K-25 is a former uranium enrichment facility of the Manhattan Project

Manhattan Project

The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...

 which used the gaseous diffusion

Gaseous diffusion

Gaseous diffusion is a technology used to produce enriched uranium by forcing gaseous uranium hexafluoride through semi-permeable membranes. This produces a slight separation between the molecules containing uranium-235 and uranium-238 . By use of a large cascade of many stages, high separations...

 method. The plant is located in Oak Ridge, Tennessee

Oak Ridge, Tennessee

Oak Ridge is a city in Anderson and Roane counties in the eastern part of the U.S. state of Tennessee, about west of Knoxville. Oak Ridge's population was 27,387 at the 2000 census...

, on the southwestern end of the Oak Ridge Reservation.
The code name "K-25" was a combination of the "K" from the Kellex Corporation, the initial contractors of the plant, and a World War II-era code designation for uranium-235

Uranium-235

- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...

.

Begun in June 1943 and completed in early 1945 at a cost of $512 million (equivalent to $ in today dollars), the K-25 plant employed 12,000 workers.