The United States has an arsenal of some 3,800 nuclear weapons, about half of which are deployed, with the rest in storage. The Department of Energy’s National Nuclear Security Agency (NNSA) and the nuclear weapons laboratories it oversees are concerned that the performance of the weapons will degrade over time. Most of the components can be—and are being—replaced with new versions, so the main concern is the behavior of aging plutonium “pits” at the core of all U.S. weapons.
