While not actually part of the Monument, the B Reactor lies just outside its boundaries, and many potential access points lie on or cross the Monument.
Nine reactors eventually were built on the Hanford Nuclear Reservation in response to various world events (e.g., the launching of Sputnik by the Soviet Union). The B Reactor was the first—there was no A Reactor at Hanford—and was built as part of weapons development in World War II and in response to concerns over German development of nuclear capability (later learned to be unfounded).
Built in just 13 months, B Reactor was the first full-scale reactor in the world, producing weapons-grade plutonium. Plutonium from the B Reactor was used in the world’s first nuclear explosion, July 16, 1945, at the Alamogordo Bombing and Gunnery Range in New Mexico.
B Reactor plutonium was used in the "Fat Man" bomb dropped on Nagasaki, Japan, on August 9, 1945. Fat Man, exploding in a 20 kiloton blast, devastated more than two square miles of the city and caused approximately 45,000 immediate deaths and as many as 150,000 total. Japan sued for peace five days later.
As a result of its history and the fact that it was the "first" in many categories, the B Reactor has received many designations. Current designations:
Because of its historical importance and contributions to world events, there is a significant movement to preserve this landmark. The National Park Service has studied the B Reactor and determined that it should be preserved as part of a national historical park. Legislation to create just such a park is working it’s way through Congress.
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Once a national wildlife refuge itself, Saddle Mountain National Wildlife Refuge still exists, but as part of the much larger Hanford Reach National Monument.