History - Chicago Met Lab

Webmaster's Note: The Metallurgical Laboratory at the University of Chicago played a prominent role in forging ahead with breaking technology during the years leading up to the official formation of the Manhattan Project. Not only did Fermi successfully carry out his pile experiments here, but Glenn Seaborg carried out his research on Plutonium separation and concentration, while other brilliant physicists such as Leo Szilard, James Franck, Eugene Wigner, and Walter Zinn worked tirelessly on theoretical studies contributing to the formal approval of the Project.

However, once the Project moved from the conceptual stage to the design and construction stage, the role of the Met Lab changed to that of a supporting laboratory. In fact many of the prominent scientists relocated to other locations for the duration of the project. Some, such as Fermi, worked at Oak Ridge, Hanford and eventually Los Alamos as scientific expertise requirements constantly changed.

One of the most important branches of the far-flung Manhattan Project was the Metallurgical Laboratory at the University of Chicago. Known as the Met Lab, its primary role was to design a production pile to produce plutonium. Here again the job was to design equipment for a technology that was not well understood even in the laboratory. The Fermi pile, important as it was historically, provided little technical guidance other than to suggest a lattice arrangement of graphite and uranium. Any pile producing more power than the few watts generated by Fermi's famous experiment (CP-1) would require elaborate controls, radiation shielding, and a cooling system. These engineering features would all contribute to a reduction in neutron multiplication (neutron multiplication being represented by "k"); so it was imperative to determine which pile design would be safe and controllable and still have a k high enough to sustain a chain reaction.

A group headed by Compton's chief engineer, Thomas V. Moore, began designing the production pile in June 1942. Moore's first goals were to find the best methods of extracting plutonium from the irradiated uranium and for cooling the pile.

Webmaster's Note: The entire process of a chain reaction in uranium producing plutonium is of course a very complex procedure. However, for the "everyday" person trying to better understand, I offer the following simplified explanation:

Blocks of uranium and a moderator, such as graphite, are assembled (stacked) in a "pile" until enough neutrons are emitted to sustain a chain reaction.

This chain reaction continues unabated and essentially "cooks" the uranium, producing energy. As a by-product, this cooking also transmutes some of the uranium atoms to form another element: plutonium.

After a certain number of days "cooking", the irradiated uranium blocks (now containing some plutonium) are removed from the pile.

This irradiated uranium now undergoes a chemical extraction process where the plutonium is removed and purified.

One major hurdle: The extracted plutonium is highly radioactive. Therefore the removal of the irradiated uranium and the extraction of the plutonium would have to accomplished using remote control equipment.

It quickly became clear that a production pile would differ significantly in design from Fermi's experimental reactor (CP-1), possibly by extending uranium rods into and through the graphite next to cooling tubes and building a radiation and containment shield. Although experimental reactors like Fermi's did not produce enough power to need a cooling system, piles built to produce plutonium would operate at high power levels and require coolants. The Met Lab group considered the full range of gases and liquids to isolate the substances with the best nuclear characteristics, with hydrogen and helium standing out among the gases and water, even with its tendency to corrode uranium, as the best liquid.

During the summer, Moore and his group began planning a helium-cooled pilot pile for the Argonne Forest Preserve near Chicago, built by Stone & Webster, and on September 25 they reported to Compton. The proposal was for a 460-ton cube of graphite to be pierced by 376 vertical columns each containing twenty-two cartridges of uranium and graphite. Cooling would be provided by circulating liquid helium from from top to bottom through the pile. A wall of graphite surrounding the reactor would provide radiation containment, while a series of spherical segments that gave the design the nickname Mae West would make up the outer shell.

By the time Compton received Moore's report, he had two other pile designs to consider. One was a water-cooled model developed by Eugene Wigner and Gale Young, a former colleague of Compton's. Wigner and Young proposed a twelve-foot by twenty-five foot cylinder of graphite with pipes of uranium extending from a water tank above, through the cylinder, and into a second tank of water underneath. Coolant would circulate continuously through the system, and corrosion would be minimized by coating interior surfaces or lining the uranium pipes.

A second alternative to Mae West was more daring. Szilard thought that liquid metal would be such an efficient coolant that, in combination with an electromagnetic pump having no moving parts (adapted from a design he an Einstein had invented), it would be possible to achieve high power levels in a considerably smaller pile. Szilard had trouble obtaining supplies for his experiment, primarily because bismuth, the metal he preferred as the coolant, was very rare.

Manhattan Project History

Manhattan Engineer District - The Beginning

Metallurgical Laboratory (Met Lab)

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