Nuclear Warhead 'Pit' Production: Background and Issues for Congress [Updated March 29, 2004] [open pdf - 126KB]
"A 'pit' is the fissile core of a nuclear warhead. In modern warheads, it creates a nuclear explosion that triggers a substantially larger thermonuclear explosion. All pits currently in the U.S. nuclear stockpile were made at the Rocky Flats Plant near Denver, CO, which opened in 1952. The Department of Energy (DOE) halted pit manufacturing operations there in 1989; the United States has been unable to make stockpile-quality pits- and therefore complete nuclear warheads- since then. This report is intended for those interested in the U.S. nuclear weapons program. It will track the pit budget request and program, and will be updated as needed."
CRS Report for Congress, RL31993