Qualla: K-25

K-25: Introduction

Sun, 22 Feb 2026 00:00:00 GMT

Photo credit ENERGY.GOV, Public domain. The building was so enormous that workers rode bicycles down its corridors. Built in 1944 at the Clinton Engineer Works in Oak Ridge, Tennessee, the K-25 gaseous diffusion plant surpassed the Pentagon as the largest building in the world, a four-story U-shaped structure covering over five million square feet. At peak construction, 25,000 workers swarmed the site -- and almost none of them knew what they were building. The codename said nothing: "K" came from Kellex, the engineering subsidiary that designed the plant, and "25" was wartime shorthand for uranium-235, the rare fissile isotope that makes up just 0.7 percent of natural uranium. The K-25 plant's job was to separate that sliver of an atom from its heavier sibling, uranium-238, one microscopic diffusion at a time, until there was enough enriched material to fuel a weapon. The enriched uranium it produced went into Little Boy, the atomic bomb dropped on Hiroshima on August 6, 1945.

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Image: ENERGY.GOV | Public domain

K-25: Splitting Atoms by the Trillions

Sun, 22 Feb 2026 00:00:00 GMT

Photo credit Department of Energy, Public domain. Gaseous diffusion exploits a simple physical principle: lighter gas molecules move slightly faster than heavier ones. Convert uranium into uranium hexafluoride gas, push it through a porous barrier with billions of microscopic holes, and the gas that passes through will be fracti...

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Image: Department of Energy | Public domain

K-25: The Barrier Nobody Could Build

Sun, 22 Feb 2026 00:00:00 GMT

Photo credit No machine-readable author provided. Aude assumed (based on copyright claims)., CC BY-SA 2.5. By August 1943, the entire K-25 project faced cancellation. The reason was the barrier. Without a membrane that could withstand uranium hexafluoride at industrial scale, gaseous diffusion was just a theory. Researchers at Bell Telephone Laboratories experimented with powdered nic...

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Image: No machine-readable author provided. Aude assumed (based on copyright claims). | CC BY-SA 2.5

K-25: Chrysler's Secret Assembly Line

Sun, 22 Feb 2026 00:00:00 GMT

Photo credit ENERGY.GOV, Public domain. The diffusers -- tank-like vessels that held the pressurized gas against the barrier membranes -- presented their own crisis. Building them from solid nickel would have consumed the nation's entire wartime supply of the metal. Groves handed the contract to Chrysler. Company presi...

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Image: ENERGY.GOV | Public domain

K-25: From Hiroshima to Obsolescence

Sun, 22 Feb 2026 00:00:00 GMT

Photo credit ENERGY.GOV, Public domain. Production at K-25 began in February 1945. The first shipments of slightly enriched product went to the Y-12 calutrons in March. By June the plant was producing material enriched to 7 percent; by September, 23 percent. The enriched uranium fed into the Little Boy bomb that devast...

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Image: ENERGY.GOV | Public domain

K-25: The Largest Demolition in History

Sun, 22 Feb 2026 00:00:00 GMT

Photo credit ENERGY.GOV, Public domain. Demolition of the K-25 complex was a project nearly as massive as its construction. Bechtel Jacobs received a $1.48 billion contract in 2008 to dismantle the main building. K-29 came down in 2006. K-33 followed in 2011. K-31 was demolished between 2014 and 2015. The original K-25...

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Image: ENERGY.GOV | Public domain