Alpha calutron magnets are more than 20 feet tall.
For the first time ever, Y-12 is opening its original Pilot Plant — Building 9731 — to public viewing this weekend as part of the Secret City Festival in Oak Ridge, and some media members and a few Y-12 retirees got a preview of the facility this morning.
The tour included a look at the Pilot Plant’s Alpha calutrons, the only ones left in the world, as well as a couple of the Beta calutrons. The calutrons were used during the wartime Manhattan Project to test the electromagnetic separation processes used to separate the U-235 needed for the atomic bomb — Little Boy — ultimately dropped on Hiroshima, Japan.
In the photo at right, Y-12 historian Ray Smith stands in front of the Beta calutrons in Building 9731. For more information on the June 19 public tours of the facility, check out this site.

The calutrons in 9731 have been designated as Manhattan Project Signature Artifacts by the U.S. Department of Energy, and the building, which was completed in March 1943, is being considered for Historical Landmark status on the National Register of Historic Places.
Ultimately, there were 1,152 Alpha and Beta calutrons deployed at Y-12 during World War II to enrich the uranium needed for the atomic bomb. After the war, the enrichment role shifted to the K-25 plant, which came online late in the war effort and used a different method (gaseous diffusion) to separate the uranium isotopes.