Atomic weapons are highly complex, surprisingly sensitive, and often pretty old. With testing banned, countries have to rely on good maintenance and simulations to trust their weapons work.
https://www.wired.com/story/nuclear-weapons-testing/?utm_source=dlvr.it&utm_medium=blogger
https://www.wired.com/story/nuclear-weapons-testing/?utm_source=dlvr.it&utm_medium=blogger