Manhattan Project Science at Hanford

Aerial photo of plutonium reactor complex with buildings and stacks
Hanford's B Reactor in operation, January 1945

Department of Energy

The Manhattan Project, America’s wartime effort to build an atomic bomb, was so promising, yet so unlikely to succeed, that two independent paths were followed, in the hopes that at least one of them would produce a war-changing bomb.

One of those methods was based on using carefully refined uranium as the heart of the bomb. That work was done at Oak Ridge, Tennessee. The second method was based on the recently discovered element, plutonium. But unlike uranium, plutonium was almost nonexistent in nature, but could be manufactured. And that job would be done at the Hanford Engineer Works (the Hanford site), in the desert of southeastern Washington state.

The manufacturing process at Hanford was developed from what Enrico Fermi and his team proved when they constructed the world’s first, albeit small-scale, nuclear reactor in Chicago in 1942. If a reactor could be built sufficiently large, the intense flow of neutrons within it could, almost magically, change uranium into plutonium. This process of transmutation would not be creating gold from straw or lead, but would be creating something much more valuable.
Black and white overhead view of workers in the reactor core
Workers stacking graphite blocks in the reactor core

Department of Energy

To that end, the Army Corps of Engineers took over more than 500 square miles of land, including the towns of Hanford, White Bluffs, and Richland, in Washington state. The vast, remote site was bordered by the Columbia River, a critical resource for cooling in the manufacturing process, with vast amounts of cool and relatively pure water. The process at Hanford involved three steps.

First, many tons of uranium would be formed into 8.7-inch rods, about an inch and a half in diameter. Each was then clad in aluminum, like being canned. The result was commonly referred to as a fuel slug, tens of thousands of which would be needed for the next step of the process.

Three nuclear reactors were built at Hanford, each basically a copy of the others. The brand-new and unproven technology was so uncertain that building three would increase the odds of at least one succeeding. At the core of each reactor was a huge matrix of graphite blocks, measuring 36 feet by 36 feet by 28 feet front to back, and enclosed in five feet of heavy shielding. From front to back ran 2004, 1.7-inch aluminum tubes, into which were loaded more than 60,000 uranium fuel slugs. All-important cooling water would flow in the narrow space between the slugs and the aluminum tube. It was Hanford’s B Reactor that was the first reactor to be built and then loaded with fuel slugs. When the operators withdrew the control rods, the nuclear chain reaction began, and the world’s first full-scale nuclear reactor went into service on September 26, 1944.

Aerial photo of open expanse with sparse nuclear buildings throughout
Hanford west area, December 1944

Department of Energy

In the midst of the intense nuclear chain reaction in the reactors, some neutrons would merge with uranium atoms, which would eventually produce atoms of plutonium—the transmutation process.

After a sufficient time in the operating reactor, fuel slugs would be pushed out the back of the reactor into a deep pool of water, which would cool them while also protecting the workers from the intense radiation they produced. After a period of time, the fuel slugs would be transported in heavily shielded railroad cars across the Hanford site, for the third step in the manufacturing process.

This was the chemical-processing plant, where the highly radioactive reactor fuel would be treated in batches of about 3000 kg. The fuel would be dissolved in acid and then put through a series of chemical processes that eventually extracted a small amount of plutonium—a very small amount. In 3000 kg of uranium, perhaps three-quarters of a kilogram (750 grams) of plutonium would be produced (0.025 percent). So, what happened to the rest of each batch?

In the early days at Hanford, everything that wasn’t plutonium would be dumped into underground storage tanks, to be dealt with only when the urgency of the war ended (and is still being dealt with today). Along with the original uranium and aluminum cladding, there were by-products of the nuclear fission process, many of which were quite radioactive. There were also the chemicals that had been used in the various steps of the process. All in all, the mix of metals, chemicals, and radioactivity in the waste at Hanford created a serious and very expensive clean-up process, still being dealt with 75 years later.

Finally, when a sufficient amount of plutonium had been produced, it was carefully and secretly shipped to the Manhattan Project site at Los Alamos, New Mexico. There, scientists, engineers, and craft workers designed and built the world’s first atomic bomb from Hanford plutonium, which was successfully detonated in the Trinity test, in New Mexico, on July 16, 1945. A few weeks later, on August 6, the Little Boy bomb, as it was called, which was built from Oak Ridge uranium, was detonated over the Japanese city of Hiroshima. And then, on August 9, 1945, Hanford plutonium exploded in the Fat Man bomb over the city of Nagasaki, Japan. This was the second bomb used on human populations and, so far, the last.

Rhodes, Richard. The Making of the Atomic Bomb. New York: Simon & Schuster, 1986.
Smyth, Henry De Wolf. Atomic Energy for Military Purposes, 1945. California: Stanford University Press, 1989

Manhattan Project National Historical Park

Last updated: August 3, 2020