Emergency officials are holding a preparedness exercise for a mock incident at Palo Verde Nuclear Generating Station west of Phoenix.
The Maricopa County emergency management department says Wednesday's daylong exercise involves more than 400 state, local, and tribal agency staffers. Also involved will be volunteer groups and staff from the nuclear plant operated by Arizona Public Service.
Emergency management spokeswoman Julie Syrmopoulos says the public should not be concerned about numerous emergency vehicles in the area.
The exercise is designed to ensure emergency facilities and a joint information center can activate quickly. Teams that monitor for radiation and another that decides on evacuations or sheltering of nearby residents also are involved.
Federal Emergency Management Agency and the Nuclear Regulatory Commission staff will evaluate the response.