By Tim Bean

Just outside Chicago in the 1940s and 50s, visitors strolling down a wide and worn trail of the Red Gate Woods would suddenly stumble upon a gruff and well-armed garrison of military police. The MPs would pepper the confused strangers with questions, IDs would be checked, and pockets searched. Then without an apology or explanation, the confused visitors would be ordered firmly to leave how they came. And never come back.

Chicagoans wouldn’t learn for 10 or 20 years that they had stumbled upon the Manhattan Project’s Site A, codenamed Argonne. Here, the military housed the world’s first artificial nuclear reactor, CP-1 (Chicago Pile-1).


“Black bricks and wooden timbers”

Argonne’s nuclear reactor was technically Chicago Pile-2. CP-1 had been built and run in an abandoned racquetball court beneath the University of Chicago’s original Stagg Field in December of 1942. Envisioned by famous physicist Enrico Fermi CP-1, Chicago Pile-1 hardly seemed like the cutting edge of atomic science. This pile literally was a pile—330 tons of graphite bricks surrounding 5 tons of unrefined uranium metal. It was crude, ugly, and had no shielding to protect the scientists operating it. Fermi insisted the primitive clump of bricks would not produce enough energy to harm the scientists, the University of Chicago, or the City of Chicago. He was right. The world’s first controlled nuclear reaction ran less than five minutes at a half-watt of power. Not even enough to brighten the world’s smallest lightbulb. But it was a start.

Argonne and Site A

As the use of the Chicago Pile improved, concern for the safety of its operators (and the thousands of nearby students) promoted a move a few miles to the west, in the middle of the Forest Preserve District of Cook County, called Site A. The scientists dismantled CP-1, moved it to Site A, and reassembled it into a cube about 25 feet high and 30 feet on each base. This time, Fermi added a few safety elements. Five foot concrete walls surrounded its sides. Six inches of lead and 50 inches of lumber acted as a lid.

(Yes, wood. On a nuclear reactor.) 


Although assembled from Chicago Pile-1, this redesigned reactor had earned its own name, Chicago Pile-2. A year later, CP-3 joined CP-2, although 3 used heavy water instead of graphite to slow nuclear reactions. For a decade, scientists conducted hundreds of experiments using these primitive reactors. These experiments ranged from nuclear weapons to biomedical research to sustained nuclear energy. This site would first be known as the Metallurgical Laboratory, then the Argonne National Laboratory.

End of an Era

By 1954, the two reactors had become obsolete artifacts of nuclear energy’s early years. It was time to shut down. Engineers cannibalized useable parts or fuel for other reactors. The most radioactive and dangerous elements of the reactors were disposed of by the Oak Ridge Laboratory in Tennessee. The rest would be buried on site. Engineers dug a trench 40 feet long beside the former lab, encased the remains of CP-2 and CP-3 in concrete, and then rolled them into the trench to be entombed forever.


In the early and mid 1980s, amidst the horror of Three Mile Island and Chernobyl, the City of Chicago asked Greenpeace surveyors to test the burial grounds. They were horrified to find islands of radioactive elements dotting Site A, now called Site A/Plot M Disposal Site. Politely requesting help from the federal government did little good. When the information went public, however, the outcry was epic. People that had spent years strolling those woods, picnicking, and horseback-riding now found out it had been dangerously radioactive the entire time. The federal government gave the city $30 million to fence off, analyze, and decontaminate the site. A decade later their efforts transformed it into a safe, recreational area, although the site goes through a comprehensive survey annually.

Two markers now dominate the site. The first marks the site of the lab, and proudly states “We Built the World’s First Nuclear Reactor” followed by a summarized history of the Argonne. The second marks the location of the buried reactors describing the contents and size of the burial plot. At the top of the marker, four words are etched in deep, bold lettering, then underlined to further stress the point.


I’m removing an ad to share this warning: in researching this article, I witnessed a video of enterprising explorers using a long, thin pole to probe the burial site, hoping to find the entombed reactor itself.

Yeah, that’s a very bad idea.