Chicago Pile-1

Chicago Pile-1 was the first human-made nuclear reactor to achieve a controlled, self-sustaining chain reaction. It reached criticality on December 2, 1942, beneath the stands of Stagg Field at the University of Chicago.

Nuclear fission: The splitting of an atomic nucleus into lighter nuclei, releasing energy and usually additional neutrons. Fission in uranium supplied the neutrons and heat that sustained the pile’s reaction.
Manhattan Project: The United States–led wartime program that developed the first nuclear weapons during World War II. Chicago Pile-1 was built within the project’s effort to demonstrate a controlled chain reaction.
Walter Zinn: A Canadian-American physicist who worked on reactor development and led the construction of Chicago Pile-1. Zinn oversaw the pile’s assembly and helped operate the criticality experiment.
X-10 Graphite Reactor: A graphite-moderated reactor built at Oak Ridge, Tennessee, to produce and study plutonium. It extended the pile’s demonstration into a reactor designed to irradiate uranium at greater scale.
Nuclear chain reaction: A sequence in which neutrons from one nuclear reaction trigger further nuclear reactions. The pile became self-sustaining when each fission produced, on average, enough neutrons to cause another.
Metallurgical Laboratory: A University of Chicago research laboratory established during the Manhattan Project to study plutonium production and reactor design. The laboratory’s scientists and engineers designed and built the pile.
Leó Szilárd: A Hungarian-American physicist who conceived the nuclear chain reaction and advocated research into its military implications. Szilárd helped develop the chain-reaction research program that led to the pile.
Hanford Site: A United States nuclear production complex in Washington state built during the Manhattan Project. The pile’s success helped justify construction of large reactors at Hanford for plutonium production.
Graphite moderator: Graphite used to slow fast neutrons, increasing their likelihood of causing fission in certain nuclear fuels. Its graphite blocks slowed neutrons so uranium-235 fissions could sustain the reaction.
University of Chicago: A private research university founded in Chicago in 1890. The pile was assembled beneath the west stands of the university’s Stagg Field.

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