World’s First Nuclear Reactor Is Activated

The reactor at Oak Ridge National Laboratory produced the first substantial quantities of plutonium, making the production of usable amounts of energy from a chain reaction practical. The reactor played a major part in the development of the first nuclear bomb.

Summary of Event

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 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 and the director of research and development was Eugene P. Wigner. [kw]World’s First Nuclear Reactor Is Activated (Nov. 4, 1943)[Worlds First Nuclear Reactor Is Activated]
[kw]Nuclear Reactor Is Activated, World’s First (Nov. 4, 1943)
[kw]Reactor Is Activated, World’s First Nuclear (Nov. 4, 1943)
Nuclear energy;reactors
Nuclear weapons;invention
Oak Ridge National Laboratory
Manhattan Project
Nuclear energy;reactors
Nuclear weapons;invention
Oak Ridge National Laboratory
Manhattan Project
[g]North America;Nov. 4, 1943: World’s First Nuclear Reactor Is Activated[00980]
[g]United States;Nov. 4, 1943: World’s First Nuclear Reactor Is Activated[00980]
[c]Engineering;Nov. 4, 1943: World’s First Nuclear Reactor Is Activated[00980]
[c]Science and technology;Nov. 4, 1943: World’s First Nuclear Reactor Is Activated[00980]
[c]Energy;Nov. 4, 1943: World’s First Nuclear Reactor Is Activated[00980]
Fermi, Enrico
Whitaker, Martin D.
Wigner, Eugene P.

The nucleus of an atom is made up of protons and neutrons. A nuclear reaction for any purpose involves the fissioning, or splitting, of the nucleus of a fissionable atom by hitting it with a neutron from a material that emits an occasional neutron naturally. Nuclear fission 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 (U-235) were to fission, they would produce as much heat energy as the burning of 3,000,000 kilograms of coal.

The benefit of the energy released during fission is obvious, but the extra neutrons also are important, because if at least one of them hits another atom and causes it to fission (and thus 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. On the other hand, the fissioning process in a weapon proceeds very rapidly so that all of the energy in the atoms is produced and released virtually at once. Therefore, the first application of nuclear technology was to produce the two atomic bombs that ended World War II.

Oak Ridge National Laboratory around 1944. The first nuclear reactor was housed in the white building at right center.

(Courtesy, Martin Marietta)

The work that began at Oak Ridge in 1943, however, had to be preceded 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 and proved the principle that controlled fission was possible.

Slow or fast, however, a heat-producing nuclear reaction is an energy conversion process, and it 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 U-235. It is, however, a rare form. Only 0.7 percent, one part in 140, of all naturally occurring uranium Uranium is U-235. The remainder is U-238, which does not fission readily. Therefore, the concentration of the “active ingredient,” U-235, is not high enough to achieve a “critical mass” of a reasonable size. The critical mass is the amount of fissionable material needed for a chain reaction. One way around this problem is the process of enrichment, which increases the concentration of U-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 U-238 can be converted into Pu-239, a form of the synthetic element plutonium Plutonium , which does fission readily. That conversion process is the way fuel is produced for a nuclear weapon, and was, thus, the major objective of the Oak Ridge effort: 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, it had to be proved on a small scale at Oak Ridge.

Four rural eastern Tennessee communities—Wheat, Elza, Robertsville, and Scarboro—lay not far from Knoxville in the valley beside the Clinch River where the U.S. government acquired twenty-four thousand hectares needed for the Oak Ridge facility. On its first visit to the area, the site selection committee was pleased with what it saw and made the following report:

The topography is such that a number of operations could find reasonably flat areas divided by protective hills. The driving distance to Knoxville is less than twenty miles, and service from two important railroads is immediately available. . . . Water from the Clinch River is regulated . . . and because of the nearby Norris Dam is relatively free of silt. A relatively small part of the land is under cultivation, indicating that a small number of families would have to be moved.

One thousand families were paid a total of $2.6 million for their property by the government, which relocated the former residents and agreed to care for the sixty-five cemeteries that also were purchased. Ground was broken for the construction of the Oak Ridge reactor on February 1, 1943, only two months after Fermi’s success in Chicago. In fact, the basic data for the design of the Oak Ridge facility came from the original Chicago reactor. Oak Ridge was the world’s first operating nuclear reactor to produce substantial amounts of heat, and it was built in only nine months. The reactor was started up on November 4 under Fermi’s supervision and was flawless.

The Oak Ridge laboratory (originally called Clinton Laboratories) was constructed by the Du Pont Corporation Du Pont Corporation[Dupont Corporation] and operated by the Metallurgical Laboratory of the University of Chicago. The facility produced several grams of plutonium by March 1, 1944. The material was sent to the Los Alamos laboratory in New Mexico for testing. By July 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’ Hanford Engineer Works reactors in Washington State produced the plutonium for the bomb that was dropped on Nagasaki on August 9, 1945.

At first, Oak Ridge was essentially a “company town” built and run by the federal government. A planned community for laboratory employees and their families, it was complete with grocery stores, schools, and all the standard features of any other separate community. It was, however, completely fenced in and secured by armed guards. In two and a half years, Oak Ridge became the fifth largest city in Tennessee, with a population that peaked at seventy-five thousand. When the war was over, however, the population fell to thirty-six thousand.

In July, 1945, Monsanto Chemical Company Monsanto Chemical Company took over operating responsibility for Oak Ridge. The production of radioisotopes was expanded, and work began on designing two additional reactors. 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.


When the bombs were dropped, the war stopped. Reduced to simplest terms, the most immediate impact of the work done at Oak Ridge was its contribution to ending World War II, with the United States emerging intact to remain the principal preserver of freedom in the world. History since 1945 undeniably would have been much different if the United States’ victory in the Pacific had not been decisive.

Nuclear technology, like any other technology, is neutral and can be developed for and applied to a variety of purposes. Interestingly enough, the great advances in nuclear technology since 1945 have not been for military uses. Delivery systems have changed dramatically, but the real advances in and new applications of nuclear technology have been in nonmilitary areas: terrestrial electric power generation, nuclear medicine, space power, and ship propulsion (even though it is principally for naval vessels). All those areas have profited from the pioneering efforts at the Oak Ridge National Laboratory. Nuclear energy;reactors
Nuclear weapons;invention
Oak Ridge National Laboratory
Manhattan Project

Further Reading

  • Bernardini, Carlo, and Luisa Bonolis, eds. Enrico Fermi: His Work and Legacy. New York: Springer, 2004. A laudatory history of Fermi, his work, and his place in the development of nuclear physics. Includes the chapters “The Birth of Nuclear Energy: Fermi’s Pile” and “From the Chicago Pile 1 to the Next-Generation Reactors.”
  • Faulkner, Peter, ed. The Silent Bomb: A Guide to the Nuclear Energy Controversy. New York: Vintage Books, 1977. Sponsored by Friends of the Earth, this book deals with the controversies of “safe” radiation levels, potential disasters at nuclear plants, and the economics of nuclear power.
  • Glasstone, Samuel. Sourcebook on Atomic Energy. 3d ed. Huntington, N.Y.: Krieger, 1979. A balanced presentation of all aspects of atomic energy, it requires only a rudimentary knowledge of science or mathematics to understand its narrative. An excellent source book for the laboratory or library.
  • Hales, Peter B. Atomic Spaces: Living on the Manhattan Project. Urbana: University of Illinois Press, 1997. A unique cultural history of the communities created, and destroyed, to make way for the Manhattan Project. A relevant story for all communities displaced by the government’s nuclear programs, including the towns cleared to build Oak Ridge. A recommended study at the intersection of technology and culture. Bibliographical references, index.
  • Hewlett, R. G., and O. E. Anderson, Jr. The New World 1939/1946. Vol. 1 of A History of the United States Atomic Energy Commission. University Park: Pennsylvania State University Press, 1962. The first in a series, this volume discusses the discovery of atomic fission, the race to produce the first bomb, and the problems of control and of harnessing the energy.
  • Inglis, David Rittenhouse. Nuclear Energy: Its Physics and Its Social Challenge. Reading, Mass.: Addison-Wesley, 1973. A basic primer for readers interested in nuclear energy and its history, applications, and control. Presents the social challenges inherent in this energy source.
  • Olwell, Russell B. At Work in the Atomic City: A Labor and Social History of Oak Ridge, Tennessee. Knoxville: University of Tennessee Press, 2004. A brief but comprehensive history of the people and community of Oak Ridge, site of the nuclear laboratory and reactor. Discusses the employees that make up the “company town,” the community’s transformation after World War II, and postwar health and safety concerns.
  • Seaborg, Glenn T. Nuclear Milestones: A Collection of Speeches. San Francisco: W. H. Freeman, 1972. A series of speeches and reminiscences by a nuclear physicist who was part of the growth of nuclear energy and knew the major personalities of the new discipline. Lavishly illustrated with photographs.
  • Wilson, Jane, ed. All in Our Time: The Reminiscences of Twelve Nuclear Pioneers. Chicago: Bulletin of the Atomic Scientist, 1975. The twelve pioneers depicted assisted in the long labor and birth of nuclear energy, nursing it through wartime, and watching it grow to maturity in a world of peace. Easy and readable, it provides glimpses, occasionally humorous, into the thoughts and feelings of modern-day pioneers.

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