ORNL’s Gernot Rother of the American Chemical Society’s East Tennessee section, who served as master of ceremonies, watch as, from left, Sen. Randy McNally, Oak Ridge historian Ray Smith, ACS President Dorothy Phillips and Roane County Executive Wade Creswell unveil a prototype of a plaque marking the site of the former K-25 gaseous diffusion plant an ACS National Historic Chemical Landmark. Carlos Jones, ORNL/U.S. Dept. of Energy
In 1963, engineering student Harold Conner came to a site already steeped in history, hoping to be part of the next chapter.
Conner, the first black engineering major at West Tennessee’s University of Tennessee at Martin, started as a co-op student at Oak Ridge’s K-25 gaseous diffusion plant, where tens of thousands of people toiled in secret during World War II to enrich the uranium that would help put an end to the war.
“I didn’t know much about gaseous diffusion,” Conner said, “but I knew about Oak Ridge. I knew what they did, and suddenly here I am, and I’m a part of it. It was a pleasure and an honor.”
In his long career, Conner ultimately became site manager at K-25, then for all the government’s gaseous diffusion plants, and eventually executive vice president over U.S. uranium operations. Now 79, he still works as a consultant for government contractors and keeps up with his former K-25 coworkers from what he believes was a second “nuclear renaissance” in the 1960s, finding peacetime uses for enriched uranium.
On May 7, Conner joined other K-25 alumni, employees’ families, local dignitaries and ORNL leadership and staff, along with the general public, to honor K-25’s history and celebrate its potential as part of a third nuclear renaissance in East Tennessee.
They were present to witness the American Chemical Society awarding a National Historic Chemical Landmark designation to the development of the gaseous diffusion method for uranium isotope separation, which happened at K-25. That uranium was used in Little Boy, the atomic bomb the U.S. dropped on Hiroshima, Japan, in 1945.
After the war, work at the plant helped kick off an era of peacetime nuclear applications, fostering the use of isotopes for electricity, fuel for nuclear submarines, and medical imaging and treatments.
In an hourlong ceremony, the nonprofit unveiled a commemorative plaque that will be installed at the site, which sits to the west of the current Lab and is being redeveloped as an industrial park.
“As I stand here, I feel the weight of history all around,” said ACS President Dorothy Phillips. “It’s an honor to dedicate this National Historic Chemical Landmark in a place that represents not only remarkable scientific achievement but profound human dedication.”
Phillips said the designation honors both the scale of the science and the people who made it possible.
“The men and women who built this marvel were largely in the dark about their own creation,” Phillips said. “They showed up every day and did the work with focus, with care, and without the full picture. They drove to work each morning, passed through the security gates, and contributed pieces to a puzzle whose final image remained hidden from them.”
Then the largest building in the world, the original plant was built and operational in less than 20 months, with more than 25,000 people involved, said Oak Ridge historian Ray Smith, who spoke at the ceremony and wrote a detailed column about the effort for the Oak Ridger. There, uranium isotopes were separated by gaseous diffusion, a novel concept that required converting solid uranium into gas and then sending it through a cascade of nickel membranes, each with different-size holes through which the smaller U-235 molecules could pass. Each membrane enriched the uranium by only a tiny amount, requiring the connection of thousands of modules in cascades.
ORNL scientists played a large role in the development of processes and techniques to optimize enrichment, said Susan Hubbard, Deputy Director of Science and Technology, as well as in the peacetime applications that followed the war. Researchers at the Lab, the largest of the Department of Energy’s National Laboratory complex, were involved in the discovery of 11 elements on the periodic table; discovered the technique of neutron scattering, for which they were awarded a Nobel Prize; demonstrated for the first time that a research reactor can produce electricity; and delivered the first radioisotopes from a reactor for medical use.
The K-25 plant ceased operations in 1985. It was demolished in 2017.
But as part of its legacy, Hubbard noted, ORNL is the largest producer of isotopes in the Western world, providing more than 250 different isotopes for the needs of the U.S. its and allies. Their uses range from cancer treatment and medical imaging to securing ports and airports and powering deep space missions.
“This recognition is both apropos and timely, highlighting these historical accomplishments but coming at the time when there’s palpable excitement about enrichment and using the East Tennessee area to advance this important mission for the nation,” Hubbard told the audience of about 100. “East Tennessee has really been emerging as a strategic epicenter for this enrichment renaissance that we are seeing in the U.S.”
The region’s past accomplishments have attracted more than 150 nuclear companies to the area, she said, with more expected to be drawn by the Lab’s current work.
Besides developing new enrichment facilities to ensure the nation’s supply of stable isotopes, ORNL is advancing a variety of enrichment methods, including modern gaseous diffusion, electromagnetic isotope separation and plasma separation.
In addition, Hubbard said, the National Nuclear Security Administration has tapped ORNL to lead the development and deployment of small centrifuge technology that will go into a pilot facility within this decade. The centrifuge ultimately will be produced by private sector partners, with ORNL as the design authority.
“ORNL will be at the center, playing a vital role for making sure science and technology is as good as it can be for our domestic uranium enrichment needs in the nation for years to come,” Hubbard said. “It’s a very exciting time to look to the future in East Tennessee.”
This is the 90th National Historic Chemical Landmark designated by the ACS since the program’s start in 1992. It’s the second at ORNL; in 2008, the ACS recognized the production and distribution of radioisotopes for civilian research and medical use at the Oak Ridge National Laboratory in 1946.
The process was started by the late Wilber “Dub” Shults, retired director of ORNL’s Analytical Chemistry Division, who chaired the ACS East Tennessee section. It was taken up by a committee headed by Oak Ridge Associated Universities retiree Arlene Garrison.
The plaque will be displayed at the K-25 History Center, which opened to the public in 2020 on the property and has both artifacts and interactive exhibits. In addition, a Junior Ranger program lets students who visit the Manhattan Project National Historical Park and finish an activity book that includes K-25 history and chemistry earn a Junior Ranger Chemist badge. The first group of students, in collaboration with UT-Battelle, are set to complete the badge next week.
For Conner, whose career started at K-25, remembering the impact of his own years at the site makes him excited for its future.
“Many of us thought they’d never shut down K-25,” he said, “but they did, and with good reason, because we had enriched all the material we needed to for weapons and peacetime usage. So we were trying to find the next thing.”
Now, again, he’s eager to see what the “next thing” is for the remediated site – and for the nuclear industry.
“I like to say that I’ve been part of three nuclear renaissances,” Conner said. “I was born in 1946, during the first one. When I graduated college in 1968, the next 10 or so years, there was a second nuclear renaissance of sorts. And now, here we are in 2025, with another nuclear renaissance. Even though the facilities that I operated when I was here as a young engineer are gone, now you have new companies coming into the area, running new facilities.
“How about that? Three nuclear renaissances. It’s amazing.”
UT-Battelle manages ORNL for DOE’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States. DOE’s Office of Science is working to address some of the most pressing challenges of our time. For more information, visit energy.gov/science.
