After World War II ended, Hanford reactors continued to produce plutonium for atomic weapons.  In addition to the B, D, and F Reactors, five more reactors were built next to the Columbia River as the United States and Russia began to stockpile weapons in what was termed the Cold War.  H Reactor began operations in 1949.  DR Reactor and C Reactor went operational in the early 1950’s.  The K-East Reactor and K-West Reactor were running by 1955.  

In 1959, construction began on the ninth Hanford reactor, called the N Reactor.  N was a dual purpose reactor which produced plutonium for atomic weapons as well as steam for generating electricity.  It was the only dual purpose reactor in the United States and was so advanced that President John F. Kennedy came to Hanford in September of 1963 to dedicate the reactor and to start the construction of the electricity generating component of N.  For two years, from 1963 to 1965, all nine reactors were producing plutonium for America’s defense program.

In the mid-1960’s, some of the older reactors were shut down.  By 1970, B, C, D, DR, F, and H Reactors had been deactivated.  The K-East Reactor stopped production in 1970, followed by the K-West Reactor in 1971, leaving only the N Reactor operating on the Site.

The N Reactor continued its mission of producing plutonium and electricity until 1987.  During a routine maintenance shutdown of the reactor in early 1988, the Department of Energy decided to place it in a “standby” status, and it was never re-started.