PHOENIX The Palo Verde nuclear power plant, the largest in the United States, was sealed off for much of Friday after guards found a pipe bomb in a worker's truck as he tried to enter the facility, officials said.
The lock-down of the plant, about 50 miles (80 km) west of Phoenix, Arizona, was lifted on Friday afternoon. Operations were not affected, said the plant's operator, Arizona Public Service.
The driver of the truck, an engineer who had worked at Palo Verde as a contractor for a year, was detained as his apartment was searched but he was not under arrest and was cooperating with authorities, the Maricopa County Sheriff's Office said.
"Our examination and preliminary testing shows it is a viable improvised explosive device," said Capt. Paul Chagolla.
The pipe bomb was probably powerful enough to damage the vehicle but not the power plant, Sheriff Joe Arpaio said.
The engineer, identified as Roger Hurd, 61, of South Carolina, told investigators he was unaware the pipe bomb was in the bed of his pickup truck, the sheriff said.
"The mystery is how did it get in the truck and how he knew nothing about it. It's all very puzzling," Arpaio told Reuters, adding that a search of Hurd's Phoenix-area apartment turned up no clues. "There was nothing there that would connect him to the pipe bomb."
With a combined production capacity of about 3,900 megawatts, Palo Verde's three nuclear reactors can make enough electricity to serve 1.5 million to 2 million homes in Arizona, California, New Mexico and Texas.
There was no threat to the plant at any time and the public was not in danger, said Jim McDonald, a spokesman for Arizona Public Service.
Hurd had access to sensitive areas of the plant but McDonald said the engineer mainly worked in the administrative portion of the facility. The last time he worked in the "protected area" was on Oct. 17.
People and vehicles entering the plant undergo an "extensive" inspection, McDonald said.
"It's not an accident they found it," he said. "It's not like an inspection you go through at the airport. The security is highly trained and they are damned good at what they do and they did it today."
The closest homes, built in the past several years, are less than a mile (1.6 km) from the reactors. Palo Verde has been operating for more than two decades.
Two of the reactors were not running on Friday morning. One is being refueled until the second half of December and the second was to return to the power grid shortly, an Arizona Public Service spokeswoman said. The third reactor was operating fully, she said.
Arizona Public Service, a unit of Pinnacle West Capital Corp (PNW.N), owns 29.1 percent of Palo Verde and gets that share of its generation. The other partners are:
-- Salt River Project (17.5 percent);
-- Edison International's (EIX.N) Southern California Edison Co (15.8 percent);
-- El Paso Electric Co (EE.N) (15.8 percent);
-- PNM Resources Inc's (PNM.N) Public Service Co of New Mexico (10.2 percent);
-- Southern California Public Power Authority (5.9 percent);
-- Los Angeles Department of Water & Power (5.7 percent).