Radioactive Cargo Sinks in the North Sea Summary

  • Last updated on November 10, 2022

When the Mont Louis, a small French coastal vessel carrying uranium hexafluoride, a mildly radioactive material, collided with a German ferry and sank, the accident highlighted the dangers of transporting such material, although no radioactive material leaked into the sea.

Summary of Event

The Mont Louis was a small, French-registered vessel built by Wartsila Ab of Turku, Finland, in 1972. During the night of August 25, 1984, the Mont Louis was running parallel to the coast of Belgium en route from Dunkirk, France, to Riga, Latvia, in the Soviet Union. Because the ship’s crew size had recently been reduced, the man who should have been standing watch as lookout on the Mont Louis had been assigned to other duties. A West German ferry, the Olau Britannia, Olau Britannia (ship) bound from Flushing, Holland, to Sheerness, England, struck the Mont Louis in its starboard side near the stern. When two ships are on crossing courses, the ship whose starboard side is clear has the right-of-way. The other vessel is required to maneuver as necessary to avoid a collision. In this case, the Mont Louis should have yielded the right-of-way to the Olau Britannia. Mont Louis (ship) Uranium hexafluoride Hazardous materials, shipping [kw]Radioactive Cargo Sinks in the North Sea (Aug. 25, 1984) [kw]Cargo Sinks in the North Sea, Radioactive (Aug. 25, 1984) [kw]North Sea, Radioactive Cargo Sinks in the (Aug. 25, 1984) [kw]Sea, Radioactive Cargo Sinks in the North (Aug. 25, 1984) Mont Louis (ship) Uranium hexafluoride Hazardous materials, shipping [g]Europe;Aug. 25, 1984: Radioactive Cargo Sinks in the North Sea[05510] [g]Belgium;Aug. 25, 1984: Radioactive Cargo Sinks in the North Sea[05510] [c]Disasters;Aug. 25, 1984: Radioactive Cargo Sinks in the North Sea[05510] [c]Environmental issues;Aug. 25, 1984: Radioactive Cargo Sinks in the North Sea[05510] Reinigert, Klaas Lengagne, Guy Longenecker, John R.

This collision occurred at night in heavy fog in the North Sea, just east of the eastern entrance to the English Channel, where ship traffic is among the heaviest in the world. The failure of the Mont Louis to maintain a proper lookout under these circumstances was thus surprising and negligent.

The Mont Louis carried a crew of twenty-three, whereas the Olau Britannia had a crew of eighty and carried more than nine hundred British, Dutch, and German passengers. Although some passengers suffered shock, no one was seriously hurt in the collision. Five members of the crew of the Mont Louis fell into the sea but were safely rescued.

Following the collision, the two ships remained locked together. Salvage tugs owned by the Belgian company Union de Remorquage et de Sauvetage were only two hours away. They sped to the scene and pulled the ships apart. Once the ships were separated, the Mont Louis immediately capsized and sank. It rested on its starboard side in about 45 feet of water with the port side visible above the sea. The crew of the Mont Louis went aboard the Olau Britannia, which sustained only minor damage. That vessel was able to continue to England under its own power.

The cargo of the Mont Louis included thirty containers holding 225 tons of uranium hexafluoride (UF 6 ). This material is mildly radioactive, and it reacts vigorously with seawater. The UF 6 containers were in the forward part of the ship, away from the impact of the collision toward the stern. The tightly sealed containers were designed to withstand the pressure of the sea at a depth of 200 meters (about 650 feet). Given that the water depth at the collision site was only 45 feet (less than 14 meters), the cargo was safe. Divers conducted surveys of the cargo at various times during the salvage process, and the first survey confirmed that the containers were intact. At no time was there any sign of radioactivity in the water.

Rules published by the International Maritime Organization, a part of the United Nations, state that ships of more than 1,600 gross registered tons are requested (but not required) to notify the authorities whose coasts they pass if they carry dangerous cargo. Because the Mont Louis was less than 1,600 tons, the ship had not notified authorities about the nature of its cargo. French authorities did not reveal the nature of the cargo until the environmental group Greenpeace, which opposes the transportation of radioactive material in this manner, publicly speculated about the presence of radioactive material aboard the Mont Louis.

The ship was carrying four hundred tons of fuel for its engines at the time of the collision, and some of the fuel leaked out and hampered salvage operations. Part of the fuel fouled a Belgian beach resort near Ostend. The oil slick, which was reported to be one thousand yards long and two hundred yards wide, was treated with chemical dispersants that broke it up into small droplets that would naturally decompose.

Smit Tak International, Smit Tak International a well-known salvage company, was hired to recover the containers of UF 6 and then raise the wreck itself. Klaas Reinigert, Smit Tak’s managing director, reported that the job was an easy one compared with most the company had done. The salvage crew cut a 10-foot by 17-foot hole in the exposed side of the ship and brought in a large floating crane to lift out the containers of UF 6 . Bad weather slowed the work down. On September 11, a storm broke the ship in half, but the last container was recovered on October 4, 1984, less than six weeks after the collision. The containers were placed on a barge and taken to the French port of Dunkirk. Efforts to raise the ship itself began on June 27, 1985, and were successfully completed on September 29, 1985. The cost of the salvage operation was $4.6 million, and the recovered UF 6 was worth 130 million French francs.


It is believed that the uranium on board the Mont Louis came originally from Canada, given that France has no supply of its own. Canadian uranium, in a form called yellowcake, was processed in France to make UF 6 . Transportation of UF 6 across the North Sea was a common event. In 1973, the Soviet Union signed contracts with France and other European countries for the enrichment of uranium. A plant near Riga enriched the uranium and returned it to its owner.

Naturally occurring uranium consists of two isotopes: U-238, which contains 92 protons and 146 neutrons in its nucleus, and U-235, which contains 92 protons and 143 neutrons. Less than 1 percent of mined uranium is U-235, and the rest is U-238. Only U-235 can undergo the splitting process known as fission that is the basis for the generation of electric power in a nuclear power plant. Fuel for a nuclear reactor must contain about 5 percent U-235 in order to maintain a chain reaction. Both isotopes give off radiation known as alpha particles. As alpha particles cannot penetrate human skin, these isotopes are not dangerous unless they are swallowed or inhaled.

Enrichment is the process of separating one isotope from the other. It is a difficult process, because the isotopes have the same chemical behavior. The most common enrichment process is called diffusion. First, uranium yellowcake is reacted with fluorine to make UF 6 . This is done because diffusion works only with gases, and UF 6 is the only known compound of uranium that turns into a gas at a reasonable temperature. If a molecule of UF 6 gas contains a U-235 atom, it will be lighter than if it contains a U-238 atom. The lighter molecules move faster, and the faster-moving molecules pass through a porous barrier more rapidly than the slower molecules. Thus the UF 6 gas outside a porous barrier is richer in U-235 than the gas inside. This process is repeated many times in the enrichment process.

Only a few enrichment plants exist in the Western world, partly because these plants consume enormous amounts of electricity. In fact, the diffusion plants operated by the U.S. Department of Energy are the nation’s single largest consumer of electricity. The United States performs two-thirds of the Western world’s enrichment at Oak Ridge National Laboratory Oak Ridge National Laboratory in Oak Ridge, Tennessee. France has a small plant at Pierrelatte near Lyons. The Soviet Union operated an enrichment plant near Riga, Latvia, that in 1973 offered to enrich uranium at a cost 10 percent below the U.S. price. After 1973, about twenty-five hundred containers of UF 6 were shipped to Riga from various European ports; even the Robert E. Ginna reactor, owned by Rochester Gas and Electric Corporation in Rochester, New York, once bought fuel that had been enriched at the Riga plant. Great Britain’s Central Electricity Generating Board sent about 10 percent of its UF 6 there. The Soviet Union’s purpose was to earn payments in dollars an important economic issue to the Soviets, because their own currency was virtually worthless in international trade.

French authorities belatedly revealed that the UF 6 in three of the containers on the Mont Louis was not made from freshly mined uranium. Instead, it was made from uranium recovered from used reactor fuel. When fuel is removed from a nuclear reactor, it still contains some U-235, and it contains most of the U-238 originally present. This uranium needs to be enriched again if it is to be reused. Unlike freshly mined uranium, recycled uranium contains fission products, the atoms that are produced when U-235 splits. Some of these fission products are highly radioactive. The recycling process separates the uranium from the fission products, but the separation cannot be 100 percent complete. If UF 6 is made from recycled uranium, it is contaminated by fission products; therefore, it is more radioactive than UF 6 made from freshly mined uranium. This additional radiation is of a more dangerous type, beta particles and gamma rays. These types of radiation have greater penetrating power than alpha particles, but the containers aboard the Mont Louis were probably lined with lead to prevent the escape of any radiation. As long as the containers were intact, there was no danger.

It was fortunate that the containers were stored in a forward cargo hold on the Mont Louis when the Olau Britannia struck near its stern. If the collision had involved the cargo hold where the UF 6 containers were stowed, the force of the collision could have ruptured some of them. A ruptured container would have released its UF 6 into the sea, and the radiation from the UF 6 would have escaped into the environment. The released radioactive material could have posed a hazard to anyone at the wreck site, including passengers and crew members of the two ships as well as salvage personnel recovering the damaged containers.

Because the crew of the Mont Louis had received no special training concerning the radioactive cargo, they were not prepared to take any special precautions after the collision. Indeed, they may not even have been aware of the nature of the cargo. If a container had ruptured, salvage personnel would have detected the presence of radioactivity in the water and taken precautions to protect themselves. As the UF 6 would have quickly mixed with seawater, it would not have been hazardous to anyone well away from the wreck.

Most observers considered the fact that no radioactivity was released as a result of the collision of the Mont Louis and the Olau Britannia to be largely a matter of good fortune. The potential for the release of the radioactive material transported aboard ships remained a matter of concern to many. Mont Louis (ship) Uranium hexafluoride Hazardous materials, shipping

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">“An Accident at Sea Raises Nuclear Alarms.” BusinessWeek, September 10, 1984, 58. Gives a brief account of the sinking and questions the wisdom of shipping radioactive material by sea. Discusses the planned shipment of enriched plutonium later in 1984.
  • citation-type="booksimple"

    xlink:type="simple">Angler, Natalle. “A Shipwreck Sends a Warning.” Time, September 10, 1984, 33. Brief article provides little information about the circumstances of the collision but includes a picture of the ship lying on its starboard side with its port side above the water and a good map of the collision region.
  • citation-type="booksimple"

    xlink:type="simple">Canine, Craig. “Tracking a Nuclear Near Miss.” Newsweek, September 10, 1984, 10. Brief article points out that the ship’s crew had recently been reduced in size, a factor that possibly contributed to the collision. Includes a picture of the wreck and a map of the area.
  • citation-type="booksimple"

    xlink:type="simple">Hooke, Norman. Modern Shipping Disasters, 1963-1987. London: Lloyd’s of London Press, 1989. Excellent general reference source provides a brief account of every merchant marine or naval ship lost in the period 1963-1987.
  • citation-type="booksimple"

    xlink:type="simple">Lamarsh, John R., and Anthony J. Baratta. Introduction to Nuclear Engineering. 3d ed. Upper Saddle River, N.J.: Prentice Hall, 2001. College-level textbook presents a clear, readable description of the uranium enrichment process. Includes excellent sketches of the enrichment apparatus.
  • citation-type="booksimple"

    xlink:type="simple">Mitchell, Jared. “Danger on the Channel Floor.” Maclean’s, September 10, 1984, 28. The Canadian weekly newsmagazine covered the story from a slightly different perspective compared with U.S. newsmagazines. Article refers to Japan’s plan to ship five hundred pounds of plutonium to France by sea.

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