...What now for the B83? How many still exist is a federal secret, but not the weapon’s likely fate, which may surprise anyone who assumes that getting rid of a nuclear weapon means that it vanishes from the face of the earth.Typically, nuclear arms retired from the U.S. arsenal are not melted down, pulverized, crushed, buried or otherwise destroyed. Instead, they are painstakingly disassembled, and their parts, including their deadly plutonium cores, are kept in a maze of bunkers and warehouses across the United States.
...The plutonium cores of retired hydrogen bombs are of particular concern, Mr. Alvarez and others say. Roughly the size of a grapefruit, these cores are usually referred to as pits. The United States now has at least 20,000 pits in storage. They’re kept at a sprawling plant in the Texas panhandle known as Pantex.
The Bulletin of Atomic Scientists (unsurprisingly) has some concerns:
Safely ridding the nation of one of the world’s largest excess stockpiles of weapons-grade plutonium will be no minor feat. At issue is the US Energy Department’s 2016 decision to dilute and dispose of, all told, about 48.2 metric tons of plutonium, including 26.2 tons of components, known as “pits,” from several thousand dismantled thermonuclear warheads and 22 metric tons in other forms. These massive quantities of plutonium are destined for the Energy Department’s Waste Isolation Pilot Plant (WIPP), the nation’s only geologic burial site for radiological waste, dug into a deep-underground salt formation near Carlsbad New Mexico.
48.2 metric tons! That's a lot of plutonium.
(The government seems like it takes old plutonium for new nuclear warheads. I imagine there are a great deal of treaties and precedents stopping us from doing something useful with this plutonium, like, I dunno, getting energy from it by turning it into reactor fuel...)