Personal and Professional Reflections
Chain Reactions

At a recent mixed-age holiday party, a few of us who were former ORNL colleagues were reflecting on important past scientific events and conjecturing the outcomes of future possibilities. In the nuclear field, we particularly discussed the anticipated widespread use of small modular reactors (SMRs) as fail-safe nuclear power stations. During the conversation I remarked, “The last ORNL newsletter had a reprint of an article about Enrico Fermi’s death 60 years ago.” While my colleagues nodded “yes,” the expression on one teenager’s face could be translated to “Who?”

“You don’t know who Enrico Fermi was?” I asked her. She responded with a negative shake of her head and a slight shrug of her shoulders.

I told her that he was the World War II physicist who led the team that achieved the first self-sustaining controlled nuclear chain reaction in the world. That elicited an audible “Oh” from her, but hearing other subjects being bounced around in the room, I realized I did not have an audience. So I dropped the subject and did not inform the group that the article said Fermi last visited Oak Ridge National Laboratory in 1948, which was the same year I hired in.

That revelation, of course, would have been meaningful only to me, and I must admit that at the time I probably was not even aware of his visit—or possibly even of his personal involvement in the fission chain discovery. I, too, was once young, and when I hired in, all operations in Oak Ridge were still highly secret. Moreover, my circle of friends was very small. In fact, during my first six weeks of employment, while I was being vetted by the FBI, I was protected from learning anything about anything by being kept in a secluded room and escorted out periodically as was necessary.

But while Fermi’s name may not have been in my personal lexicon, by 1948 I was certainly aware of the debate that had already begun as to whether the success of the nuclear chain reaction was the greatest or the worst thing that mankind had ever done. That debate was anticipated by Fermi and the other 49 scientists who witnessed that momentous event on December 2, 1942. One of them, University of Chicago physicist Samuel K. Allison, later wrote, “All of us…knew that with the advent of the chain reaction, the world would never be the same again.” All of them also knew that our adversaries in World War II were working on a similar project.

In the early 1950s, I was helping an ORNL engineer write a reactor safeguards report when the subject of the first sustained nuclear reaction was mentioned. The engineer, whose name was Charles E. Clifford, casually remarked that he had had some connection to the project. It was then that I began to get a broader perspective of just what had happened and where it had happened.

As a simple Google search reveals in a number of publications, the experimental configuration in which the event occurred was assembled in the center of a 30-by 60-foot room under the West Stands of Stagg Field at the University of Chicago. Called Chicago Pile Number One (or CP-1), it “consisted of a massive lattice pile of 400 tons of graphite, six tons of uranium metal, and 50 tons of uranium oxide fuel.” The pile, which had wood supports, began as a square at the bottom and then was shaped upward into a sphere with a flat top.

The goal of the experiment was to initiate a chain reaction in which the nuclei of uranium atoms were hit and split by neutrons ejected from previously split uranium nuclei. The target nuclei were those of the isotope uranium 235 (235U), which comprises only 0.7% of natural uranium but is highly fissionable when hit by neutrons having the right energy. The purpose of the graphite was to slow the energies of the ejected neutrons to the optimum energy for effecting the split (i.e., fission). The entire process was to be controlled by manually inserting and withdrawing cadmium “control” rods distributed throughout the pile, it being known that cadmium had a high probability of absorbing neutrons and therefore could slow or stop the chain reaction.

In a University of Chicago history of the project, it was reported that once Fermi gave the signal to begin the process, it took only 28 minutes for the sustained reaction to occur—that is, for “criticality” to be reached. “If harnessed,” the report said, “the energy produced was only enough to light a bulb, but man had unleashed and controlled the energy of the atom.” When those witnessing the event realized that success had been achieved, they began quiet applause as a tribute to Enrico Fermi, who, more than any other person, was responsible for that success. No doubt they were also realizing that the experiment had placed them another step closer to developing an atomic bomb for which the percentage content of the 235U isotope in the uranium fuel would be greatly increased (enriched) to unleash unfathomable power.

Additional experiments were performed at CP-1, some at a maximum power of 200 watts, but they were terminated after three months and plans were made to relocate the pile in a wooded region called Red Gate. There operations could be conducted in a more secluded area and a shield could be added to protect the operators. The new pile would be called CP-2.

It was when the CP-1 was being dismantled that my colleague Clifford’s connection with the project began. He had graduated with a chemical engineering degree from the University of Oklahoma in 1942 and had immediately been hired by DuPont, a company with operational responsibilities within the country’s large war-time Manhattan project, of which CP-1 was a critical component. DuPont had sent Clifford and other new hires to Chicago as engineering trainees whose first task was to dismantle and rebuild the pile. I was shocked to hear him say that they performed the task “with our bare hands,” apparently with no concern for the effects of the radioactive fission products left in the pile. I have since read that the scientific team was confident that the radioactivity would be sufficiently low to cause no harm, and apparently they were correct.

The conversion from CP-1 to CP-2 took 21 days and constituted Clifford’s first introduction to the Manhattan Project. I have no idea how much he was told about the secret experiments. But he had to have known that the success of CP-1 had almost certainly assured the success of a third pile already under construction at Clinton Engineer Works (or Clinton Laboratories) in Oak Ridge, Tennessee. Tagged as the X-10 Pile, it was to be the world’s first nuclear reactor. It was also to be a pilot production plant for larger scale reactors under construction at Hanford, Washington, that were designed to produce a second potential bomb fuel—the fissile isotope plutonium 239 (239Pu).

The X-10 Pile, later known as the ORNL Graphite Reactor, was a much larger and more sophisticated version of the Chicago piles. It consisted of a 24-foot-square of tightly fitting graphite blocks weighing several hundred tons, and its natural uranium fuel was in the form of slugs that were manually inserted into horizontal tubes embedded in the graphite. Because of its size and intended long-term use, an internal coolant system was essential and was provided by air drawn through the reactor. And like the Chicago piles, it had cadmium control rods. Finally, to protect the operators, the entire configuration was surrounded by a 7-foot-thick concrete wall, later determined to be overdesigned.

On November 4, 1943, Clifford and his fellow DuPont engineers, all of whom were in training for later operation of the Hanford reactors, were present when the X-10 Pile reached criticality for the first time, only 11 months after the first chain reaction in CP-1. In an ORNL paper entitled “A Visit from St. Nucleus,” scientist Henry Newson described how a skeleton crew that included the DuPont engineers was continuing the long and meticulous process of loading the fuel during the previous night in preparation for the major event the next day. Suddenly and unexpectedly they realized that the process had proceeded so well they were in danger of being the only witnesses when the pile reached criticality. They immediately ceased adding fuel and notified Fermi and the expected scientific and management contingent. When they appeared, Fermi was apprised of the status of the loading and he soon ordered the final additions of uranium.

The reactor went critical at 5:00 AM, and the X-10 Pile fulfilled its mission as the world’s first nuclear reactor. It was a huge scientific accomplishment in the Manhattan Project and the second one largely attributed to the efforts of Enrico Fermi, the emigrant scientist known in his secret circle of colleagues as the “Italian navigator.”

The X-10 Pile also subsequently fulfilled its second mission of being the world’s first pilot plant for the production of 239Pu, which was created within the uranium fuel itself. Fission neutrons that maintained their original energies, i.e., were not slowed down in the graphite moderator, bombarded the abundant supply of non-fissioning 238U nuclei and triggered a nuclear reaction that transformed the 238U to 239Pu. The 239Pu could then be isolated through chemical extraction.

Following the initial operation of the X-10 Pile, Fermi’s visits to Oak Ridge were apparently infrequent, the last time in 1948. In September 1944, he inserted the first uranium fuel slug into the B Reactor at the Hanford Site, and on July 14, 1945, he observed the United States’ first test of a nuclear bomb (the Trinity test) only 25 days before the bomb was dropped on Hiroshima on August 6, 1945. He became a professor at the University of Chicago in July 1945 and continued an affiliation with Los Alamos National Laboratory. On November 28, 1954, he died of stomach cancer at the age of 53.

Operation of the X-10 Pile continued for 20 years with innumerable experiments being performed that provided valuable scientific data. Among the first was an experiment performed by Newson, Clifford and others to test a section of the proposed Hanford reactor shield. In late 1944, Clifford departed for Hanford and graduate school, but in 1947 he returned to Oak Ridge to the newly named Clinton National Laboratory, which in 1948 was renamed Oak Ridge National Laboratory.

Clifford soon became one of the pioneers in research aimed at understanding the penetration of radiation through materials proposed as reactor shields. The first facility for shielding experiments was built on the side of the X-10 Pile and utilized neutrons emitted through a 2-foot-square “core hole” that had been left in one side of the reactor shield. Clifford solicited my help in documenting some of the experiments, and thus began my career of recording nuclear research projects, primarily radiation shielding projects.

By the time the X-10 Pile was decommissioned in 1963, radiation shielding research in Oak Ridge had expanded to other facilities with Clifford remaining an important leader in its development. He ended his career in 1986, retiring from Princeton University where he worked on the university’s experimental nuclear fusion project. Again returning to Tennessee, he died in 2010 at the age of 90.

The genie that escaped the bottle in 1942 remains a subject of much debate, both with respect to the initial development and use of the nuclear bombs in 1945 and to the potential catastrophic effects that could be triggered by any one of the eight countries (or nine, Israel doesn’t say) who currently have nuclear arsenals. But, of course, the discovery of a sustained nuclear chain reaction was inevitable, if not in the United States, then elsewhere and in essentially the same time frame. And looking back over the 72+ years since it occurred, we can see that it initiated many other types of chain reactions with results that have benefited the world.

Probably the most important benefit has been the development of nuclear power plants. Currently, 30 countries utilize nuclear power, some as their primary source for producing electricity. Many countries, including the United States, are looking forward to newer small fail-safe nuclear power plants that will soon be tested. Although relatively unknown, the first electricity ever produced by nuclear power occurred at the X-10 Pile in 1948 when several engineers used steam produced by fission heat to generate enough electricity to light a single light bulb.

Also of immeasurable benefit has been the introduction of radioisotopes into the medical field and numerous industries. They were first produced in quantity in 1946, and, again, it was at the X-10 Pile. In that year Oak Ridge National Laboratory made more than a thousand shipments of radioisotopes, mostly iodine-131, phosphorus-32, and carbon-14.

For me personally, that first nuclear fission chain reaction had a tremendous positive effect. When the nuclear bombs ended World War II in 1945, I welcomed back most (not all) of my friends who had served in the Pacific Theatre, including my uncle who was present when Pearl Harbor was bombed. Approximately a year later I met another Pacific Theater survivor whom I married in May 1948. And, of course, a career path opened up to me that I could never have imagined. In effect, that first event initiated for me a personal chain reaction that took me in a very unexpected direction with highly beneficial results.

That is not to say that I have been oblivious to other chain reactions set in motion by that event that have led to less beneficial outcomes—some that have the potential for delivering world-wide disaster. I still remember bursting into tears when the word spread throughout Oak Ridge National Laboratory that President Truman had announced that Russia had detonated its first nuclear bomb on August 29, 1949. But it was not unexpected, above all not to those who had gathered with Fermi under the West Stands of Stagg Field or to the scientific community at large.

Dr. Alvin Weinberg, long-time director of Oak Ridge National Laboratory and probably my No. 1 scientist hero, spoke of the scientists’ dilemma in 1971. “We nuclear people have made a Faustian bargain with society,” he said. “On the one hand we offer … an inexhaustible source of energy. … But the price that we demand of society for this magical source is both a vigilance from and longevity of our social institutions that we are quite unaccustomed to.”

Although my young friend did not know of Enrico Fermi’s role in the first fission chain reaction, she and others in her generation are certainly aware of the benefits and responsibilities they have inherited from that event. Like those in earlier generations, they have faith that their own scientific pioneers will continue building on the benefits of nuclear research. And like those in earlier generations, they recognize that their overriding continuing responsibility is to ensure that mankind averts nuclear disaster. Failing in that responsibility is not an option!

 

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© 2019 Lorraine Swift Abbott

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