The Nuclear Container Ship

The Engineering of the ABS-approved 15,000 TEU design, and what 25 knots would change in the liner trade 

Frontier | Winston 

 

 

On July 16, the American Bureau of Shipping granted approval in principle to the design of a container ship with no fuel tanks and no funnel. Two molten salt reactors sit at the middle of the hull, where wave loads and collision risk are lowest, powering a 15,000 TEU vessel sized for the Panama Canal’s Neopanamax locks and a service speed of 25 knots. Behind it is a Korean consortium: the Korea Atomic Energy Research Institute developed the reactor, the Korea Research Institute of Ships and Ocean Engineering drew the ship, and Samsung Heavy Industries would build it.

Frontier reported the approval on X. This article looks at the ship’s design and the numbers behind it. Running a container ship at 25 knots affects how many ships a service needs and how long cargo stays at sea.

Approval in principle is the first formal step in ship classification. It confirms that a new idea meets class rules at the concept stage, before moving on to detailed design and safety checks. Five weeks earlier, Lloyd’s Register approved the same reactor type for a 7,000-unit car carrier made with HD Hyundai. So, two classification groups reviewed Korean molten salt ship designs in one summer.

The reactor is named MARINA. Details like its output, salt chemistry, and core lifespan have not been shared yet, but the group has released the ship’s design. The two reactors run at a steady rate, while an energy storage system takes in extra power and helps during maneuvers. The ship’s propellers and electrical systems use power from this storage. The living quarters were placed based on both radiation shielding and bridge visibility. Before choosing the reactor’s location, KRISO tested a scale model of the hull in its ocean basin to see how the ship moves at sea. They then designed the reactor layout using this data.

Seven decades of reactors at sea

NS Savannah, the American demonstration ship that entered service in 1962, ran a Babcock & Wilcox pressurized water reactor rated at 74 megawatts thermal. Over her career she sailed 450,000 nautical miles on about 74 kilograms of uranium, the energy equivalent of some 29 million gallons of fuel oil. When she was refueled in 1968 after 350,000 miles, the yard replaced four of her 32 fuel assemblies and rearranged the rest. Her operator called her the most reliable ship in its fleet.

Germany’s Otto Hahn, which started service in 1968, improved the ship’s layout in a way that is still important today. Its FDR reactor was the first integral pressurized water reactor at sea, with the steam generator inside the reactor vessel, so there was no need for an external primary loop. The ship traveled 650,000 nautical miles in ten years and made 126 voyages. Its first core lasted 250,000 miles using 1.7 tonnes of low-enriched uranium. Modern integral small modular reactors, like the RITM-200, use this same setup.

Russia has the most experience, with about 400 reactor-years on Arctic civilian ships, according to Rosatom and the World Nuclear Association. The current RITM-200 is an integral pressurized water reactor that produces 55 megawatts of electricity. It is small enough that two can fit inside an icebreaker hull and can run for about seven years between refuelings, using fuel enriched to just under 20 percent. Four Project 22220 icebreakers now use pairs of RITM-200 reactors, with three more being built. Automation has also reduced crew sizes from about 130 on the older Arktika class to 53.

Cargo has its own precedent: Sevmorput, a Soviet-built carrier commissioned in 1988, ran a 135 megawatt thermal KLT-40 for 35 years and needed only two refuelings in her career.

Propulsion reactors at sea are a proven engineering lineage. The open questions live in the reactor type the Koreans have chosen and in the trade they want to run it in.

What the salt changes

A pressurized water reactor keeps its main circuit at about 155 bar, which stops the water from boiling at 300 degrees Celsius. This high pressure is why marine nuclear systems need heavy, expensive parts like a forged vessel, large containment for possible steam releases, and detailed collision analysis to protect them.

 

 

A molten salt reactor works at nearly normal air pressure. The fuel salt boils at over 1,400 degrees Celsius, but the core runs at 600 to 700, so there is no stored pressure energy to worry about. If the vessel is damaged, the salt drains out, cools, and hardens into a solid block, trapping the fission products inside. For ships that need to survive groundings and collisions, not having stored pressure energy changes the safety challenge completely.

Since the fuel is mixed into the coolant, there are no fuel assemblies, refueling machines, or spent fuel pools on board. KAERI says these cores are built to run for long periods without needing new fuel. The Russian fleet shows what this replaces: all Russian civilian marine reactors are refueled at a special base in Murmansk, using dedicated service ships and trained crews. With a sealed core, none of that extra infrastructure is needed.

The way the reactor is controlled comes from its physics. Molten salt cores have a strong negative temperature effect: when the propeller needs more power and the salt comes back cooler, the reactor becomes more active to meet the demand. When less power is needed, the core slows itself down. This means power output matches the ship’s needs automatically, which is useful since ship loads change with sea conditions.

The remaining work is specific, and much of it is documented. Oak Ridge’s Molten Salt Reactor Experiment ran for over 13,000 full-power hours from 1965 to 1969 and identified several problems: the nickel alloy holding the salt developed shallow cracks from tellurium, tritium leaked through hot metal, and the off-gas system for xenon and krypton needed constant engineering. Later work at Oak Ridge solved the cracking with a niobium-modified alloy and better chemical control of the salt. China’s TMSR-LF1, a 2 megawatt molten salt reactor running in Gansu since 2023, is now providing the first new liquid-fuel reactor data in fifty years, including the first in-reactor conversion of thorium to uranium-233, announced in November 2025.

The truly new challenge is at sea. A liquid core has a free surface, and how it behaves during rolling, pitching, and slamming has only been studied in simulations so far, since no liquid-fuel reactor has ever sailed. KRISO’s basin tests are the first real data on how a molten salt ship moves, starting to fill this knowledge gap.