10 in. thick cast-iron base and a 23 ft thick concrete footing.
The design was based on that of Fermi’s Chicago pile and
a second experimental reactor at Oak Ridge. But because B
Reactor was so much larger than its predecessors, its design
presented new challenges.
One of those challenges was that the production of large
amounts of plutonium would generate intense heat. The Chicago reactor did not need a cooling system, but Hanford B
would self-destruct without one. Manhattan Project scientists and engineers debated the relative merits of various coolants, including water, helium gas, and even liquid bismuth.
Since it would not absorb neutrons, helium would not interfere with the nuclear reaction, but it would have to be stored
in huge airtight tanks and pumped through the pile under
extremely high pressure. Water, on the other hand, was an effective and familiar coolant, but it could oxidize the uranium
and interfere with the nuclear reaction.
In early 1943, the team finally decided to use purified Columbia River water. The cooling system they designed would
pump the water through tiny annular spaces to minimize its
effects on the nuclear reaction. In this way the amount of water in the pile would be limited to 400 gal at any given time.
The team also encased the fuel slugs in aluminum to prevent
uranium oxidation. The associated pump houses, water treatment facilities, and backup systems were so extensive that
they dominated the area surrounding the reactor.
Another challenge was the danger posed by radiation.
A 24 in. layer of graphite around the core of the pile would
provide some protection by deflecting neutrons back toward
the center. A 10 in. thick, water-cooled thermal shield made
up of interlocking cast-iron blocks also surrounded the pile.
Outside the thermal shield was an additional radiation shield
50 in. thick. It consisted of alternating layers of steel and Masonite, a readily available type of hardboard selected for its
high hydrogen content. Without such protection, anyone
near the pile would die within seconds.
The reactor stood inside building 105-B, a 53,750 sq ft behemoth of steel and reinforced concrete. It included a central
work area, a laboratory, a control room, a pool for the collection
and storage of irradiated uranium, and a dedicated railroad
track. Twenty-nine vertical safety rods, each 35 ft long, hovered
above the pile, ready to drop and shut it down in an emergency.
The obstacles to success were daunting. Nuclear technology was new. Only the purest materials could be used in the
pile. Any flaw in the structure of the reactor might render
it inoperable or even trigger a deadly disaster, so the reactor
had to be constructed with extreme precision. The need for
secrecy further complicated the project. Yet B Reactor went
into operation on September 26, 1944, just 15 months after
its construction began.
The completion of the reactor in such a short time was a
feat not only of nuclear engineering but also of construction
management. The enormous industrial plant was the first
of its kind, and its success depended on Groves’s ability to