APS Historic Sites Initiative Recognizes the Chicago Pile “Site A” and Stagg Field at University of Chicago as Sites that Housed the World’s First Nuclear Chain Reaction

COLLEGE PARK, MD, July 13, 2023 – The American Physical Society has designated the Chicago Pile “Site A” and Stagg Field at the University of Chicago as Historic Sites to recognize the world’s first self-sustaining, controlled nuclear chain reaction. Each site will receive a plaque on July 14, 2023, acknowledging its exemplary contributions to physics.

“Few events have changed both science and society as greatly as the controlled nuclear fission research successfully performed by Fermi and his team at the University of Chicago,” said Lee Sawyer, chair of the APS Historic Sites Committee.

“Members of the APS Historic Sites Committee and I were frankly astounded that Stagg Field and associated sites such as Chicago Pile ‘Site A’ had not already been recognized. While the Stagg Field location is on the National Register of Historic Places as a ‘Site of First Self-Sustaining Nuclear Reaction,’ it had somehow never been nominated as an APS Historic Site. The committee quickly moved to remedy this, and to recognize this landmark in the history of physics.”

Added Juan de Pablo, executive vice president for science, innovation, national laboratories, and global initiatives at the University of Chicago: “The development of the world’s first controlled, sustained nuclear reaction at the University of Chicago defined a field of research and had a profound impact on world history, in ways that we continue to see today. We are honored by the American Physical Society’s recognition of the pivotal work that took place under the stands of the old Stagg Field and at the suburban ‘Site A,’ the forerunner of today’s thriving Argonne National Laboratory.”

In 1942, the Chicago Pile-1 nuclear reactor, which was built at the University of Chicago’s original Stagg Field, succeeded in triggering the first human-made, self-sustaining nuclear chain reaction. The reactor was moved in 1943 to Chicago Pile “Site A” in what is now the Cook County Forest Preserves. There, researchers continued to work with the reactor and its successors, leading to advances in nuclear energy, neutron scattering research and nuclear physics applications for medicine and other uses.

Following the site re-location, the Chicago Pile-1 fission reactor was referred to as Chicago Pile-2, including enhancement basics such as radiation shielding. The reactor used natural uranium and required an extraordinary amount of uranium to reach criticality. Graphite was used as the neutron moderator. Chicago Pile-2 was decommissioned in 1954. Chicago Pile-3 operated from 1943-1954 at Site A and has the distinction of being the first heavy water reactor in the world. It, too, was fueled by natural uranium and used heavy water as its neutron moderator. It first went critical on May 15, 1944. Due to aging concerns, the reactor was dismantled and rebuilt in 1950 with the new name of Chicago Pile 3-Prime.

Chicago Pile “Site A” can be considered one of the first large scale user facilities that gave inspiration to the many Department of Energy user facilities today. The site was released to the Cook County Forest Preserve District in 1956. The laboratory (subsequently named Argonne National Laboratory) relocated several miles northwest of “Site A.” The laboratory then assumed the role of principal reactor development center and continues to this day performing nuclear engineering research as one of its main activities. Today, at the end of the ¾ mile trail of Red Gate Woods, is the burial site of the world’s first nuclear reactors, technologies that launched the world into the Atomic Age and to building similar tools for enabling large-scale science.

The APS citation reads:

The Chicago Pile Site “Site A” is recognized for its transformational and impactful role in the development of nuclear energy, nuclear applications such as radioisotope production for medicine and research employing neutron scattering.

On 2 December 1942, a pivotal moment occurred at CP-1. Enrico Fermi led the world's first self-sustaining nuclear chain reaction, a remarkable achievement. The reactor's construction took place under Stagg Field's west viewing stands by the talented team from the University of Chicago's Metallurgical Laboratory.