Los Alamos National Laboratory

The U.S. agency that oversees the nation's nuclear arsenal is moving ahead with plans to modernize production of key components that trigger the weapons. But some watchdog groups and members of Congress are warning of more delays and cost overruns. The National Nuclear Security Administration delivered its annual plan to Congress this week. It outlines the multibillion-dollar effort to manufacture plutonium pits at national laboratories in New Mexico and South Carolina.