S-50 Thermal Diffusion Plant

Secret Military Facilities - Summary…

S-50 was a third, much smaller plant built at Oak Ridge to help produce the highly enriched U-235 for the first atomic bomb.

Oppenheimer at Los Alamos learned in 1944 that the huge power house being built for the K-25 uranium enriching plant was going to be ready to produce high pressure steam almost six months before K-25 would need it. He suggested to General Groves that it be used to provide heat for a third enriching process called Liquid Thermal Diffusion. This process had been under development by the U.S.Navy and their pilot plant under construction in Philadelphia. It was copied and expanded many times over on the banks of the Clinch River next to the K-25 Powerhouse. Groves seized on every possible avenue to provide enriched feed material to Y-12’s Calutrons and thus shorten the war.

The S-50 plant was built in less than 70 days, starting up in September 1944. The amount of enriching it did was very important although it sounds small, only enriching from 0.7% U-235 to a little over 0.9%.

The S-50 plant fed this slightly enriched UF6 to Y-12 early, and then to K-25 when it got started in the early spring of 1945 where it was enriched further and then sent to Y-12. S-50 operated successfully, but was a far more difficult process to operate than either Y-12's or K-25's, so was shut down about a month after war's end and taken down soon after. It's cost was $16 million for capital and operations, and about 1,600 employees worked there at the peak.

In his memoirs, General K. D. Nichols tells that he had an estimate made of the value of the enriching done by S-50 during its year long operation. The assessment was that if it had not produced those thousands of pounds of slightly enriched uranium for Y-12, that Y-12 would have taken nine more days to deliver the required amount of product to Los Alamos. Nichols' comment was that considering the cost of the war ($250M/day) and the lives being lost each day, shortening the war by nine days seemed to him a good return on investment.

After the thermal diffusion process was no longer needed, the S-50 building became the location for the Nuclear Energy Powered Aircraft experiment until 1951 after which it was taken out of operation and demolished, becoming the first significant Manhattan Project facility to be decommissioned and demolished.

In depth: • ORNL Review - The First 50 Years - Chap. 2: High-Flux Years • Chap. 3: Accelerating Projects • Atomic Heritage Foundation