The invention: The first nuclear reactor to produce substantial quantities of plutonium, making it practical to produce usable amounts of energy from a chain reaction.
The people behind the invention:
Enrico Fermi (1901-1954), an American physicist
Martin D. Whitaker (1902-1960), the first director of Oak Ridge
National Laboratory Eugene Paul Wigner (1902-1995), the director of research and development at Oak Ridge
The Technology to End a War
The construction of the nuclear reactor at Oak Ridge National Laboratory in 1943 was a vital part of the Manhattan Project, the effort by the United States during World War II (1939-1945) to develop an atomic bomb. The successful operation of that reactor was a major achievement not only for the project itself but also for the general development and application of nuclear technology. The first director of the Oak Ridge National Laboratory was Martin D. Whitaker; the director of research and development was Eugene Paul Wigner.
The nucleus of an atom is made up of protons and neutrons. “Fission” is the process by which the nucleus of certain elements is split in two by a neutron from some material that emits an occasional neutron naturally. When an atom splits, two things happen: A tremendous amount of thermal energy is released, and two or three neutrons, on the average, escape from the nucleus. If all the atoms in a kilogram of “uranium 235″ were to fission, they would produce as much heat energy as the burning of 3 million kilograms of coal. The neutrons that are released are important, because if at least one of them hits another atom and causes it to fission (and thus to release more energy and more neutrons), the process will continue. It will become a self-sustaining chain reaction that will produce a continuing supply of heat.
Inside a reactor, a nuclear chain reaction is controlled so that it proceeds relatively slowly. The most familiar use for the heat thus released is to boil water and make steam to turn the turbine generators that produce electricity to serve industrial, commercial, and residential needs. The fissioning process in a weapon, however, proceeds very rapidly, so that all the energy in the atoms is produced and released virtually at once. The first application of nuclear technology, which used a rapid chain reaction, was to produce the two atomic bombs that ended World War II.
Breeding Bomb Fuel
The work that began at Oak Ridge in 1943 was made possible by a major event that took place in 1942. At the University of Chicago, Enrico Fermi had demonstrated for the first time that it was possible to achieve a self-sustaining atomic chain reaction. More important, the reaction could be controlled: It could be started up, it could generate heat and sufficient neutrons to keep itself going, and it could be turned off. That first chain reaction was very slow, and it generated very little heat; but it demonstrated that controlled fission was possible.
Any heat-producing nuclear reaction is an energy conversion process that requires fuel. There is only one readily fissionable element that occurs naturally and can be used as fuel. It is a form of uranium called uranium 235. It makes up less than 1 percent of all naturally occurring uranium. The remainder is uranium 238, which does not fission readily. Even uranium 235, however, must be enriched before it can be used as fuel.
The process of enrichment increases the concentration of uranium 235 sufficiently for a chain reaction to occur. Enriched uranium is used to fuel the reactors used by electric utilities. Also, the much more plentiful uranium 238 can be converted into plutonium 239, a form of the human-made element plutonium, which does fission readily. That conversion process is the way fuel is produced for a nuclear weapon. Therefore, the major objective of the Oak Ridge effort was to develop a pilot operation for separating plutonium from the uranium in which it was produced. Large-scale plutonium production, which had never been attempted before, eventually would be done at the Hanford Engineer Works in Washington. First, however, plutonium had to be pro-
Part of the Oak Ridge National Laboratory, where plutonium was separated to create the first atomic bomb. (Martin Marietta)
duced successfully on a small scale at Oak Ridge.
The reactor was started up on November 4, 1943. By March 1, 1944, the Oak Ridge laboratory had produced several grams of plutonium. The material was sent to the Los Alamos laboratory in New Mexico for testing. By July, 1944, the reactor operated at four times its original power level. By the end of that year, however, plutonium production at Oak Ridge had ceased, and the reactor thereafter was used principally to produce radioisotopes for physical and biological research and for medical treatment. Ultimately, the Hanford Engineer Works’ reactors produced the plutonium for the bomb that was dropped on Nagasaki, Japan, on August 9, 1945.
The original objectives for which Oak Ridge had been built had been achieved, and subsequent activity at the facility was directed toward peacetime missions that included basic studies of the structure of matter.
Impact
The most immediate impact of the work done at Oak Ridge was its contribution to ending World War II. When the atomic bombs were dropped, the war ended, and the United States emerged intact. The immediate and long-range devastation to the people of Japan,
however, opened the public’s eyes to the almost unimaginable death and destruction that could be caused by a nuclear war. Fears of such a war remain to this day, especially as more and more nations develop the technology to build nuclear weapons.
On the other hand, great contributions to human civilization have resulted from the development of nuclear energy. Electric power generation, nuclear medicine, spacecraft power, and ship propulsion have all profited from the pioneering efforts at the Oak Ridge National Laboratory. Currently, the primary use of nuclear energy is to produce electric power. Handled properly, nuclear energy may help to solve the pollution problems caused by the burning of fossil fuels.
See also Breeder reactor; Compressed-air-accumulating power plant; Fuel cell; Geothermal power; Heat pump; Nuclear power plant; Solar thermal engine; Tidal power plant.
