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Feature Story | Argonne National Laboratory

The Physics Experiment That Changed The World

From Stagg Field to Supercomputers

Illustration by Rich Lo

On December 2, 1942, as World War II raged, a small group of scientists gathered beneath the football stands of the University of Chicago for a physics experiment that would very literally change the world.

In utmost secrecy, they had constructed a pile of uranium and graphite that would soon become the very first nuclear reactor. Led by Enrico Fermi, the scientists hoped to split uranium atoms and create the world’s first self-sustained, controlled chain reaction.

Seventy-six years later, the implications of that physics experiment still reverberate around the world. Besides shaping the outcome of the Second World War and the following half-century of international foreign policy, it has continued to shape the way the world views and uses energy, medicine, and scientific research.

The site of the world-changing physics experiment  — The University of Chicago’s Stagg Field in 1942.

CP-1, as the reactor was called, was not a particularly impressive engineering feat at first glance. It looked like a 20-foot-high mass of bricks; that’s where the name Chicago Pile-1,” or CP-1, came from. But it was actually 6 tons of uranium metal, 50 tons of uranium oxide, and 400 tons of graphite bricks laid in an arrangement painstakingly and precisely calculated by some of the greatest scientific minds in the country.

At 3:25 p.m., Fermi gave the final signal. The counters ticked, and the pile achieved criticality. The atomic age had begun.

As part of the nation’s Manhattan Project, Fermi’s team was expected to determine the likelihood that larger versions of CP-1 could breed plutonium to produce an atomic bomb. But greater plans for the discovery were already in place: the newly discovered atomic energy could be employed for peaceful uses, such as generating inexpensive electrical power.

That was the mission of Argonne — the lab that grew from Fermi’s experiment — when the federal government and the University of Chicago moved it west and designated it the first national laboratory in the United States.

The Atomic Energy Commission funded scientific work at Argonne, Oak Ridge, Brookhaven, and other national laboratories which led directly to the rise of nuclear power in America. The history of nuclear energy is a story of the partnership between government and science at its best. Virtually every nuclear reactor operating around the world today is based on technology and designs developed by U.S. national laboratories. 

It’s not often that we discover an entirely new way to produce electricity. The prospect required an enormous amount of scientific and engineering work, from developing the underlying theoretical physics calculations to creating materials that could withstand the intense conditions inside a reactor.

The Atomic Energy Commission also established a new site, the National Reactor Testing Station, in southern Idaho, far from densely populated areas, and developed a new Argonne branch, Argonne National Laboratory-West (now the Materials & Fuels Complex at Idaho National Laboratory) to build prototype reactors to test emerging ideas. 

In December 1951, Argonne’s Experimental Breeder Reactor-1 lit up four lightbulbs with the word’s first usable electricity from nuclear energy.

It was there, on December 20, 1951, just nine years after that wartime experiment in Chicago, that Argonne’s Experimental Breeder Reactor-I lit a string of four lightbulbs with the world’s first significant amount of electricity generated from nuclear power. The nuclear energy age was underway. 

Following preliminary design studies by Oak Ridge engineers, Argonne engineers designed and built a test reactor that Westinghouse and the U.S. Navy used to build the reactor for the first atomic-powered submarine, the USS Nautilus, which was launched in 1954. The Nautilus could run for 50,000 miles without refueling, and it became the first submarine to travel underneath the polar ice cap; its success demonstrated that nuclear power was both safe and reliable. In 1955, another test reactor in Idaho powered the entire nearby town of Arco. The next step was to prove the value of nuclear energy to utilities by producing electricity on a larger scale. Planning began for an operating prototype at Argonne, the Experimental Boiling Water Reactor. Commonwealth Edison watched closely, collecting data from the tests; the utility was poised to roll the reactor out for business if the tests were successful. 

In December of 1956, this reactor produced its first electricity, ramping up to produce 100 megawatts shortly thereafter. Soon Commonwealth Edison was building an almost identical reactor in nearby Dresden, Illinois, which would become the first large-scale power plant built entirely by private industry. The era of commercial-scale nuclear energy had truly begun. 

Over the following years, reactor research from the U.S. national laboratories became the basis for nearly every nuclear reactor around the world. The dominant types of nuclear reactors that power the world all have their origins in Argonne research,” says Laural Briggs, a nuclear engineer at Argonne.

For example, Argonne designed reactors and built and tested the early prototypes. Oak Ridge developed principles of reactor control and protection systems still used today. 

Today, more than 400 reactors provide about 11% of the world’s electrical power.1 The national laboratories continue to research and develop advanced nuclear reactors and how to handle spent nuclear fuel. They also work closely with the Nuclear Regulatory Commission to develop safety standards and practices, train industry professionals in the United States and abroad, and provide expertise on decommissioning older reactors. 

There were many other seismic shifts in the scientific landscape caused by the 1942 atomic chain reaction. The field of computer science, for example, broke through the surface as scientists built some of the first computers to model the physical phenomena — i.e., how the fuels were functioning and how the structural materials, which were under stress, were holding up — inside nuclear reactors.

Researchers can better solve thorny challenges, like those posed by nuclear physics, by breaking them down into smaller tasks. They tackle each with many processors that work together. This insight, known as parallel computing, lies at the heart of today’s supercomputers and the field of high-performance computing.

You have a lot of parameters to juggle. But high-performance computing can be very helpful” in the right circumstances, says Argonne’s Briggs. 

Merzari uses Argonne’s Mira supercomputer to conduct modeling and simulation experiments that have the potential to make nuclear reactors safer, more efficient, and economically more competitive.

That’s where Elia Merzari, principal nuclear engineer at Argonne, and his colleagues come in. Merzari is a member of an Argonne team that simulates how heat and fluids flow and create turbulence within nuclear reactors. To do this, the team must understand how heat and fluids behave under any simulated conditions — a field known as computational fluid dynamics.

We can simulate turbulence in great detail, thanks to the computing power of machines like the Mira supercomputer” located at the Argonne Leadership Computing Facility, says Merzari. 

To harness Mira’s full processing power, Argonne researchers developed an award-winning programming code, known as Nek5000. The code allows Mira to run on all cylinders to handle the largest-scale calculations for fluid flow in nuclear reactors,” says Merzari. 

The setup and the team’s expertise will ultimately help design a new generation of more economically viable reactors,” he says.

Take, for example, small modular reactors, a new concept for a self-contained source of nuclear power about as wide as a hot tub (one-quarter the size of a standard pressurized water reactor). These reactors could run nonstop for seven to 20 years and generate a total of 50 to 200 megawatts of power. They would be small and cost-effective enough to build in a factory and safely deliver to utility customers or scientific laboratories.

Researchers at Argonne and other U.S. national laboratories are refining the designs of these mini reactors by simulating via supercomputers how they might operate. This step can bolster safety, control costs, and promote efficiency because the researchers glean key insights before conducting real-world experiments. These benefits will multiply as Argonne and the other national laboratories move toward exascale, an era in which supercomputers will be 50 times faster than today. 

The chain reaction Fermi started that day in 1942 has gathered steam, rolled back scientific frontiers, and continues to improve our lives in surprising ways.

1 How Nuclear Power Helps Meet Global Energy Demand / The Role of  the IAEA, pub. IAEA Feb. 2017.

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