Within every American nuclear weapon sits a bowling-ball-size sphere of the strangest element on the planet. This sphere, called a plutonium pit, is the bomb's central core. It's surrounded by conventional explosives. When those explosives blow, the plutonium is compressed, and its atoms begin to split, releasing radiation and heating the material around it. The reaction ignites the sequence of events that makes nuclear weapons nuclear.
In early nuclear bombs, like the ones the U.S. dropped on Japan in World War II, the fission of plutonium or uranium and the fatal energy released were the end of the story. In modern weapons, plutonium fission ignites a second, more powerful stage in which hydrogen atoms undergo nuclear fusion, releasing even more energy. The U.S. hasn't made these pits in a significant way since the late 1980s.
But that is changing. The country is modernizing its nuclear arsenal, making upgrades to old weapons and building new ones. The effort includes updated missiles, a new weapon design, alterations to existing designs and new pits. To accomplish the last item, the National Nuclear Security Administration has enacted a controversial plan to produce 50 new pits a year at the Savannah River Site in South Carolina and 30 pits a year at Los Alamos National Laboratory in New Mexico, the birthplace of the bomb. The first pits will be designed for a weapon called W87-1, which will tip the new intercontinental ballistic missile, called Sentinel. After that the complex will produce pits for other bomb designs.
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