The National Nuclear Security Administration NNSA

In 1999 investigators concluded that nuclear secrets had leaked from Los Alamos and that the Energy Department's security was, in the words of one congressional report, a dysfunctional bureaucracy. Congress responded by carving the weapons program out into a semi-autonomous agency within the department. The National Nuclear Security Administration was created by the defense authorization act of October 5, 1999, and began operating in March 2000, with its own Administrator, budget line, and personnel rules, insulated from the rest of the department while remaining under the Secretary.

The NNSA is responsible for the safety, security, and reliability of the American nuclear stockpile of roughly 3,700 warheads. Because the United States has not conducted an explosive nuclear test since 1992, the agency certifies the weapons through stockpile stewardship: supercomputer simulation, experiments at facilities such as the National Ignition Facility, and periodic life-extension programs that refurbish or replace aging components. It is also rebuilding the capacity to manufacture plutonium pits, the cores of warheads, which the country has barely produced since the Rocky Flats plant closed in 1989.

The agency's work is done mostly by contractors at three weapons laboratories, Los Alamos, Lawrence Livermore, and Sandia, and at production sites including the Pantex plant in Texas, the Y-12 complex in Tennessee, the Kansas City campus, the Savannah River Site, and the Nevada National Security Site, where underground tests were once conducted. It also runs the naval reactors program, jointly with the Navy, and nonproliferation programs that secure nuclear materials worldwide. Its budget, about 25 billion dollars, is now larger than the rest of the Energy Department's civilian programs combined.

The agency is in the middle of the most ambitious weapons modernization since the Cold War, replacing or refurbishing nearly every warhead type while building new production plants, and its programs have repeatedly run years late and billions over estimate. Arms control advocates question whether the scale is necessary. Defense planners point to China's rapid expansion of its arsenal and Russia's new delivery systems. The early 2025 mistaken firing of hundreds of NNSA staff, quickly reversed, showed how thin the agency's specialized workforce is.