Milwaukee. Solid-silver bus bars a square foot in cross section crowned each racetrack's long oval. The silver was worth more than $300 million. Groves accounted for it ounce by ounce, almost as carefully as he accounted for the fissionable isotope it helped separate.
Stone & Webster had only foundation drawings in hand when its contractors broke ground for the first Alpha racetrack building on February 18, 1943. Groves had initially approved three buildings to house five racetracks. In March he authorized a second, Beta stage of half-size calutrons, seventy-two tanks on two rectangular tracks, that would further enrich the eventual Alpha output to 90 percent U235. Alpha and Beta buildings alone eventually covered more area in the valley between Pine and Chestnut ridges than would twenty football fields. Racetracks were mounted on second floors; first floors held monumental pumps to exhaust the calutrons to high vacuum, more cubic feet of vacuum than the combined total volume pumped down everywhere else on earth at that time. Eventually the Y-12 complex counted 268 permanent buildings large and small — the calutron structures of steel and brick and tile, chemistry laboratories, a distilled water plant, sewage treatment plants, pump houses, a shop, a service station, warehouses, cafeterias, gatehouses, change houses and locker rooms, a paymaster's office, a foundry, a generator building, eight electric substations, nineteen water-cooling towers — for an output measured in the best of times in grams per day. An inspection trip in May 1943 awed even Ernest Lawrence.
By August, twenty thousand construction workers swarmed over the area. An experimental Alpha unit saw successful operation. Lawrence was urging Groves then to double the Alpha plant. With ten Alpha racetracks instead of five he estimated he could separate half a kilogram of U235 per day at 85 percent enrichment. An Army engineer's less exuberant summary, written six days after Lawrence's, predicted 900 grams per month with existing Alpha and Beta stages beginning in November 1943, for a total of 22 kilograms of bomb-grade U235 in the first year of operation. Faced with new estimates from Los Alamos that summer that an efficient uranium gun would probably require 40 kilograms — 88 pounds — of the rarer uranium isotope, Groves bought Lawrence's proposal. The doubling would add four new 96-tank tracks of advanced design designated Alpha II and a proportionate number of Beta tracks, at a cost of $150 million more than the $100 million already authorized. If everything worked at Y-12, Groves justified his proposal to the Military Policy Committee, he would then have a 40-kilogram bomb core around the beginning of 1945.
The Army had contracted with Tennessee Eastman, a manufacturing subsidiary of Eastman Kodak, to operate the electromagnetic separation plant. By late October 1943, when Stone & Webster finished installing the first Alpha racetrack, the company had assembled a work force of 4,800 men and women. They were trained to run and maintain the calutrons — without knowing why — twenty-four hours a day, seven days a week.
The big square racetrack magnets wrapped with silver windings were encased in boxes of welded steel. Oil that circulated through the boxes was supposed to insulate the windings and carry heat away. The first magnets tested at the end of October leaked electricity. If moisture in the circulating oil was shorting out the coils, the normal heat of operation would correct the problem by evaporating the water. Tennessee Eastman pushed on. Vacuum leaks in the calutron tanks were numerous and hard to find — one supervisor remembers spending most of a month looking for one leak. Inexperienced operators had trouble striking and maintaining a steady ion beam. Groves recalls that the powerful magnets unexpectedly “moved the intervening tanks, which weighed some fourteen tons each, out of position by as much as three inches… The problem was solved by securely welding the tanks into place, using heavy steel tie straps. Once that was done, the tanks stayed where they belonged.”
The magnets dried out but continued to short. Something was seriously wrong. Early in December Tennessee Eastman shut the entire 96-tank racetrack down. The company's engineers would have to break open one of the windings and examine it. That was major trauma; the unit must then be returned to Allis-Chalmers and rebuilt.
The inspectors found disaster: two major troubles. “The first lay in the design,” writes Groves, “which placed the heavy current-carrying silver bands too close together. The other lay in the excessive amount of rust and other dirt particles in the circulating oil. These bridged the too narrow gap between the silver bands and resulted in shorting.” Groves arrived seething from Washington on December 15 to view the remains. The design's inadequacy forced the general to order all forty-eight magnets hauled back to Milwaukee to be cleaned and rebuilt. The second Alpha track would not come on line until mid-January 1944. They would lose at least a month of production.
Tennessee Eastman's 4,800 employees reported for work in the shambles of gloomy halls. Rather than lose them from boredom the company scheduled classes, conferences, lectures, motion pictures, games. Serious men in double-breasted suits scouted the state for chess and checker sets. At the end of 1943 Y-12 was dead in the water with hardly a gram of U235 to show for all its enormous expense.
Gaseous-diffusion research had progressed at Columbia University since John Dunning and Eugene Booth had first demonstrated measurable U235 separation in November 1941. By the spring of 1942 Harold Urey could note in a progress report that “three methods for the separation of the uranium isotopes have now reached the engineering stage. They are the English and the American diffusion methods, and the centrifuge method.” With the authorization of the full-scale plant Dunning's staff, which had grown to include about ninety people, increased in early 1943 to 225. Franz Simon's diffusion method would have operated at low gas pressures and in incremental ten-unit stages but required extremely large pumps; Columbia designed a high-pressure system with more conventional pumps, a continuous, interconnected cascade of some four thousand stages. In a postwar memoir Groves reviews the design, which was both reliably simple and expensively tedious:
The method was completely novel. It was based on the theory that if uranium gas was pumped against a porous barrier, the lighter molecules of the gas, containing U-235, would pass through more rapidly than the heavier U-238 molecules. The heart of the process was, therefore, the barrier, a porous thin metal sheet or membrane with millions of submicroscopic openings per square inch. These sheets were formed into tubes which were enclosed in an airtight vessel, the diffuser. As the gas, uranium hexafluoride, was pumped through a long series, or cascade, of these tubes it tended to separate, the enriched gas moving up the cascade while the depleted moved down. However, there is so little difference in mass between the hexafluoride of U-238 and TJ-235 that it was impossible to gain much separation in a single diffusion step. That was why there had to be several thousand successive stages.
In schematic cross section the stages looked like this:
“Further development of barriers is needed,” Urey had concluded in his progress report, “but we now feel confident that the problem can be solved.” It had not been solved when Groves committed the Manhattan Project to a $100 million gaseous-diffusion plant, however; no practical barrier was yet in hand. The American process required finer-pored material than the British; the material also had to be rugged enough to withstand the higher pressure of the heavy, corrosive gas.
Columbia had been experimenting with copper barriers but abandoned them late in 1942 in favor of nickel, the only common metal that resisted hexafluoride corrosion. Compressed nickel powder made a suitably rugged but insufficiently fine-pored barrier material; electro-deposited nickel mesh made a suitably fine-pored but insufficiently rugged alternative. A self-educated Anglo-American interior decorator, Edward Norris, had devised the electro- deposited mesh originally for a new kind of paint sprayer he invented; he joined the Columbia project in 1941 and worked with chemist Edward Adler, a young Urey protege, to adapt his invention to gaseous diffusion. The resulting Norris-Adler barrier in its nickel incarnation seemed in January 1943 to be improvable eventually to production quality, whereupon Columbia began installing a pilot plant in the basement of Schermerhom Laboratory and Groves authorized full-scale barrier production. The Houdaille-Hershey Corporation took on that assignment on April 1, the day the gates began operating at Oak Ridge, planning a new factory for the purpose in Decatur, Illinois.
Suitable barrier material was the worst but not the only problem Columbia studied and Groves engineered. Hex attacked organic materials ferociously: not a speck of grease could be allowed to ooze into the gas stream anywhere along the miles and miles of pipes and pumps and barriers. Pump seals therefore had to be devised that were both gastight and greaseless, a puzzle no one had ever solved before that required the development of new kinds of plastics. (The seal material that eventually served at Oak Ridge came into its own after the war under the brand name Teflon.) A single pinhole leak anywhere in the miles of pipes would confound the entire system; Alfred O. Nier developed portable mass spectrometers to serve as subtle leak detectors. Since pipes of solid nickel would exhaust the entire U.S. production of that valuable resource, Groves found a company willing to nickel-plate all the
