Nice to see that the security measures are working:

Security officials at the nation’s largest nuclear power plant detained a contract worker with a small explosive device in the back of his pickup truck Friday, authorities said. Authorities said it didn’t appear to be an act of terrorism.
The worker was stopped and detained at the entrance of the Palo Verde Nuclear Generating Station, about a half mile from the containment domes where the plant’s nuclear material is stored, plant spokesman Jim McDonald said. Security officials then put the nuclear station on lockdown, prohibiting anyone from entering or leaving the facility.
Authorities described the device as a small capped pipe that contained suspicious residue.
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Workers must pass through two security checkpoints to get inside one of the plant’s three containment domes, which house the radioactive material. One of the checkpoints includes an automated system that examines workers for the presence of bomb-making materials, McDonald said.
Palo Verde is the nation’s largest nuclear power plant both in size and capacity. Located in Wintersburg about 50 miles west of downtown Phoenix, the plant supplies electricity to about 4 million customers in Arizona, New Mexico, Texas and California.