From http://www.dnfsb.gov/index.php:
The Defense Nuclear Facilities Safety Board is an independent federal agency established by Congress in 1988. The Board's mandate under the atomic Energy act is to provide safety oversight of the nuclear weapons complex operated by the Department of Energy (DOE). The nuclear weapons program remains a complex and hazardous operation. DOE must maintain readiness of the nuclear arsenal, dismantle surplus weapons, dispose of excess radioactive materials, clean up surplus facilities, and construct new facilities for many purposes. The constant vigilance of the Board is required to ensure that all of these activities are carried out by DOE in a manner that provides adequate protection for the public, workers, and the environment.