The head of the agency responsible for the U.S. nuclear weapons stockpile said on Friday that he will leave his post in January, Reuters reported, six months after three elderly peace activists broke into the government’s maximum-security facility for weapons-grade uranium. The departure of Thomas D’Agostino, the administrator at the National Nuclear Security Administration (NNSA), has nothing to do with the security breach, an NNSA official said. D’Agostino, who worked for the government for more than 36 years and had been head of the NNSA for more than five years, had been asked to stay in the job but declined, the official said.