Chicago Pile-1 was the first nuclear reactor in the world to achieve a stable, self-sustaining nuclear chain reaction. It achieved this feat on 2 December 1942 and would lead to the development of nuclear power as a viable source of energy.
The reactor was constructed underneath a rackets court at the University of Chicago as part of the wider Manhattan Project and consisted of a large pile of uranium and graphite blocks assembled in a flattened ellipsoid shape.
The completed pile contained over 349,720 kilograms (771,000 pounds) of graphite, 36,555 kilograms (80,590 pounds) of uranium oxide and 5,625 kilograms (12,400 pounds) of uranium metal. Control of the pile’s reactions was achieved with a series of cadmium rods, which were inserted from the outside and absorbed neutrons. As such, withdrawing the rods would increase neutron activity, while inserting more would decrease it.
On 2 December 1942 the reactor went critical at 3.25pm, with lead scientist Enrico Fermi confirming the reactor was producing a self-sustaining reaction. The reactor remained operational for 28 minutes, producing 0.5 watts of energy (enough to power a small light bulb) before being shut down.
Following the success of Pile-1, it was deconstructed and moved to Red Gate Woods – the future site of the Argonne National Laboratory. More powerful reactors were built on the site and this research led to the invention of light and heavy water reactors, fast reactors and a large number of the designs that are used as the basis for today’s commercial reactors.
The pile’s pioneer
The Chicago Pile-1 was assembled under the supervision of famous Italian physicist Enrico Fermi. Fermi had been awarded the Nobel Prize in Physics four years previously for his work in induced radioactivity and began lecturing at Columbia University, NY.
In 1942 the laboratory group at Columbia, led by Fermi, was asked to move to the University of Chicago to work on the Manhattan Project (the research and development programme that would lead to the first atomic bomb) and it was from this work that the idea of constructing Chicago Pile-1 emerged.
The money to build the pile came from the US government itself, which on the back of a letter written by Albert Einstein and Leo Szilard, warning that Nazi Germany was attempting to develop an atomic bomb, led to President Roosevelt contributing USD 6,000 to the research.
Fermi took control of both the design and build, as well as running every calculation with meticulous detail. This led to a series of successful trial runs and, eventually, the now famous events of 2 December 1942.