A fisherman makes his way up the Tennessee River past the cooling towers of the Tennessee Valley Authority's Watts Bar Nuclear Plant in Spring City, Tenn.

Mystery still surrounds a TVA security officer's report of a gunfight with an intruder in the middle of the night near Watts Bar Nuclear Plant.

Authorities continue to investigate, and the FBI's Ed Galloway, head of this region's investigative office, has declined to talk about the findings so far.

"We are conducting a logical investigation and pursuing all leads," he said, adding that anyone with information should contact the FBI.

Nuclear Regulatory Commission records show that shootings at the nation's nuclear power plants are rare. Only a couple of others have been reported -- one in 1998, and another 10 years earlier.

Both involved reports of security officers being fired on, and both turned out to be false reports. In each case the security officers had fired a shot while fooling around and then made up the stories of intruders to cover their misfires.

No one is suggesting that's what happened at 2 a.m. Sunday, when the security officer said an intruder exchanged gunfire with him on Watts Bar property near the bank of the Tennessee River at the plant 48 miles northeast of Chattanooga.

TVA spokesman Jim Hopson said the FBI has become the lead agency in the investigation, but the NRC has two investigators who also are reviewing TVA security systems.

It is still unclear why the intruder -- who escaped -- was there, and the nuclear plant remains under high security alert, Hopson said.

David Lochbaum, an independent nuclear power expert who directs the Union of Concerned Scientists' Nuclear Safety Project, is taking a wait-and-see approach to the reports from Watts Bar.

"I'm not saying that this event at Watts Bar is a fabrication -- just that it is possible," Lochbaum said. "Having worked many midnight shifts at nuclear plants, 2 a.m. is a very boring moment."

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In 1998, an armed security guard patrolling the outskirts of Zion Nuclear Plant in Illinois said he saw a person lying near a road. He said he was shot, and he fired six shots at the intruder.

"Security officers from the plant and five units from the Zion Police Department responded. The site security force went into a heightened state of security at the plant. A canine unit from the Lake County Sheriff's Department also assisted. No intruder was found," the NRC record states.

Zion's owner, Commonwealth Edison Co., later reported that the security guard admitted to Zion police "that he had shot himself in the foot, fired the remaining five rounds from his weapon, and fabricated the story about the intruder. There was no intruder. The police arrested the security guard and charged him with disorderly conduct," according to NRC records.

Ten years earlier, at Turkey Point Nuclear Plant in Homestead, Fla., a security guard told police he encountered three unknown people in a picnic area outside the protected area of the plant grounds and one of them made racial remarks to him and pushed him.

The officer said he became frightened and drew his sidearm, accidentally discharging it. The guard told police the discharged round struck the company pickup truck he was driving. The three men reportedly ran into the water and fled in two boats. The guard fired five more shots, some of which hit the truck.

Later he told police that he realized he had not acted in accordance with company policy and decided to invent the armed intruder story. He reloaded his revolver, broke out the driver's-side window on the truck, fired six rounds into the woods and returned to the plant, reporting that he had been fired on.

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When bullets went flying near another TVA facility recently, investigators found a plausible explanation for the gunfire.

A Tennessee Wildlife Resources Agency officer was called a few weeks ago when bullets whizzed near the head of a TVA officer at the guardhouse of the Raccoon Mountain Pumped Storage Plant.

TWRA spokesman Dan Hicks said the TWRA officer and a TVA inspector found a makeshift target range just across the Tennessee River on the property of Prentice Cooper State Forest.

"They saw where there were some tin cans set up on the bank and they thought they were shooting for target practice," Hicks said. "They [the officers] didn't think there was anything other than carelessness involved."

Hicks said TWRA put up temporary signs forbidding shooting there, and resource officers will post permanent signs there this week.

Meanwhile, TVA and NRC officials said searches of the Watts Bar plant, the river pump stations and the riverbanks have turned up no threats. Hopson said there was no threat to public safety during Sunday's incident. The gunshots were fired about 200 yards away from the plant's protected area, he said.

Lochbaum talked about what can happen when boredom and human ingenuity collide.

"With little to do, it's easy for boredom to take over and fill the slow times with things to do," said Lochbaum. "Practicing one's quick draw seems to be among the things that security officers do in times of boredom. And apparently, sometimes the imaginary opponent wins."

Contact staff writer Pam Sohn at psohn@timesfreepress.com or 423-757-6346.