Workers at Hanford and other sensitive sites in the region are to report to work this morning, but will find increased security measures following Tuesday's terrorist attacks.

Almost 6,000 Hanford employees were sent home Tuesday morning after the attacks on the Pentagon and World Trade Center towers -- leaving just skeleton crews on the nuclear reservation.

Those same evacuations emptied the Federal Building in Richland and the Hanford contractors' headquarters buildings at Stevens Center in north Richland.

Hanford's federal and contractor employees should report to work today, starting with the day shift, said Manny Van Pelt, a Department of Energy spokesman.

Similar actions are being taken at other DOE sites across the nation.

"The heightened security will remain in effect, so employees should expect delays (entering the site and their buildings)," Van Pelt said.

Extra security measures will remain today at Energy Northwest's nuclear reactor at Hanford and Framatome ANP's nuclear fuel fabrication plant in Richland.

The Energy Northwest plant was put on the second-highest level of alert Tuesday shortly after the bombings. A short time later, the Nuclear Regulatory Commission recommended that level of security for all of the nation's nuclear reactors.

And in Hermiston, security was quickly tightened at the Umatilla Chemical Depot, where tons of deadly nerve gas are stored.

The Corps of Engineers also upgraded security and closed McNary and other dams to visitors and canceled tours on the Columbia and Snake rivers. Employees were allowed access and business continued at district headquarters in Walla Walla.

A spokeswoman said the agency could not discuss the "heightened" security measures.

The Bonneville Power Administration evacuated nonessential employees from its federal facilities and canceled planned maintenance outages on its regional power transmission system to maintain flexibility.

In Richland, armed guards and bomb-sniffing dogs were stationed at the Federal Building -- which usually has a couple on duty -- and at the Stevens Center. Also, U.S. District Court in the Federal Building was closed Tuesday, but will reopen today.

Parked vehicles were removed Tuesday from parking spots closest to the Richland buildings, and those areas were blocked off with orange cones or yellow tape. Those measures will continue today, Van Pelt said.

At courthouses in Benton and Franklin counties and around the Mid-Columbia, security personnel have been put on alert and extra personnel have been added.

DOE also increased security at the checkpoints on roads leading into Hanford.

Normally, guards at the checkpoints only look at the security badge of a vehicle's driver, assuming that individual is responsible for everyone else in the vehicle.

But now the badge of each person entering Hanford or a north Richland Hanford building is being checked closely, and will be until further notice, Van Pelt said.

Energy Northwest boosted security patrols inside and outside of its security fence, said spokesman Don McManman. But both Energy Northwest and Framatome are continuing full operations.

Energy Northwest's reactor is inside a containment chamber with concrete walls that are several feet thick and reinforced by metal rebar the diameter of a human wrist, McManman said.

The reactor building itself was built strong enough to withstand a direct hit from a Boeing 747.

In case of a disaster, the reactor would automatically shut down. And valves would automatically shut off any potentially contaminated steam that could escape through the cooling towers, McManman said.

All environmental cleanup work and other nonessential activities were stopped Tuesday at Hanford after managers became worried about safety issues because of workers being distracted by the news of the terrorist attacks, Van Pelt said. That could increase safety risks, he said.

The PFP, which holds 4.4 tons of plutonium mixed within 19.6 tons of scrap, has been universally considered the prime target at Hanford for any terrorist strike.

Most of the scrap plutonium is in a huge vault, but a couple hundred pounds of plutonium dust and residue is believed to be scattered in the PFP's ducts. The PFP building has concrete walls that are several feet thick, though a chemical tank explosion in 1997 did punch a hole through the roof.

At the Umatilla Chemical Depot in Hermiston, Depot Commander Lt. Col. Fred Pellissier first heard of the tragedy from television news reports at his home. He later was contacted by his headquarters at the U.S. Army Soldier and Biological Command at Aberdeen Proving Ground in Maryland, said depot spokeswoman Mary Binder.

Some depot operations are continuing, but with a high level of security in effect. "Only essential personnel are being allowed on base," Binder said.

Work is continuing at the nerve gas incinerator plant, where about 450 employees are testing the newly built facility, said Loren Sharp, project manager for Washington Demilitarization Co.

Security at the plant is being provided by Army personnel from the Umatilla Chemical Depot, he added.

Pellissier was quick to call Hermiston Mayor Bob Severson after the attacks to let him know security would be tighter at the depot, where 12 percent of the nation's stockpile of chemical weapons are stored, waiting for incineration.

"This is why the nerve gas out there needs to be destroyed," Severson said. "As long as it is there, there is a risk factor. Nobody knows where this is going or where the next attack will be."

Other potentially vulnerable spots at Hanford could include:

n The underground radioactive waste tanks in the site's center, 15 to 17 miles from Richland. These tanks are beneath at least 6 feet of soil.

n The K Basins, which hold 2,300 tons of spent nuclear fuel stored in two water-filled, leak-prone indoor pools about 400 yards from the Columbia River. The K Basins are about 30 miles from Richland.

n About 1,500 barrels of uranium chips stored in oil just north of the 300 Area, about three miles north of Richland. Most of the barrels are buried, but 200 to 300 have been unearthed.