CP-1 at 80: Preparing for the first controlled nuclear chain reaction

November 17, 2022, 3:08PMNuclear News
From left, the cover of the December 1962 issue of NN, featuring a model and a medal, both displayed at the 1962 ANS Winter Meeting; a photo of CP-1 during construction, as published in the November 1992 issue of NN; the opening page of a chronological account of CP-1, published in November 1992 to mark the 50th anniversary.

As we approach the 80th anniversary of controlled nuclear fission, Nuclear Newswire is prepared to deliver not one but three #ThrowbackThursday posts of CP-1 highlights unearthed from past issues of Nuclear News.

ANS was founded in 1954, nearly 12 years after the first controlled nuclear chain reaction was achieved on December 2, 1942, inside a pile of graphite and uranium assembled on a squash court at the University of Chicago’s Stagg Field. By 1962, ANS was prepared to “salute the 20th anniversary of the first chain reaction” at their Winter Meeting, displaying a model of Chicago Pile-1 and presenting a specially cast medal to Walter Zinn, a representative of Enrico Fermi’s scientific team. Over the years, ANS has continued to mark significant anniversaries of CP-1 at national meetings and in NN.

Today’s throwback: a look at activities in Chicago and around the country in 1942 prior to the successful experiment. “CP-1: The story of the first nuclear reactor,” published in the November 1992 issue of NN (p. 67) to mark the 50th anniversary and written by Nancy Zacha, then director of public communications for ANS (later to become editor of Nuclear News and then of Radwaste Solutions), sets the stage:

The year: 1942. As the year begins, World War II has been raging in Europe since September 1939 (with Germany now occupying Denmark, Norway, Belgium, The Netherlands, Luxembourg, France, several Balkan nations, Greece, and Crete), in the Soviet Union since June 1941, but in the United States, only a few weeks—since Pearl Harbor. During this year, Americans will first read William Faulkner's Go Down, Moses and John Steinbeck's The Moon Is Down. They will go to see Thornton Wilder's The Skin of Our Teeth on Broadway, and Bambi, Mrs. Miniver, and Holiday Inn at the movies. They will listen to Aaron Copland's "Rodeo" and Irving Berlin's "White Christmas". . . . Sugar and gasoline rationing will begin. . . . But it will be August 1945 before they know that a handful of scientists at a few locations around the country—Columbia University, the University of Chicago, the University of California at Berkeley, and Princeton University—are working on a project that will end the war, and change the lives of future generations forever.

January 1942: The action rises in a sickroom near the University of Chicago, where Arthur Holly Compton was recovering from the flu. Zacha writes:

Arthur Holly Compton, chairman of the Physics Department at the University of Chicago, was a man who hated to make decisions. He liked to mull things over and talk about them with his wife before he took any major steps. But this month, he had to make a decision: He had to decide the central location for a demonstration of the first sustained release of atomic energy-a self-sustaining nuclear chain reaction, with a view to producing plutonium. Projects under way at Columbia, Berkeley, Princeton, and Chicago had come under his authority in the wake of Pearl Harbor and the ensuing rush to mobilize a scattered research effort into a cohesive program. . . .

At a January 24 meeting at his home (he had the flu, and was bedridden), Compton suggested his own University of Chicago, where he knew he had the wholehearted support of the university administration. Also, scientists in the Midwest were available to staff the project, while university faculties and graduate schools on both coasts had been drained to support other war work (radar research, for example). Chicago was centrally located, making travel to other sites more convenient. And Chicago, being an inland city, was more protected from enemy attack than coastal sites.

These arguments did not convince the group gathered. But Compton was in charge, he was sick from the flu and sick and tired of arguing, and he made the decision: Chicago was to be the project's location. [Ernest O.] Lawrence thought the tempo of the University of Chicago was "too slow" to support the project. Compton countered that the chain reaction would take place before the end of the year. Lawrence bet a cigar that Compton was wrong.

Spring 1942: In February, Enrico Fermi, the scientific leader of the CP-1 team, moved to Chicago from New Jersey, where he had settled just three years earlier after leaving his native Italy with his family to accept the 1938 Nobel Prize in Physics (having carefully laid plans not to return to the fascist country with his Jewish wife and their children). Fermi was soon joined by others:

During the spring, physicists from around the country began to converge on the Met Lab. Glenn Seaborg arrived on April 19, his 30th birthday, to set up the plutonium separation laboratory. In addition to his work in plutonium chemistry, one of Seaborg's jobs for the next few months was recruiting, and he worried about asking people to give up their secure university positions to come to work at the Met Lab, where no one knew how long the work would last, nor how it would affect their careers. But although the duration was uncertain, most came to believe that the project was vitally important.

Others turned up that spring to join the project. In June, Edward Teller came to work in the theoretical group under Eugene Wigner. Also working with Wigner were two postdoctoral assistants, Gale Young and Alvin Weinberg.

Later in June, Robert Oppenheimer, a physics professor from Berkeley, came to Chicago.

Summer 1942: Work continued at the University of Chicago, where between April and October work crews built 18 successive piles in the Stagg Field stands, primarily to test the purity of the graphite and uranium oxide that had been delivered. But other work was underway around the country, including plutonium separations:

At both Chicago and elsewhere around the country, work ancillary to the first chain reaction proceeded apace. Seaborg's team began the tedious work of isolating plutonium from uranium nitrate hexahydrate (UNH) that had been bombarded with neutrons at the Washington University cyclotron. On August 20, Seaborg could report that the microchemists "isolated pure element 94 for the first time! . . . It is the first time that element 94 has been beheld by the eye of man."

Fall 1942: As the team approached their goal of demonstrating a nuclear chain reaction, the project began to receive more attention from the military:

In September, Henry L. Stimson, the Secretary of War, with the approval of President Roosevelt, appointed a new army officer to be in charge of the project: Colonel (soon promoted to Brigadier General) Leslie R. Groves. As the engineer in charge of all military construction, Groves had just completed the building of the Pentagon. Now, however, he was looking forward to an overseas assignment. He was not pleased to be assigned to a project he characterized as "founded on possibilities rather than probabilities."

His first meeting with the director of the Office of Scientific Research and Development, Vannevar Bush, was not auspicious. Bush was particularly struck by Groves' brusque manner and lack of tact. "I'm afraid he may have trouble with the scientists," Bush noted later. This proved to be the understatement of the project.

By November of that year, the University of Chicago team was faced with a siting challenge that would force a change of plans for CP-1:

The final pile—the self-sustaining one—was to be built in a special facility located on a site in the Argonne Woods west of Chicago. But a labor strike against the constructor hopelessly delayed completion of the building, originally scheduled to be finished in mid-October. Fermi paused to recalculate the risks of controlling the reaction. In early November, he approached Compton and proposed that the team stay at the Stagg Field stands. But the chain-reacting pile presented a situation far different from the exponential piles that preceded it. Compton was again faced with a decision of staggering dimensions.

"We did not see how a true nuclear explosion, such as that of an atomic bomb, could possibly occur," Compton wrote later. "But the amount of potentially radioactive material present in the pile would be enormous and anything that would cause excessive ionizing radiation in such a location would be intolerable." Fermi calculated the control capabilities once more and expressed his confidence that the reaction could be controlled. Reassured, Compton agreed. He did not, however, inform the president of the university. "The only answer he could have given would have been—no. And this answer would have been wrong. So I assumed responsibility myself." Compton added that to have informed the university president would have meant asking a lawyer to judge a matter of nuclear physics, something he felt to be inappropriate.

When Gen. Groves found out about this decision somewhat later, he was initially quite upset, envisioning among other things what might happen to his Army career if the south side of Chicago were to suddenly disappear. Ultimately, he decided that it would be unwise to interfere.

Look for more: We’ll leave it there for now and return with more about the successful build of CP-1 later, but Zacha’s account contains many more details about its preparations, free for ANS members to read in the NN archive.

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