History - Chicago Met Lab

The fall 1942 planning sessions at the Met Lab led to the decision to build a second Fermi experimental pile at Argonne as soon as his experiments on the first (CP-1) were completed and to proceed on design of the Mae West helium-cooled unit. When DuPont engineers assessed the Met Lab's plans in the late fall, they agreed that helium should be given first priority. They placed heavy water second and urged an all-out effort to produce more of this highly effective moderator. Bismuth and water were ranked third and fourth in DuPont's analysis.

Priorities changed when Fermi's calculations demonstrated a higher value of "k" than anyone had anticipated. Met Lab scientists concluded that a water-cooled pile was now feasible, while DuPont shifted its interest to air cooling. Since a helium-cooled unit shared important design characteristics with an air-cooled one, Greenwalt thought that an air-cooled semi-works at Oak Ridge would contribute significantly to designing the full-scale facilities at Hanford.

DuPont established the general specifications for the air-cooled semi-works and chemical separation facilities in early 1943. A massive graphite block, protected by several feet of concrete, would contain hundreds of horizontal channels filled with uranium slugs surrounded by cooling air. New slugs would be pushed into the channels on the face of the pile, forcing the irradiated ones at the rear to fall into an underwater bucket. The buckets of irradiated slugs would undergo radioactive decay for several weeks, then be moved by an underground canal into the separation facility where the plutonium would be extracted using remote control equipment.

Met Lab activities focused on designing a water-cooled pile for the full-scale plutonium plant. Taking their cue from the DuPont engineers, who utilized a horizontal design for the air-cooled semi-works, Met Lab scientists abandoned the vertical arrangement with water tanks, which had posed serious engineering difficulties. Instead they proposed to place uranium slugs sealed in aluminum cans inside aluminum tubes. The tubes, laid horizontally through a massive graphite block, would cool the pile with water injected into each tube, The pile, containing 200 tons of uranium and 1,200 tons of graphite, would need 75,000 gallons of fresh water per minute for cooling.

Pushing for a Decision on Pile Design

Greenwalt's initial response to the water-cooled design was guarded. He worried about pressure problems that might lead to boiling water in individual tubes, corrosion of the slugs and tubes, and the one-percent margin of safety for "k". But he was even more worried about the proposed helium-cooled model. He feared that the giant compressors would not be ready in time for Hanford to come on-line, that the shell could not be made vacuum-tight, and that the pile would be extremely difficult to operate. DuPont engineers conceded that Greenwalt's fears were well-founded. Late in February 1943, Greenwalt reluctantly concluded that the Met Lab's model, while it had its problems, was superior to DuPont's own helium-cooled design and decided to adopt the water-cooled approach.

The Met Lab's victory in the pile design competition came as its status within the Manhattan Project was changing. Still an exciting place intellectually, the Met Lab occupied a less central place in the bomb project as Oak Ridge and Hanford rose to prominence. Fermi continued to work on the Stagg Field pile (CP-1), hoping to determine the exact value of "k". Subsequent experiments at the Argonne site using CP-2, built with material from CP-1, focused on neutron capture probabilities, control systems, and instrument reliability. Once the production facilities at Oak Ridge and Hanford were underway, however, Met Lab research became increasingly unimportant in the race for the bomb and the scientists found themselves serving primarily as consultants to DuPont.

A Decision on Chemical Extraction

While the Met Lab physicists chafed under DuPont domination, a smoother and quieter relationship existed between the chemists and DuPont. Seaborg and Cooper continued to work well together, and enough progress was made in the semi-works for the lanthanum fluoride process in late 1942 that DuPont moved into the plant design stage and converted the semi-works for the bismuth phosphate method. DuPont pressed for a decision on plutonium extraction methods in late May 1943. Greenwalt chose bismuth phosphate, though even Seaborg admitted he could find little to distinguish between the two. Greenwalt based his decision on the corrosiveness of lanthanum fluoride and on Seaborg's guarantee that he could extract at least fifty percent of the plutonium using bismuth phosphate. DuPont began constructing the chemical separation pilot plant at Oak Ridge, while Seaborg continued refining the bismuth phosphate method.

It was now Cooper's job to design the pile as well as the plutonium extraction facilities at Clinton, both complicated engineering tasks made even more difficult by high levels of radiation produced by the process. Not only did Cooper have to oversee the design and fabrication of parts for yet another new Manhattan Project technology, he had to do so with an eye toward planning the Hanford facility. Safety was a major consideration because of the hazards of working with plutonium, which was highly radioactive. Uranium, a much less active element than plutonium, posed far fewer safety problems.

In July of 1942 Compton had established a new health division at the Met Lab and put Robert S. Stone in charge. Stone established emission standards and conducted experiments on radiation hazards, providing valuable planning information for the Oak Ridge and Hanford facilities.

END

Manhattan Project History

Manhattan Engineer District - The Beginning

Metallurgical Laboratory (Met Lab)

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