The first detonator, known as a "pit," was completed last month and shipped to Texas, but on Monday, the laboratory hosted a ceremonial stamping of approval of a second pit for dignitaries, including U.S. Sen. Pete Domenici, R-N.M., The Albuquerque (N.M.) Journal reported.
The devices are designed for W88 warheads used on nuclear submarines and the lab intends to produce 10 of them a year to replace older ones in rotation, lab Director Michael Anastasio told the Journal.
The United States hasn't produced nuclear warheads since 1989 when a facility in Rocky Flats outside Denver was closed due to environmental problems.
As the ceremony concluded, the Physicians for Social Responsibility group had a news conference at a Los Alamos hotel denouncing the resumption.
"Nuclear weapons development is just not needed," spokesman Mike McCally said in the Journal report. "We rather should be moving toward reducing our weapons stockpile."