Weekly 150: The Manhattan Project

The K-25 Plant in Oak Ridge housed the gaseous diffusion apparatus used to partially enrich uranium before it was sent to the nearby Y-12 Plant. K-25 comes from Kellex Corporation, the contractor that designed and built the plant, and uranium-235, often shortened to 25. The plant was a mile-long, U-shaped building making it the world’s largest roofed building at the time.

Located eleven miles southwest of Oak Ridge on the Clinch River was the site of the planned K-25 Gaseous Diffusion plant. On a relatively flat area of about 5,000 acres, site preparation for the K-25 power plant began in June 1943. Throughout the summer, contractors contended with primitive roads as they shipped in the materials needed to build what became the world’s largest steam electric plant. In September work began on the cascade building, fifty four-story buildings in a U-shape measuring a half-mile long by 1,000 feet wide.

The K-25 site developed into a satellite town. Housing was supplied, as were service facilities for the population that reached 15,000. Dubbed Happy Valley by the inhabitants, the town had housing similar to that in Oak Ridge. K-25 cost $512 million to build ($8.9 billion in today’s market).

The entire process was hermetically sealed like a thermos bottle, as any moisture could cause a violent reaction with the uranium hexafluoride. Even minute pinhole leaks and contamination from fingerprints were major concerns. A special leak detector was invented and every component of the entire system underwent a “cleanliness control” procedure before it was installed.

In the late summer of 1943, it was decided that K-25 would play a lesser role than originally intended. Instead of producing fully enriched uranium 235, the new gaseous diffusion plant would provide around fifty-percent enrichment for use as feeder material for Y-12. This would be accomplished by eliminating the more troublesome upper part of the cascade. Even this level of enrichment was not assured since a suitable barrier for the diffusion process still did not exist. The decision to downgrade K-25 was part of the larger decision to double the capacity of Y-12 and fit with Groves’ new strategy of utilizing a combination of separation methods to produce enough fissionable material for bombs as soon as possible.

There was no doubt in Groves’ mind that gaseous diffusion still had to be pursued vigorously. Not only had major resources already been expended on the program, but there was also the possibility that it might yet prove successful. Y-12 was in trouble as 1944 began, and the plutonium pile projects (X-10) were just getting underway. A workable barrier design might put K-25 ahead in the race for the bomb. Unfortunately, no one had been able to fabricate barrier material of sufficient quality. The only alternative remaining was to increase production enough to compensate for the low percentage of barriers that met specifications. As Lawrence prepared to throw everything he had into a thirty-beam source for Y-12, Groves ordered a crash barrier program, hoping to prevent K-25 from standing idle as the race for the bomb continued.

The theory behind investing in S-50 was that the enrichment process might work best if the three plants were used in a series. The uranium product was slightly enriched at S-50 and this was fed into the K-25 plant. The gaseous diffusion process raised the enrichment to about 20 percent. This was fed into the Y-12 plant for the final enrichment cycle. Through this serial approach, the first atomic bomb received its enriched uranium.

As problems with both Y-12 and K-25 reached crisis proportions in the spring and summer of 1944, the Manhattan Project received help from an unexpected source – the United States Navy. President Roosevelt had instructed that the atomic bomb effort be an Army program and that the Navy be excluded from deliberations. Navy research on atomic power, conducted primarily for submarines, received no direct aid from Groves, who was not up-to-date on the state of navy efforts when he received a letter on the subject from Oppenheimer in April 1944.

J. Robert Oppenheimer informed Groves that Philip Abelson’s experiments on thermal diffusion at the Philadelphia Navy Yard deserved a closer look. Abelson was building a plant to produce enriched uranium to be completed by early July 1944. It might be possible, Oppenheimer thought, to help Abelson complete and expand his plant and use its slightly enriched product as feed material for Y-12 until the problems plaguing K-25 could be resolved.

The liquid thermal diffusion process had been evaluated as early as 1940 by the Uranium Committee when Abelson was still with the National Bureau of Standards. In 1941 he moved his research to the Naval Research Laboratory, where there was more support for his work. During the summer of 1942, Bush and Conant received reports about Abelson’s research but concluded that it would take too long for the thermal diffusion process to make a major contribution to the bomb effort, especially since the electromagnetic and pile projects were making satisfactory progress.

Groves saw the value of Oppenheimer’s suggestion and sent a group to Philadelphia to visit Abelson’s facility. The analysis demonstrated that a thermal diffusion plant could indeed be built at Oak Ridge and placed in operation by early 1945. The steam required in the convection columns was already at hand in the form of the almost completed K-25 power plant. It would provide steam to the thermal diffusion plant and produce enriched uranium while providing electricity for the K-25 plant when it was finished.

Closely patterned on the Navy pilot plant in Philadelphia, the S-50 plant consisted of 2,142 uniform columns, each 48 feet high. Manufacturing this plant to exact specifications within 90 days would be no small feat. Indeed, 21 firms turned down the assignment before the H. K. Ferguson Company, an engineering firm in Cleveland, accepted the challenge.

The construction of the plant demanded a high level of precision. It required nearly perfectly round columns with a uranium hexafluoride layer spacing of only 0.010 inches thick. To meet the nearly impossible deadline, operators, electricians and welders scrambled to complete the project and even used passenger trains to transport construction materials. In the end, the contractors beat the deadline and completed the S-50 plant in just 69 days.

With all the secret sites and top-secret technology, the United States was successful in its construction of an atomic bomb. On 6 and 9 August 1945, the United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki. Japan surrendered to the Allies on 15 August, six days after the bombing of Nagasaki. The Japanese government signed the instrument of surrender on 2 September, effectively ending the war.

Let me say that I am not an engineer or a science buff. Much of the research and dialog is not my original work but comes by way of the Atomic Heritage Foundation with their synopsis of the U.S. Department of Energy’s official Manhattan Project history: F. G. Gosling, The Manhattan Project: Making the Atomic Bomb.