Argonne at 50

Chicago Pile reactors create enduring research legacy

But open houses are nothing new at Argonne. The laboratory's first open house, held March 20, 1954, brought some 2,300 people -- mostly employees and their families -- to the laboratory to tour Chicago Pile 5 (CP-5), the nation's newest nuclear reactor.

Like the Advanced Photon Source, CP-5 was a powerful -- for its time -- research machine. But instead of X-rays, it used neutrons -- uncharged particles found in the nuclei of nearly all atoms. And while it was used for a good deal of materials research starting in the 1970s, its major mission was to study the physics of atomic nuclei.

During its 25-year career, CP-5 attracted hundreds of scientists from industry, universities and government laboratories all over the world. It opened new horizons in nuclear physics and materials research. It taught future scientists, trained reactor operators, and served as a model for many other research reactors in the United States and abroad.

CP-5 was the fifth and last member of the distinguished family of "Chicago Pile" reactors, whose legacy ranges from the earliest efforts to develop nuclear reactors to current environmental research aimed at learning how to retire them safely.

Chicago Pile 1 was the world's first nuclear reactor, built in 1942 by Enrico Fermi under the abandoned football stands at the University of Chicago.

Early in 1943, CP-1 was dismantled and moved to a less-populated site in the "Argonne Forest" section of the Cook County Forest Preserve in Palos Park. That part of the forest has since been renamed, but its appellation survives today in the name of Argonne National Laboratory.

Fermi's reactor was rebuilt in a new configuration and redubbed CP-2. A small laboratory atop the 14,000-ton reactor provided space for limited experiments using neutrons from the reactor's core. The reactor's face contained ports through which materials could be inserted into the core for irradiation.

Chicago Pile 3, a research reactor built in the Argonne Forest in 1944, was the world's first "heavy-water moderated" reactor . Today, 35 heavy-water reactors around the globe generate more than 18 million megawatts of electricity.

The core of a heavy-water moderated reactor is surrounded by water in which normal hydrogen atoms have been replaced by deuterium, a heavier form of the element. Inside the reactor core, uranium atoms split to release neutrons, which strike other uranium atoms, causing them to split in turn and creating a chain reaction. If the neutrons move too fast, they are less likely to split uranium. The moderator's job is to slow them down.

There is no "Chicago Pile 4" in the CP lineage. That's because the reactor that was called "CP-4" in its early design stages eventually became Experimental Breeder Reactor I (EBR-1). Today, EBR-1 is a Registered National Historic Landmark in recognition of its many historical firsts:

• First reactor built at the National Reactor Test Station (known today as the Idaho National Engineering Laboratory).

• First reactor to generate usable amounts of electricity, powering a string of four light bulbs on Dec. 20, 1951.

• First reactor to demonstrate the "breeder principle," which allows a reactor to create more fuel than it burns.

When Chicago Pile 5 retired from active service as a materials research reactor in 1979, it marked the end of operations for the Chicago Pile reactors.

But today, CP-5 is the site of a new program to develop new technologies to safely decontaminate and decommission aging facilities. With this program , the Chicago Pile legacy has come full circle, from pioneering nuclear reactors 50 years ago to learning how to retire them safely today.

For more information, please contact Steve McGregor (630/252-5580 or media@anl.gov) at Argonne.