In the book, Hanford and the Bomb: An Oral History of World War II, author S. L. Sanger gives perhaps the most straightforward description of Hanford’s role in the Manhattan Project:
In simplest terms, Hanford’s job was to make plutonium inside the nuclear reactors by bombarding uranium fuel with neutrons, and to separate the plutonium from the irradiated uranium. The first step was nuclear; the second was chemical.
The first Hanford nuclear reactor (also known as atomic piles in the 1940s) in which the bombardment process took place was the B Reactor. After a fifteenth-month construction period, scientists and engineers began coaxing the B Reactor into operation in the fall of 1944. The B Reactor initially went critical on September 26, 1944. But getting the B Reactor into operational status was a lengthy, problematic exercise. Many of those problems were diagnosed and solved 70 years ago this month, in October 1944.
When you think of the Hanford reactors, imagine a roughly square box—36 ft. x 28 ft. x 36 ft.—of graphite with horizontal holes that function as tubes running through the box. In order to create a functioning reactor, the horizontal tubes are filled with cans—“slugs” in the nuclear business—of uranium. The nuclear reactor goes critical when enough uranium is placed inside the graphite box. If everything is properly controlled, the reaction is said to be self-sustaining.
The Hanford reactors were designed with 2,004 horizontal tubes. There were also a number of tubes for control rods, also mounted horizontally, that cut across the 2,004 tubes designed to contain uranium. The control rods, as the name implies, were used to control the level of neutron production within the pile and, therefore, the power production of the reactor. There were a few tubes drilled vertically through the reactor as well. These tubes could be used to shut down the reactor in an emergency. That way, in the event of the failure of the control rods, a last-ditch system consisting of a boron solution could be dumped over the pile from five 105-gallon tanks positioned on top of the reactor.
The amount of material and effort that went into the construction of the reactors is staggering. In his book The History and the Science of the Manhattan Project, physicist Bruce Cameron Reed has the following to say:
The piles themselves were welded to be gas-tight, and contained 2.5 million cubic feet of masonite; 4,415 t of steel plate; 1,093 t of cast iron; 2,200 t of graphite; 221,000 feet of copper tubing; 176,700 feet of plastic tubing; and some 86,000 feet of aluminum tubing.
As he had with the first atomic pile—CP-1—famously built under the stands of the University of Chicago’s former football field, Enrico Fermi loaded the first uranium slugs into the B Reactor at Hanford. This action, informally known as “the blessing of the pope,” took place on September 13, 1944. Loading of uranium continued until various measures of criticality took place on September 15-18.
In late September, power levels in the B reactor began to fluctuate because of the creation of the fission product xenon-135. The xenon-135 was capturing neutrons at a greater rate than had been predicted, and the resulting effect played havoc with the reactor’s ability to sustain a nuclear reaction. The solution turned out to be to add more uranium into more of the reactor’s tubes. The effect was discovered at many power levels. As a result, for much of October the engineers and scientists continued to add more uranium slugs to the reactor.
About the construction of Hanford as a whole, Reed says, “The total volume of land excavated at Hanford was equivalent to about 10% of that of the Panama Canal.” Though Hanford is almost entirely decommissioned now, the volume of radioactive waste that remains there makes it the most contaminated nuclear site in the United States.