureau of Shipping (ABS), which is working with the National Reactor Innovation Center (NRIC) to investigate and showcase new reactor technologies for commercial shipping.

Project teams from universities are also investigating the possibilities of floating reactors and modeling, designing, and assessing the application of advanced reactors in nuclear-powered ships.

Although research and development are being conducted, several regulatory obstacles must be removed before nuclear power is extensively used in the marine sector.

To facilitate the demonstration of cutting-edge reactor technologies in the marine industry, NRIC assisted in the formation of the Marine Nuclear Application Group, which brings together specialists from the maritime and nuclear energy industries.

Idaho National Laboratory is in charge of the national DOE program NRIC, which promotes the creation and testing of cutting-edge reactor systems.

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