Y-12: DESIGN
Oak Ridge: Clinton (1942-1943)
Events: The Uranium Path to the Bomb, 1942-1944

Although the Lewis Report had placed gaseous diffusion ahead of the electromagnetic approach, many were still betting in early 1943 that Ernest Lawrence (right) and his "calutron" would eventually predominate.  Lawrence and his laboratory of mechanics at the University of California, Berkeley, continued to experiment with the giant 184-inch cyclotron magnet, trying to reach a consensus on which shims, sources, and collectors to incorporate into the Y-12 Electromagnetic Plant that was to be built at Oak Ridge.  Research on magnet size and placement and beam resolution led Lawrence and his group in fall 1942 to propose an arrangement of huge electromagnetic coils connected by a bus bar in an oval racetrack configuration, as seen from above. Forty-eight gaps in the racetrack between the coils would each contain two vacuum tanks. With two racetracks per building, ten buildings would be necessary to provide the estimated 2,000 sources and collectors needed to separate 100 grams of uranium-235 daily.  The Berkeley researchers hoped that improvements in calutron design, or placing multiple sources and collectors in each tank, might increase efficiency and reduce the number of tanks and buildings required, but experimental results were inconclusive even as Stone & Webster of Boston, the Y-12 contractor at Oak Ridge, prepared to break ground.  

At a meeting of Leslie Groves (right), Lawrence, and John R. Lotz of Stone & Webster in Berkeley late in December 1942, Y-12 plans took shape.  It was agreed that Stone & Webster would take over design and construction of a 500-tank facility, while Lawrence's laboratory would play a supporting role by supplying experimental data.  By the time another summit conference on Y-12 took place in Berkeley on January 13 and 14, Groves had persuaded the Tennessee Eastman Corporation to sign on as plant operator and arranged for various parts of the electromagnetic equipment to be manufactured by the Westinghouse Electric and Manufacturing Company, the Allis-Chalmers Manufacturing Company, and the Chapman Valve Manufacturing Company.  General Electric agreed to provide electrical equipment.  

On January 14, after a day of presentations and a demonstration of the experimental tanks, Groves stunned the Y-12 contractors by insisting that the first racetrack of ninety-six tanks be in operation by July 1 and that 500 tanks be delivered by year's end.  Given that each of the five planned racetracks was 122 feet long, 77 feet wide and 15 feet high; that the completed plant was to consist of three 450-feet long buildings, each housing two racetracks placed end-to-end on the second floor; that tank design was in flux; and that separate chemistry buildings also would be needed for preparing charge materials and separating uranium recovered from the tanks, Groves's demands were little less than shocking.  Nonetheless, Groves maintained that his schedule could be met.

For the next two months Lawrence, the contractors, and the Army negotiated over the final design.  While all involved could see possible improvements, there simply was not enough time to incorporate every suggested modification.  Y-12 design was finalized at a March 17 meeting in Boston, with one major modification -- the inclusion of a second stage of the electromagnetic process.  The purpose of this second stage was to take the enriched uranium-235 derived from several runs of the first stage and use it as the sole feed material for a second stage of racetracks containing tanks approximately half the size of those in the first.  Groves approved this arrangement and work began on both the Alpha (first-stage) and Beta (second-stage) tracks.