DuPont broke ground for the X-10 complex at Oak Ridge in February
1943. The site would include an air-cooled experimental pile
reactor, a pilot chemical separation plant, and various support
facilities. Cooper produced blueprints for the chemical separation
plants in time for construction to begin in March. A series of
huge underground concrete cells, the first of which sat under the pile,
extended to one story above ground. Aluminum cans containing
uranium slugs would drop into the first cell of the chemical separation
facility and dissolve and then begin the extraction process.
The pile building itself went
up during the spring and summer of 1943, a huge concrete shell seven
feet thick with hundreds of holes for uranium slug placement.
Slugs were to plutonium piles what barrier was to gaseous diffusion;
that is, an obstacle that could shut down the entire process.
ALCOA (Aluminum Company of America) was the only firm left working on a
process to enclose uranium 235 within aluminum sheaths, and it was still
having problems. Initial production provided mixed results, with
many cans failing vacuum tests because of faulty seams.
The moment everyone had been
waiting for came in late October 1943 when DuPont completed construction
and tests of the X-10 pile. After thousands of uranium slugs were
loaded, the pile went critical in the early morning of November 4th and
produced its first plutonium by the end of the month. Criticality
was achieved with only half of the channels filled with uranium.
During the next several months, Compton gradually raised the power level
of the pile and increased plutonium yield.
techniques using the bismuth phosphate process were so successful that
Los Alamos received its first plutonium samples beginning in the spring
of 1944. Fission studies of these samples at Los Alamos during the
summer heavily influenced bomb design.