Chicago Pile-1

As engineer Hank Kosmata explains, the Manhattan Project scientists used Enrico Fermi’s “pile” as the basis for the world’s first full-scale nuclear reactor at Hanford, Washington.

Narrator: In 1939, the scientific community was coming to terms with the discovery of nuclear fission, or the splitting of an atom. Scientists believed that the process of splitting the nucleus of an atom would produce a self-sustaining series of reactions, or a chain reaction. But could such a chain reaction be produced and controlled? Enrico Fermi set out to determine just that.

Hank Kosmata: Fermi’s idea is to build a large pile, as he called it, of graphite bars, interspersed with uranium. And he theorizes, along with his other fellow scientists, that if he gets it at the right geometry, then the neutrons that are generated will be confined into the uranium in the pile, and at the appropriate geometry he’ll get a chain reaction. And it’s also very critical that there are no other impurities in the graphite or the uranium, because they can absorb neutrons.

Narrator: To test his theory, Fermi built his test reactor, or pile, as he called it, under the squash courts at the University of Chicago. On December 2, 1942, he was able to begin the reaction and continue it until it was self-sustaining, or went critical. Even more important, Fermi could control the reaction and stop it when he wanted to.

Hank Kosmata: So that, basically, was the background for the reactor at Hanford. A pile of graphite, with the uranium in it. The difference is, this one is now introducing cooling materials to take away the incredible amount of heat.

Narrator: Fermi’s work in Chicago proved that humans could control a nuclear chain reaction. But taking the first crude nuclear reactor in Chicago and building one of the scale and complexity required at Hanford would require incredible technical expertise and ingenuity.

Peter Vandervoort describes the West Stands of Stagg Field, where Manhattan Project scientists and workers constructed the world’s first artificial nuclear reactor, Chicago Pile-1.

Narrator: An Italian immigrant, Enrico Fermi was known the “Pope of Physics” because he was “infallible” when it came to problems involving physics. In 1942, Fermi was in charge of designing a physics experiment that would create a self-sustaining nuclear chain reaction. The squash court underneath the West Stands of Stagg Field seemed to be an ideal place to build what would become known as Chicago Pile-1. Peter Vandervoort remembers.

Peter Vandervoort: The West Stands was located along Ellis Avenue between 57^th and 56^th Streets. It was part of Stagg Field, which was the original athletic field on the campus of the university.

When I was a student, the West Stands loomed over Ellis Avenue, an industrial quality structure suitable for scientific research of the kind that was required for the construction of CP-1. In any case, it was appropriated and secured as part of the Metallurgical Lab, and was the venue for the first controlled nuclear chain reaction in December of 1942.

Crawford Greenewalt, Herbert Anderson, and Arthur Holly Compton recall when Chicago Pile-1 went critical – the moment that ushered in the nuclear age.

Narrator: Forty-nine people gathered on the small balcony above the squash court on the afternoon of December 2, 1942. In the words of Richard Rhodes, the experimental reactor below looked like “an ominous black beehive in a bright box.” Here are three eyewitness accounts to the event that marked the beginning of the Atomic Age. You will hear from Crawford Greenewalt, Herbert Anderson, and Arthur Holly Compton.

Crawford Greenewalt: The whole atmosphere there was one of calmly observing an experiment being made. To be sure, there was a suicide squad that you could see on the other end of the other platform ready to pour [cadmium nitrate] in if it did not work. But it became obvious very quickly that it was going to be controlled.

Herbert Anderson: He [Fermi] made an initial test of the activity, and then called for withdrawal of the control rod and made another measurement of the radioactivity generated. Then, with a slide rule, he calculated what would be the effect if he took the rod out somewhat more. [He] announced this. He said, “Now you look at this and it will rise this high.” They pulled out the rod and it went that high and the counters clicked a little more. [He] kept this up a number of times, each time being right about it.

Arthur Holly Compton: We entered the balcony at one end of the room. On the balcony, a dozen scientists were watching the instruments and handling the controls. Across the room was a large cubical pile of graphite and uranium blocks, in which we hoped the atomic chain reaction would develop. Inserted into openings in this pile of blocks were control and safety rods.

After a few preliminary tests, Fermi gave the order to withdraw the control rod another foot. We knew that that was going to be the real test. The Geiger counters registering the neutrons from the reactor began to click faster and faster, until their sound became a rattle. The reaction grew until there might be danger from the radiation up on the platform where we were standing.

“Throw in the safety rods,” came Fermi’s order. And you could see the pointer move right back to zero. The rattle of the counters fell to a slow series of clicks. For the first time, atomic power had been released. It had been controlled and stopped.

One of the things that I shall not forget is the expressions on the faces of some of the men. There was Fermi’s face—one saw in him no sign of elation. The experiment had worked just as he had expected, and that was that. Cool and collected—Fermi’s face was that of a competent man of action busily engaged on the one important job.

Eyewitnesses Leona Marshall Libby and Crawford Greenewalt and Leo Szilard biographer William Lanouette describe how the scientists reacted to the Chicago Pile-1’s success.

Narrator: What was the mood among the scientists on this historic occasion? Surprisingly subdued. Even a celebratory bottle of wine did not lift their spirits as they contemplated how the world would never be the same. Manhattan Project veterans Leona Marshall Libby and Crawford Greenewalt reflect on the moments after the Chicago Pile-1 went critical for the first time.

Leona Marshall Libby: Somewhat later, after the control rods were all put to bed and the charts were pulled out and clipped up and so on, Eugene Wigner showed up with a famous little flask of Chianti. He poured it into a paper cup. He went and drank it very quietly. There was no toast, nothing, no remarks. Nothing very dramatic, really: The most effective kind of drama probably at that point.

Crawford Greenewalt: I remember very well Wigner reaching under a desk and pulling out a bottle of Chianti in a brown paper bag, and handing it to Fermi with a bow. Well, here again, no great excitement, no cheers, just satisfaction that the experiment had worked. I think that was really the feeling that I had in my mind—“Thank God that one’s over.”

Narrator: Leo Szilard biographer William Lanouette describes Szilard’s reaction.

William Lanouette: Szilard and Fermi found themselves standing together on the balcony that overlooked the squash court. And at that point Szilard turned and shook Fermi’s hand and congratulated him, and then announced, “This day will go down as a black day in the history of mankind.”

Peter Vandervoort recalls Nobel Prize winner Subrahmanyan Chandrasekhar’s conversation with artist Henry Moore about his sculpture “Nuclear Energy,” which today marks the site of Chicago Pile-1.

Narrator: Today, the site of the Chicago Pile-1 is a large bronze sculpture by Henry Moore called “Nuclear Energy.” Peter Vandervoort recalls a conversation that his advisor, Nobel Prize-winning physicist Subrahmanyan Chandrasekhar, had with sculptor Henry Moore.

Peter Vandervoort: Chicago Pile-1 was constructed on the main floor of the West Stands. The building was eventually taken down. It has been replaced by a number of other structures, and in particular, it is the site of the sculpture “Nuclear Energy” by Henry Moore.

Subrahmanyan Chandrasekhar was my Ph.D. thesis supervisor. Professor Chandrasekhar knew Henry Moore, who did the “Nuclear Energy” sculpture essentially on the site of Chicago Pile-1. Chandra once commented that he had been discussing the interpretation of the sculpture with Henry Moore, and Chandra pointed out that many people saw the sculpture as a representation of a mushroom cloud or a skull. Henry Moore’s observation was that that interpretation was rather banal.

The sculpture, “Nuclear Energy,” is a tourist attraction. It is not uncommon to see buses pause there and visitors out taking pictures of the sculpture.

Narrator: The “Nuclear Energy” sculpture evokes a lot of different reactions. What is yours?

This short video, courtesy of Argonne National Laboratory, uses LEGO to recreate the Chicago Pile-1 experiment.

Narrator: In 1942, underneath the University of Chicago’s football stadium, a group of scientists led by Enrico Fermi built the world’s first nuclear reactor. The reactor was built out of graphite blocks, some of which contained small disks of uranium. Fermi knew if they arranged the blocks correctly, it would produce a self-sustaining nuclear reaction. A sphere would’ve been the best shape for the reactor, but Fermi’s team couldn’t build a perfect sphere out of rectangular blocks, and they weren’t sure exactly how big the reactor needed to be.

There were no instructions to follow, so they conducted a series of experiments to estimate the correct size for the reactor. First, they built a rectangular pile. Then they ran an experiment. One scientist slowly pulled control rods out of the pile, which allowed the nuclear reaction to proceed. Another monitored the reaction on instruments nicknamed after Winnie the Pooh characters. Other scientists stood by with containers of cadmium nitride in case of an emergency.

The measurements from this experiment helped Fermi conclude that the final reactor needed to be a rough sphere with a diameter of about 25 feet. They took apart the experimental pile and began construction on the reactor, which they called Chicago Pile-1.

As the pile grew, the team repeated the same experiment again and again. The data from these experiments allowed Fermi to conclude that the reactor didn’t need to be built all the way to the height he initially planned. After the 57^th layer of the pile was in place, Fermi called construction to a halt.

On December 2, 1942, Fermi assembled the whole team to watch the experiment. That morning, they pulled out the control rods as usual. The Geiger counter beeped faster and faster, indicating their goal was close. Fermi knew that with one small adjustment they could run the experiment again and achieve their long-anticipated goal.

So, he called for a lunch break. After lunch, the experiment resumed.

[Tense music swells]

Criticality had been achieved. The team toasted their accomplishment with Chianti drunk from small paper cups.

Thanks to Argonne National Laboratory for granting us permission to use this video.