coordinate the efforts of the Corps, E.I. du Pont de Nemours,
and the Manhattan Project physicists. Indeed, the physicists had never before worked on such a large project. Under
wartime conditions and without the benefit of computers,
Groves drove the project forward with astonishing speed.
When B Reactor was activated, all seemed well at first. As
the hours passed, the reactor operators withdrew the control
rods in small increments, intending to increase the power output gradually to 250 MW. Whatever excitement surrounded
the start-up of the reactor faded quickly, however. After reaching 9 MW, the chain reaction began to lose momentum. By
6: 30 PM on September 27, it fizzled out completely.
The failure puzzled the Hanford staff members at first, but
they soon arrived at an explanation. A by-product of the fission of uranium, an isotope of xenon, was absorbing neutrons
at a high rate, disrupting the chain reaction. The physicists
determined that this effect, referred to as xenon poisoning,
could be overcome by introducing more neutrons—that is,
by adding more uranium fuel. Fortunately, previously unused
process tubes were available to receive the additional uranium.
If the reactor had been built as originally intended, it
would have had 1,500 process tubes, not nearly enough for
the amount of uranium needed to overcome xenon poisoning.
The available data suggested that number was sufficient. The
physicist John Wheeler, however, had expressed concern that
the reaction might create neutron-absorbing by-products.
George Graves, an engineer with E.I. du Pont de Nemours,
had given the matter considerable thought and insisted that
the pile include 2,004 tubes, just in case more fuel was needed. After the xenon poisoning incident, the B Reactor operators used every one of those tubes. Graves’s conservative design had spared the Manhattan Project a major setback.
The start-up of B Reactor was followed by the rapid
completion of two similar reactors, D and F. Soon the three
had produced enough plutonium to make the world’s first
atomic bomb, which the army detonated in a test in the
New Mexico desert on July 16, 1945. Meanwhile, the scien-
tists and engineers at Oak Ridge also had obtained success,
opening an alternative path to a weapon using uranium in-
stead of plutonium. Thus the first atomic bomb to be used in
warfare, the one dropped on Hiroshima, employed uranium
from Oak Ridge, whereas the second, which detonated over
Nagasaki, used plutonium from Hanford.
The use of atomic energy in warfare was an epochal event.
It was also a tragedy of catastrophic proportions, resulting in
at least 200,000 deaths and an inestimable number of other
harmful effects. The debate over whether the bombings were
justified continues, but one thing is clear: the Hanford B Reactor, along with the many other technological feats of the
Manhattan Project, changed history.
During the cold war the U.S. government continued to
expand the Hanford site, which grew to include nine nuclear
reactors, all of them water cooled and similar in design to B
Reactor. Over time, however, the demand for plutonium declined. Eight of the nine reactors, including B, had been decommissioned by 1971, and the last one was shut down in
1987. Operations at the Hanford site today focus not on production but on environmental remediation.
The Hanford B Reactor was listed in the National
Register of Historic Places in 1992 and was accorded landmark
status in ASCE’s Historic Civil Engineering Landmark Program
two years later. It will soon be in the national spotlight once
again. In the Carl Levin and Howard P. “Buck” McKeon National Defense Authorization Act for Fiscal Year 2015, Congress directed the U.S. Department of
Energy and the National Park Service to
establish the Manhattan Project National Historical Park by the end of this year.
The park is to include sites in Oak Ridge,
Los Alamos, and Hanford, including
B Reactor. —JEFF L. BROWN
Jeff Brown is a contributing editor to Civil
Twenty-nine vertical safety rods, each
35 ft long, hovered above the pile, ready
to drop and shut it down in an emergency.