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The Hanford B-Reactor was the first plutonium production reactor to be placed in operation. Its success made possible the subsequent development of atomic energy. The research work, engineering, and planning required to make the reactor operate is one of our most advanced achievements. Much of the reactor core, cooling system, shielding, and auxiliary systems were designed by mechanical engineers.

In the first nine months of operation, the B reactor produced fissionable plutonium for the world's first atomic bomb (the Trinity test on July 16, 1945), and for the atomic bomb that was dropped on Nagasaki, Japan, on August 9, 1945, killing 35,000 people.  This, and similar destruction at Hiroshima caused by the atomic bomb dropped three days earlier, hastened the end of World War II.