Nuclear-Powered Ships From Nautilus to Today
A nuclear-powered ship gets its propulsion from heat produced in a reactor. The first was the submarine USS Nautilus, which went to sea in 1955.
A nuclear-powered ship or submarine gets its propulsion from heat produced in its own reactor. The first was the submarine USS Nautilus, which went to sea in 1955. More than 160 ships now run on over 200 small reactors, nearly all of them warships, submarines or Russian icebreakers. Only four nuclear ships were ever built to carry commercial cargo.[11]
The Submarine's Air Problem
Nuclear propulsion grew out of a submarine problem. A diesel boat runs on batteries under water, and when they run down it has to come near the surface to take in air and recharge. A reactor burns nothing, so it needs no air. The officer behind the idea was Hyman Rickover. He was born on 27 January 1900 at Maków Mazowiecki in present-day Poland, and his family fled pogroms for New York in 1906 and moved to Chicago two years later. He graduated from the Naval Academy in 1922 and served in submarines from 1929 to 1933.[12]
In 1946 the Navy sent him to the nuclear power work at Oak Ridge, and he became an advocate of nuclear propulsion at sea. His superiors disagreed. In 1947 he went directly to Fleet Admiral Nimitz, the Chief of Naval Operations, who backed the project. Congress authorised construction in July 1951, and President Truman laid the keel at Groton on 14 June 1952. The land prototype reactor, S1W, ran in Idaho in 1953. Mamie Eisenhower launched the ship on 21 January 1954, and she was commissioned on 30 September.[1][12]
On the morning of 17 January 1955, Nautilus under Eugene Wilkinson moved down the Thames River in Connecticut and her signalman sent the escort tug Skylark the message "Underway on nuclear power." On an early run she covered 1,200 nautical miles submerged in under 90 hours. She passed her 60,000th mile on 4 February 1957 and reached the North Pole under the ice on 3 August 1958.[1] She was decommissioned on 3 March 1980 and is now at the submarine museum in Groton.
The plant was not very different from a steamship's. In a pressurised water reactor, water carries the heat of fission from the fuel, a separate circuit makes steam from that heat, and the steam turns a turbine. The reactor stands where the boiler would. Military reactors use highly enriched fuel in a small core, 93% in the case of Nautilus. That fuel lasts a long time: new submarine cores are designed for 30 to 40 years, while Arktika-class icebreakers refuel every 3 to 4 years.[11]
For navies the sums were simple. The United States had 26 nuclear submarines by 1962, with 30 more being built.[13] The carrier Enterprise carried eight reactors. At the Cold War peak in 1989, more than 400 nuclear submarines were in service or under construction. At the end of 2019 the counts were 70 in the United States, 40 in Russia, 19 in China, 10 in Britain, 9 in France and 3 in India.[11] A military budget, however, was something a merchant ship did not have, and that was the problem when the civil trials came.
Savannah, the Atoms for Peace Ship
In 1955 Eisenhower proposed a civil showcase, a nuclear merchant ship for his Atoms for Peace programme. Congress authorised it the next year, and the administration said from the start that the ship would not have to prove commercial viability. NS Savannah was built by New York Shipbuilding at Camden and launched, again by Mamie Eisenhower, on 21 July 1959. She had a slim, yacht-like hull, cabins for 60 passengers and a 74 MW reactor driving two turbines.[2]
She sailed on her first voyage on 20 August 1962 and the problems began at once. The total cost had reached $46.9 million, of which $28.3 million went on the reactor and fuel. Cargo was limited to about 8,500 short tons, and rivals carried several times that. The crew was a third larger than on a comparable ship and needed special training. A pay gap between deck officers and nuclear engineers turned into a strike at Galveston in early 1963, the reactor was shut down, and training a new crew delayed service by almost a year. The fine hull slowed loading of the forward holds, a serious fault as ports mechanised. Australia, New Zealand and Japan kept her out of their ports.[2]
Passenger service ended in 1965 and she went over to cargo alone. She needed about $2 million a year more in subsidy than a similar conventional ship. The government laid her up in 1971, when fuel oil cost $20 a ton. At $80 a ton in 1974 her running costs would have been no higher than a conventional ship's, but she never came back.[2] She lies at Pier 13 of the Canton Marine Terminal in Baltimore. The reactor went to Utah in November 2022, and decommissioning must be finished by 2031.[2]
Otto Hahn, Shut Out of Suez
Germany tried the same with a cargo ship. Planning began in 1960, to gain experience for future nuclear freighters. Otto Hahn was launched at Howaldtswerke in Kiel on 13 June 1964 and completed on 1 October 1968. Her reactor of about 38 MW (the World Nuclear Association gives 36 MW) ran on 1.7 tonnes of low-enriched uranium. She carried phosphate from Morocco and ore from elsewhere, sailing about 650,000 nautical miles on 126 voyages and calling at 33 ports in 22 countries.[3][11]
The problem again was port access. She was refused passage through the Suez Canal and did not get enough harbour permissions, and the World Nuclear Association adds running costs as a reason. In 1979 the reactor came out and a diesel engine went in. She returned in 1983 as the container ship Trophy, changed hands and names several times, and was broken up in Bangladesh in 2009.[3][11]
Mutsu, the Ship That Could Not Come Home
The third ship was Japanese. Mutsu was launched in June 1969 and fuelled in September 1972. Protests at Ōminato pushed the first reactor test out to sea, about 800 km east of Cape Shiriya. She sailed in August 1974 and the reactor went critical on 28 August. Four days later, on 1 September, at only 1.4% power, a flaw in the shielding let neutrons and gamma rays escape. Westinghouse had warned of this risk in a design review, and the design had not been changed.[4]
Exposure was not significant, but protests by fishermen kept her from port for more than 50 days. She returned to Ōminato on 15 October 1974 only on condition that a new home port was found. The shielding was repaired at Sasebo from 1978 to 1982, and the new port of Sekinehama was ready in 1983. Mutsu completed her planned 82,000 km of trials and retired in 1992, after a 25-year programme that cost over 120 billion yen. The reactor came out in 1995, and the hull became the ocean research ship Mirai, which worked until December 2025.[4]
The Exception in the Ice
Nuclear propulsion found a lasting civil role in only one job. After the war the Soviet Union was developing the Northern Sea Route to reach northern resources, and a ship working at full power in ice for days at a time could not return to a distant port for fuel. Lenin was launched in Leningrad in 1957 and started work on Arctic routes in 1959. Her early years were hard. In February 1965 coolant was drained from reactor number two before the fuel was removed. Part of the fuel melted and deformed, and 124 assemblies stuck in the core. A further cooling leak in 1967 led to all three reactors being removed, and two new ones were in place by early 1970. Lenin worked until 1989 and became a museum at Murmansk in 2005.[5]
Six ships of the Arktika class followed, each with two 171 MW reactors. The lead ship became the first surface vessel to reach the North Pole, on 17 August 1977.[6][11] Russia's current Project 22220 ships have two 175 MW RITM-200 reactors and can break 2.8 m of ice. Seven are planned, and Chukotka is scheduled to enter service by the end of 2026. This fleet is what stands behind traffic on the Northern Sea Route.[11]
The fourth commercial ship came from this same world. In 1978 Soviet ministries ordered an ice-strengthened, nuclear-powered barge carrier for Arctic cargo. Sevmorput was delivered to Murmansk Shipping Company on 31 December 1988. After Chernobyl, Far Eastern ports refused her out of fear of radiation, and she did not get into Vladivostok until 13 March 1989. She sat idle for long stretches in the 2000s, returned to service in 2016 and carried material to the Rooppur plant in Bangladesh in 2021. A fire broke out at her Murmansk berth in December 2023. Sources differ on her status: the World Nuclear Association calls her the only nuclear freighter in service, while Wikipedia's 2025 record has her laid up at the Atomflot base.[7][11]
What the Four Ships Had in Common
All four stories catch on the same points. A reactor runs for a long time without refuelling, but building costs and special crews outweigh that. When ports refuse a ship, her routes shrink. Savannah's specialised shore staff and servicing facilities served only one ship, so the whole fixed cost fell on her alone. Insurance is a further problem, since the 1962 Brussels Convention on the liability of nuclear ships never came into force.[13]
New Reactors and an Old Code
The sums have been reopened in recent years. Under net-zero pressure, owners are looking at every fuel from LNG to hydrogen, and that has brought the reactor back onto the table. The current IMO rule, the Code of Safety for Nuclear Merchant Ships in resolution A.491(XII), dates from 1981 and is written around the pressurised water reactor. On 26 June 2025, at MSC 110, the Maritime Safety Committee gave the review of the code to the Sub-Committee on Ship Design and Construction. Meeting from 19 to 23 January 2026, the sub-committee drew up a high-level work plan, under which the revised code and amendments to SOLAS Chapter VIII would be adopted in 2030.[8][9]
The commercial side is busy too. Norway's NuProShip study assessed 99 small reactor developers and picked out three designs by January 2025. China's Jiangnan shipyard showed a molten salt reactor container ship design in December 2023.[11][13] The US Maritime Administration, MARAD, issued a request for information in May 2026, and on 26 August 2026 it signed a cooperation document with Core Power aimed at starting construction of US-flagged nuclear merchant ships in 2028. The document lists ports, crew certification, nuclear fuel, insurance and finance separately.[10][11] Crew and ports are where Savannah and Mutsu got stuck.
Frequently asked questions
What is a nuclear-powered ship?
A nuclear-powered ship or submarine gets its propulsion from heat produced in its own reactor. The first was the submarine USS Nautilus, which went to sea in 1955.
How many nuclear merchant ships have been built?
Four: the American Savannah, the German Otto Hahn, the Japanese Mutsu and the Russian Sevmorput. Icebreakers are not included in that count.
Why did nuclear ships not become common?
Because of building cost, specially trained crews, ports refusing entry and insurance. Those obstacles weigh less on warships and Arctic icebreakers.
What rules apply to nuclear ships today?
The IMO's 1981 code, A.491(XII), still applies. A review began in 2025, with a revised text due for adoption in 2030.
Which countries operate nuclear submarines?
The United States, Russia, China, Britain, France and India. The United States and France also run nuclear aircraft carriers, and Russia runs nuclear icebreakers.
How long does nuclear ship fuel last?
New submarine cores are designed for 30 to 40 years and carrier cores for 50. Russia's Project 22220 icebreakers refuel every 6 to 7 years.
Sources
- Wikipedia. USS Nautilus (SSN-571).
- Wikipedia. NS Savannah.
- Wikipedia. NS Otto Hahn.
- Wikipedia. RV Mirai (the Mutsu period).
- Wikipedia. Lenin (1957 Icebreaker).
- Wikipedia. Arktika-Class Icebreaker.
- Wikipedia. Sevmorput.
- Brookes Bell. IMO Agrees Major Revision of Safety Code for Nuclear-Powered Ships, 15 August 2025.
- AJOT. IMO Advances Plan to Update Regulations for Nuclear Ships, 2 February 2026.
- ENGINE. Core Power and MARAD Aim to Start Construction of Nuclear-Powered Merchant Ships in 2028, 26 August 2026.
- World Nuclear Association. Nuclear-Powered Ships.
- Wikipedia. Hyman G. Rickover.
- Wikipedia. Nuclear Marine Propulsion.
