Scaling Up At Oak Ridge
Among results obtained with the 184-inch magnet was a design superior to it for large-scale calutrons, the so-called "XA." The prototype of the magnets to be installed at Oak Ridge, XA was a rectangular, three-coil magnet giving a horizontal field in which the calutron tanks could stand side-by-side. It had room for four alpha tanks, each with a double source. By the spring of 1943, convinced that the Germans might be ahead, General Leslie Groves decided to skip the scheduled pilot plant: procedures for alpha operation at Oak Ridge came from the XA and a scale model of the production magnet alone. Tests of the first full-scale system installed there, the XAX, were scheduled for July.
The spring and early summer of 1943 brought hundreds of trainees to Berkeley from Tennessee Eastman Company, the operator for the Oak Ridge plant. The Laboratory labored to ensure that the test XA magnet system and alpha units were working by April in spite of delays in delivery of steel. Between April and July the training sessions ran continuously. In June a migration that by 1944 would reach 200 started for Oak Ridge. Laboratory expenditures exceeded half a million dollars a month.
The first wave of Berkeley workers at Oak Ridge had to see that the XAX magnet worked. Then runs could begin on the first production system, or "racetrack;" a 24-fold magnification of the XA that could hold 96 calutron alpha tanks. To minimize magnetic losses and steel consumption, the assembly was curved into an oval 122 feet (37 m) long, 77 feet (23 m) wide and 15 feet (4.6 m) high. Want of copper for the large coils to produce the magnetic fields prompted a solution possible only in wartime: Groves borrowed 14,700 short tons (13,300 tonnes, 429 million troy ounces) of pure silver from a government vault for the purpose; all was later returned, the last few tons in 1970. Late in the summer of 1943 the XAX was ready for testing. After a week of difficulty, it cleared the hurdle for full-scale racetrack runs.
The first two of five projected racetracks started up in November and failed from contaminated cooling oil; the second was limping in January, but produced 200 grams of uranium enriched to 12 percent 235U by the end of February 1944, its fifth of the total goal of one kilogram of enriched uranium per month. By April four racetracks were functioning, including the repaired number 1. They required constant attention. Many people from the Laboratory helped modify the units to reach production goals.
The calutrons were initially operated by scientists from Berkeley to remove bugs and achieve a reasonable operating rate. Then Tennessee Eastman operators who had only a high school education took over. Kenneth Nichols compared unit production data, and pointed out to Ernest Lawrence that the young “hillbilly” girl operators were outproducing his Ph.Ds. They agreed to a production race and Lawrence lost, a morale boost for the Tennessee Eastman workers and supervisors. The girls were trained like soldiers not to reason why, while “the scientists could not refrain from time-consuming investigation of the cause of even minor fluctuations of the dials” Responsibility for operation passed entirely to Tennessee Eastman after the spring of 1944, and the Laboratory staff at Oak Ridge turned their attention to redesigning the calutron system for higher efficiency.
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