The Portsmouth Gaseous Diffusion Plant, or the "A-Plant" as the locals refer to it, broke ground on November 18, 1952. Earthmovers began leveling the rolling farmland for the building foundation the same day. One hundred thousand tons of structural steel, 14,500 tons of reinforcing steel in the concrete floors, 600 miles of process piping and 1,000 miles of copper tubing were used in the construction of the three process buildings. An additional 1,000 miles of tubing ran through the rest of the plant and
into the control rooms. Five hundred thousand cubic yards of concrete were required to complete the project. To support this, a separate concrete batching plant was constructed on plant site to serve all contractors. It produced 200 cubic yards of concrete per hour. It took 70 million man hours for construction.

The original estimate for construction was four years at a cost of $1.2 billion. Construction was carried out by Peter Kiewit and Sons of Nebraska at a cost of $750 million. The site was completed several months ahead of schedule at 34 percent below the original cost estimate at a $400 million savings. 

Operations began in 1954 while construction was ongoing with the plant coming fully online in early 1956 several months ahead of schedule. The primary mode of enrichment was the gaseous diffusion of uranium hexaflouride to separate the lighter fissile isotope, U-235, from the heavier non-fissile isotope, U-238. The plant initially produced material for the U.S. nuclear weapons program. In the mid-1960's, the plant converted to fuel production for commercial nuclear power plants. Portsmouth took material from Paducah that was enriched to 2.75% U-235 and further enriched it to approximately 4% and 5%. 

The plant enriched uranium from 1954 until 2001 through a process called gaseous diffusion. The 3,700-acre site in southern Ohio is owned and managed by the U.S. Department of Energy (DOE). The gaseous diffusion process is no longer operational
and DOE is conducting an extensive environmental cleanup of the site. A small number of inactive facilities have been removed and remaining structures, including the gaseous diffusion process buildings and support facilities, are being considered for demolition.


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