04 February 2009

Atomic-powered ship

The invention: The world’s first atomic-powered merchant ship demonstrated a peaceful use of atomic power. The people behind the invention: Otto Hahn (1879-1968), a German chemist Enrico Fermi (1901-1954), an Italian American physicist Dwight D. Eisenhower (1890-1969), president of the United States, 1953-1961 Splitting the Atom In 1938, Otto Hahn, working at the Kaiser Wilhelm Institute for Chemistry, discovered that bombarding uranium atoms with neutrons causes them to split into two smaller, lighter atoms. A large amount of energy is released during this process, which is called “fission.” When one kilogram of uranium is fissioned, it releases the same amount of energy as does the burning of 3,000 metric tons of coal. The fission process also releases new neutrons. Enrico Fermi suggested that these new neutrons could be used to split more uranium atoms and produce a chain reaction. Fermi and his assistants produced the first human-made chain reaction at the University of Chicago on December 2, 1942. Although the first use of this new energy source was the atomic bombs that were used to defeat Japan in World War II, it was later realized that a carefully controlled chain reaction could produce useful energy. The submarine Nautilus, launched in 1954, used the energy released from fission to make steam to drive its turbines. U.S. President Dwight David Eisenhower proposed his “Atoms for Peace” program in December, 1953. On April 25, 1955, President Eisenhower announced that the “Atoms for Peace” program would be expanded to include the design and construction of an atomicpowered merchant ship, and he signed the legislation authorizing the construction of the ship in 1956.Savannah’s Design and Construction A contract to design an atomic-powered merchant ship was awarded to George G. Sharp, Inc., on April 4, 1957. The ship was to carry approximately one hundred passengers (later reduced to sixty to reduce the ship’s cost) and 10,886 metric tons of cargo while making a speed of 21 knots, about 39 kilometers per hour. The ship was to be 181 meters long and 23.7 meters wide. The reactor was to provide steam for a 20,000-horsepower turbine that would drive the ship’s propeller. Most of the ship’s machinery was similar to that of existing ships; the major difference was that steam came from a reactor instead of a coal- or oil-burning boiler. New York Shipbuilding Corporation of Camden, New Jersey, won the contract to build the ship on November 16, 1957. States Marine Lines was selected in July, 1958, to operate the ship. It was christened Savannah and launched on July 21, 1959. The name Savannah was chosen to honor the first ship to use steam power while crossing an ocean. This earlier Savannah was launched in New York City in 1818. Ships are normally launched long before their construction is complete, and the new Savannah was no exception. It was finally turned over to States Marine Lines on May 1, 1962. After extensive testing by its operators and delays caused by labor union disputes, it began its maiden voyage from Yorktown, Virginia, to Savannah, Georgia, on August 20, 1962. The original budget for design and construction was $35 million, but by this time, the actual cost was about $80 million. Savannah‘s nuclear reactor was fueled with about 7,000 kilograms (15,400 pounds) of uranium. Uranium consists of two forms, or “isotopes.” These are uranium 235, which can fission, and uranium 238, which cannot. Naturally occurring uranium is less than 1 percent uranium 235, but the uranium in Savannah‘s reactor had been enriched to contain nearly 5 percent of this isotope. Thus, there was less than 362 kilograms of usable uranium in the reactor. The ship was able to travel about 800,000 kilometers on this initial fuel load. Three and a half million kilograms of water per hour flowed through the reactor under a pressure of 5,413 kilograms per square centimeter. It entered the reactor at 298.8 degrees Celsius and left at 317.7 degrees Celsius. Water leaving the reactor passed through a heat exchanger called a “steam generator.” In the steam generator, reactor water flowed through many small tubes. Heat passed through the walls of these tubes and boiled water outside them. About 113,000 kilograms of steam per hour were produced in this way at a pressure of 1,434 kilograms per square centimeter and a temperature of 240.5 degrees Celsius. Labor union disputes dogged Savannah‘s early operations, and it did not start its first trans-Atlantic crossing until June 8, 1964. Savannah was never a money maker. Even in the 1960’s, the trend was toward much bigger ships. It was announced that the ship would be retired in August, 1967, but that did not happen. It was finally put out of service in 1971. Later, Savannah was placed on permanent display at Charleston, South Carolina. Consequences Following the United States’ lead, Germany and Japan built atomic-powered merchant ships. The Soviet Union is believed to have built several atomic-powered icebreakers. Germany’s Otto Hahn, named for the scientist who first split the atom, began service in 1968, and Japan’s Mutsuai was under construction as Savannah retired. Numerous studies conducted in the early 1970’s claimed to prove that large atomic-powered merchant ships were more profitable than oil-fired ships of the same size. Several conferences devoted to this subject were held, but no new ships were built. Although the U.S. Navy has continued to use reactors to power submarines, aircraft carriers, and cruisers, atomic power has not been widely used for merchant-ship propulsion. Labor union problems such as those that haunted Savannah, high insurance costs, and high construction costs are probably the reasons. Public opinion, after the reactor accidents at Three Mile Island (in 1979) and Chernobyl (in 1986) is also a factor.


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