The fired workers were among 23 suspended this summer after two computer disks containing classified information went missing. The discovery July 7 prompted a virtual shutdown of the nuclear lab, idling roughly 12,000 workers.
The other 18 workers will retain their jobs but will be reprimanded or demoted from management, Director Pete Nanos told The Associated Press.
"It's very important to get this behind us," Nanos said in an interview via cell phone from an airplane after meetings in Washington, D.C.
Nanos would not discuss the specific cases of fired employees but said that some were dismissed for "not taking actions that you were supposed to take, or signing off on things that you hadn't done." He said one had not taken the appropriate precautions in a safety area.
"We really did fit the punishment to the acts that were done," Nanos said.
Three of the workers were fired in connection with the missing computer disks; the other two were involved in an accident in which a laser injured an intern, he said.
Nanos also said the northern New Mexico lab has finished its investigation into the two missing disks, also known as "classified removable electronic media," or CREM. Information from the probe has been turned over to federal authorities. Nanos refused to release additional details. He said other agencies are still investigating.
Nanos, who held a series of all-hands meetings with lab workers after the scandal broke, added that the "commitment of employees right now is extremely high."
Lab spokesman James Fallin emphasized "that today's announcements provide very clear evidence that it's not business as usual at this laboratory. ... Accountability is the order of the day."