By Laura Zuckerman
SALMON, Idaho (Reuters) - An evacuation order was lifted on Friday for hundreds of workers at a U.S. Energy Department nuclear site in Idaho as firefighters gained ground against a brush fire that has scorched 36,000 acres inside the sprawling compound.
The blaze at the Idaho National Laboratory, an 890-square-mile complex with three active reactors in the high desert of eastern Idaho, presents "no known radiological hazard to the public at this time," lab officials said in a statement.
As the fire grew in size and intensity, the lab on Thursday evening had ordered nonessential personnel to leave a key facility called the Materials and Fuels Complex, where spent nuclear fuel and radioactive wastes are processed. The facility normally is staffed by about 800 workers during the day.
At the same time, workers at another lab installation, the Idaho Nuclear Technology and Engineering Center -- where spent radioactive fuel rods are cooled in storage ponds -- were told to take shelter inside that facility because of heavy smoke, said lab spokeswoman Misty Benjamin.
The evacuation and sheltering orders were lifted Friday morning, and lab officials said some 70 firefighters backed by bulldozers and water-dropping aircraft had managed to carve containment lines around 50 percent of the fire's perimeter.
No special precautions were known to have been taken so far in surrounding populated areas, including Idaho Falls, a city of roughly 57,000 people about 15 miles east of the lab.
The cause of the fire is under investigation.
It is the second of two blazes that have broken out in the parched sagebrush and grasslands surrounding lab facilities this week amid soaring temperatures, gusting winds and lightning strikes.
Crews on Monday contained a blaze that burned more than 100 acres on the northwest edge of the site. Fire managers said that fire was sparked by a vehicle with a blown tire dragging its metal rim along the pavement of a state highway.
The blaze, which blackened about 28,000 acres of lab property on Thursday, had grown to 36,000 acres as of midday Friday, lab officials said.
Some 6,000 employees and contractors work at the Idaho National Laboratory, the Energy Department's lead facility for nuclear reactor technology.
The installation last year grappled with the largest fire in its history, a conflagration that charred 109,000 acres. That fire brought down power lines at the Materials and Fuels Complex, causing officials to rely on backup generators.
Two large-scale fires at the facility within one year sparked alarm among activists with the Snake River Alliance, Idaho's nuclear watchdog group.
"These fires underscore how the nuclear industry and practices at Department of Energy sites pose threats because of unexpected events like floods, fires, earthquakes or other natural disasters," said Liz Woodruff, executive director of the Snake River Alliance.
Fires have charred tens of thousands of acres across Idaho and the Northern Rockies in recent days, including parts of Montana, Yellowstone National Park and northwestern Wyoming.
(Editing by Steve Gorman and Jerry Norton)