The Manhattan Project: Making the Atomic Bomb

Decision on Pile Design

Greenewalt'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 slugs and tubes, and the one percent margin of safety fork. But he was even more worried about the proposed helium-cooled model. He feared that the compressors would not be ready in time for Hanford, that the shell could not be made vacuum-tight, and that the pile would be extremely difficult to operate. DuPont engineers conceded that Greenewalt's fears were well—grounded. Late in February, Greenewalt 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 for DuPont.

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