By Laura Zuckerman
SALMON, Idaho (Reuters) - Firefighters struggled on Thursday to control a fast-growing 28,000-acre wildfire raging within several miles of spent nuclear fuel stored at a U.S. Energy Department lab in the high desert of eastern Idaho.
The growth and intensity of the blaze, the nation's largest active wildfire, prompted the Idaho National Laboratory to order a key facility on the 890-square-mile site evacuated of all nonessential personnel, lab officials said.
The Materials and Fuels Complex, about 38 miles from Idaho Falls, consists of facilities for handling, processing and examining spent nuclear fuel, irradiated materials and radioactive wastes, according to the lab's website.
Technicians perform this work with remotely operated tools and equipment placed inside shielded chambers to contain contamination and radiation.
Fire crews were taking preventive measures to safeguard the facility's buildings, which are also surrounded by buffer zones of gravel or sand, lab spokesman Ethan Huffman said.
A statement issued late Thursday by the lab, which employs roughly 6,000 people, including contractors, added: "There is no known radiological hazard to the public at this time."
Earlier in the day, nearly 50 firefighters from the lab and the U.S. Bureau of Land Management focused their efforts on protecting a separate facility where spent nuclear rods are stored, according to the lab.
Additional radioactive rods are kept cooled in storage ponds farther to the south at a site called the Idaho Nuclear Technology and Engineering Center.
The center's workers "have taken shelter at the facility as a precaution," the lab said in a late update without further explanation.
"They're fighting (the fire) from all directions at the moment; winds are changing every minute," lab spokeswoman Sara Prentice said Thursday afternoon.
The exact distance between the leading edge of the rapidly spreading blaze and various facilities on the laboratory grounds, which also includes three working reactors, was not precisely known Thursday night, lab officials said.
But flames did reach to within several miles of sites where spent nuclear fuel is kept, including the Materials and Fuels Complex and the so-called Naval Reactors Facility.
CAUSE UNDER INVESTIGATION
Thursday's blaze at the lab came three days after crews extinguished an earlier fire that burned through sagebrush and grasslands on the northwest edge of property.
Government officials said that blaze was sparked by a vehicle with a blown tire dragging its metal rim along the pavement of a state highway near the laboratory.
The cause of the new blaze was under investigation. It is one of five wildfires that erupted in eastern Idaho on Thursday amid lightning strikes, high temperatures and strong winds.
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.
The National Weather Service on Thursday heightened fire warnings for the region because of soaring temperatures, dwindling humidity and predicted lightning storms with wind gusts of up to 35 miles per hour.
Hot, dry, windy conditions also posed difficulties on Thursday for the 170 firefighters assigned to a separate fire blazing out of control in forested high country of east-central Idaho and western Montana.
The Saddle Complex blaze, which has scorched 21,100 acres in Idaho's Salmon-Challis National Forest and the Bitterroot National Forest of Montana, was burning with such intensity and in such rugged terrain that fire bosses deemed it unsafe to launch an attack except by air.
"These aren't the kind of conditions you put people in," U.S. Forest Service spokesman Bob MacGregor said.
Ground crews on Thursday worked to protect 30 outlying homes and establish perimeters in advance of oncoming flames.
Authorities in Montana told residents of 50 houses west of Darby to prepare for evacuation, and smoke in the Bitterroot Valley prompted health officials to advise small children and people with respiratory or heart problems to stay indoors.
(Editing by Steve Gorman, Jerry Norton and Cynthia Johnston)