UPDATE 3-Los Alamos scurries to protect nuclear lab from fire
* Nuclear weapons lab closes due to fire danger
* Fire has potential to double or triple in size (Updates the number of firefighters, paragraph 12)
By Zelie Pollon
LOS ALAMOS, N.M., June 28 (Reuters) - New Mexico fire managers scrambled on Tuesday to reinforce crews battling a third day against an out-of-control blaze at the edge of one of the top U.S. nuclear weapons production centers.
The fire's leading edge burned to within a few miles of a dump site where some 20,000 barrels of plutonium-contaminated waste, including clothing and equipment, is stored at the Los Alamos National Laboratory, fire officials said.
Officials for the government-run lab said the stored waste is considered low-level radioactive material and remains a safe distance from the fire in an area cleared of trees and other vegetation.
Carl Beard, director of operations for the lab, said there has been no release of radioactive or hazardous materials into the environment and there was no immediate threat to public safety, "even in these extreme conditions."
Established during World War Two as part of the top-secret Manhattan Project to build the first atomic bomb, the lab remains one of the leading nuclear arms manufacturing facilities in the United States.
Authorities have suspended routine removal of the waste drums for shipment to a permanent underground disposal site in southern New Mexico, said Los Alamos County Fire Chief Douglas Tucker.
"Because of the fire, they are not moving any of that. It is safer where it is," he said.
The fire, believed to have been ignited on Sunday by a fallen power line, has consumed nearly 61,000 acres (25,000 hectares) of thick pine woodlands in the Santa Fe National Forest, which surrounds the lab complex and adjacent town of Los Alamos on three sides.
Tucker said he feared the so-called Las Conchas Fire, whipped by high, rapidly shifting winds, could soon double or triple in size. The blaze remained listed as at zero percent containment and burning largely unchecked in its third day.
"I seriously believe it could go to 100,000 acres (40,000 hectares)," Tucker told reporters at a news briefing on Tuesday. "We have fire all around the lab. It's a road away."
A small offshoot of the blaze jumped State Highway 4 onto the lab grounds on Monday, burning about an acre (0.4 hectare) of property before it was extinguished about two hours later.
Between 800 and 1,000 firefighters, backed up by several water-dropping helicopters, were battling the blaze on Tuesday evening.
"We've been putting in orders to get as many firefighters here as we can," fire information officer Vanessa Delgado said. "We're trying to get them in as fast as we can."
Lab officials also called in teams late on Monday to monitor air quality, with high-volume air samplers ready to deploy. Hundreds of National Guard troops have been dispatched to back up law enforcement in the area.
Both the town of Los Alamos, home to about 10,000 residents, and the laboratory, with a work force of about 12,000 people, were evacuated on Monday, and the lab will remain closed at least through Wednesday, officials said.
Situated on a hilltop 35 miles (55 km) northwest of Santa Fe, the lab property covers 23,000 acres (9,300 hectares) and includes about 2,000 buildings, none of which has yet burned.
John Witham, a spokesman for the anti-nuclear group Nuclear Watch New Mexico, said it is the only place in the country that produces plutonium pits that are carried in the core of nuclear bombs.
Three metric tons of highly radioactive weapons-grade plutonium is stored in concrete and steel vaults in the basement floor of a building near the center of the complex, with an air-containment system surrounding it, Witham said.
Lab officials said the storage structures were fire safe.
Nuclear Watch New Mexico said on its website its greatest concern was for the 20,000 55-gallon (200-litre) sealed drums of plutonium-tainted waste stored at one corner of the complex, some stacked in the open on asphalt, some in tents, some buried underground.