Three Ways to Enrich Uranium at Oak Ridge: Y-12, K-25 and S-50

Oak Ridge, Tennessee, built three different plants to do one job: separate the lighter uranium-235 from heavier uranium-238 for atomic weapons. A National Park Service article on Manhattan Project science at Oak Ridge, a place that was called Kingston Demolition Range and Clinton Engineer Works during the project, explains how each plant worked and why two were wound down.

A sign at Oak Ridge during the Manhattan Project warning workers and residents to keep the project secret. Image from the U.S. Department of Energy.

Y-12: electromagnetic separation

The Y-12 Plant used electromagnetic isotope separation, developed by Berkeley scientist Ernest Lawrence. The idea is that lighter uranium-235 atoms move in a tighter circle than heavier uranium-238 atoms, so a vacuum tank with a strong magnetic field can split the atoms into two paths and capture them in separate containers. Lawrence made a mass spectrometer cyclotron, or calutron, at his Berkeley lab in late 1941, but Manhattan Project scientists decided a much larger facility was needed to make enough separated uranium-235 in time. Construction of Y-12 began on February 18, 1943.

The Beta racetrack at Y-12. Image from the U.S. Department of Energy.

At its peak Y-12 employed 22,000 people to run the calutrons, nicknamed "racetracks" for their oval shape. Because of a wartime labor shortage, young women, many just out of high school, were assigned to operate them, and became known as the "Calutron Girls." The article calls them vital to producing enriched uranium for the Little Boy bomb.

K-25: gaseous diffusion

K-25 was the largest building in the world at the time. It relied on over 3,000 gaseous diffusion steps through which uranium hexafluoride gas passed. Only the smaller uranium-235 atoms could pass through the tiny pores in each step's barrier, so the gas became more concentrated in uranium-235 at each step, much as smaller particles fall through a colander. Construction began in the fall of 1943 and it was in full operation by the spring of 1945. It made more enriched uranium at less cost, which led to many Y-12 calutrons being shut down by the end of 1946 and the loss of over 20,000 jobs.

An aerial photograph of K-25. Image from the U.S. Department of Energy.

S-50: liquid thermal diffusion

S-50 was meant as K-25's little sibling: it would slightly enrich uranium before K-25 enriched it further. It had 2,142 columns, each 48 feet high. It was built in record time, 69 days, but the process cost too much and used too much power for the enriched uranium it produced, and it was far less effective than K-25. It was deactivated in 1946.

An aerial photograph of S-50. Image from the U.S. Department of Energy.

The fourth facility

The X-10 Graphite Reactor did not enrich uranium. It was the first reactor built after the successful Chicago Pile experiment, and its job was to convert enriched uranium into plutonium for experimental purposes, something Hanford, Washington did at industrial scale. Plutonium samples from X-10 shipped to Los Alamos, New Mexico greatly influenced bomb design.

Despite their flaws, the article says, the enrichment plants working together were vital to the uranium-235 used in the Little Boy bomb dropped on Hiroshima on August 6, 1945, and together with X-10 they made the Manhattan Project a scientific success.

Sources

• National Park Service, Manhattan Project National Historical Park, "Manhattan Project Science at Oak Ridge," https://www.nps.gov/articles/000/manhattan-project-science-at-oak-ridge.htm; rewritten in hubnx's own words. A newspaper front page shown in the original is not reproduced, and the article's list of books is left out.