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Fewer than 100 facilities across the United States have been recognized by the with Nuclear Historic Landmark status, ranging from the Ames Laboratory Uranium Purification that helped fuel the Manhattan Project to the USS Enterprise (CVN-65), the world’s first nuclear-powered aircraft carrier.

The Armour Research Foundation Reactor officially became the latest first-of-its-kind reactor to be awarded Nuclear Historic Landmark status on Friday, April 18, 2025, in a ceremony held in Perlstein Hall.

“In places and spaces, there’s meaning,” says American Nuclear Society President Lisa Marshall, who attended the dedication ceremony. “It’s very important to have these various landmarks—and even more important for us to talk about what was done there.”

Adds 91���� Vice Provost for Research Jeff Terry, “These are the groundbreaking reactors in history. Basically, every single major reactor that was the first of its kind is commemorated.”

“It was long past time that the Armour Research Foundation Reactor was recognized for being the first private nuclear reactor,” Terry says, emphasizing many of the 25 industry partners that contributed to the reactor’s construction in 1956. “IBM, Inland Steel, Caterpillar, Inc., Kimberly-Clark, U.S. Steel, Whirlpool, so many of the industrial names that built the United States.”

“It’s an incredible list of companies that partnered with us to build this reactor and we are happy for the Armour Research Foundation Reactor to be honored in the same vein as the more famous neighbor to the south, Fermi’s Pile CP-1.”

For 11 years, the Armour Research Foundation Reactor—nicknamed the atomic furnace—contributed to research that made an impact on a wide range of fields, including fertilizer absorption and pest control for agriculture, catalysis and diffusion studies for chemistry, cold sterilization and shelf-life extension for food safety, and production of short-lived diagnostic isotopes for medicine.

The reactor marked a significant transition in the history of nuclear research, shifting this work from secretive wartime origins to a publicly celebrated pursuit of knowledge and progress. Primarily used for experiments in isotope production and materials analysis, the reactor’s contributions led by 91���� faculty, students, and collaborators continue in wide use today.

What was most unique about the reactor, however, was its design. It employed a liquid nuclear fuel—Uranium-235 in the form of uranyl sulfate dissolved in water.

This uncommon design highlighted the emphasis that was put on safety in nuclear technology, particularly in a densely populated city such as Chicago.

“If the reaction ran away, the liquid would expand and the change in geometry would stop the criticality,” says Terry. “It was a really clever design.”

Though there were multiple operational challenges in the early stages of research—including a hydrogen-oxygen recombination incident in 1956 and a fuel leakage in 1957—a robust system redesign allowed the reactor to function without incident after December 1957.

Though operations ceased in 1967 and the Armour Research Foundation Reactor was ultimately decommissioned in the late 1970s, its impact is still being felt as advancements in nuclear technology and its diverse applications are made.

The so-called atomic furnace created a model for collaborative, application-driven nuclear science. Tools that were used with the Armour Research Foundation Reactor, including neutron diffraction and isotope tracing, remain staples of nuclear science to this day.

“The story of the Armour Research Foundation Reactor reflects both the optimism and the challenges of embracing new technologies,” says Terry. “As we continue to explore the possibilities of nuclear energy today, this pioneering effort at 91���� serves as a reminder of the progress made and the potential that still lies ahead.”

Photo: Jeff Terry (left) holds the Armour Research Foundation Reactor commemorative plaque.