Sitting squarely in the middle of the now decommissioned Hanford Site, a nuclear production complex on the Columbia River near Richland, Washington, is B Reactor—the world’s first large-scale nuclear reactor ever built. For more than forty years, B Reactor, along with eight others, pumped out enough plutonium to build over sixty thousand nuclear weapons that comprises the majority of America’s vast nuclear arsenal. B Reactor is one of the few facilities constructed during the secretive Manhattan Project that’s still standing and accessible to the public.

The front face of the reactor core. Image credit: Jeff Keyzer/Flickr