A former engineer at the nation's largest nuclear power plant has been charged with taking computer access codes and software to Iran and using it to download details of plant control rooms and reactors, authorities said.

The FBI said there's no indication the plant employee training software had any terrorist connections.

Mohammad Alavi, who worked at the triple-reactor Palo Verde power plant west of Phoenix, was arrested April 9 at Los Angeles International Airport when he arrived on a flight from Iran, authorities said.

Alavi, 49, is a U.S. citizen and denies any wrongdoing, said his attorney, Milagros Cisneros of the Federal Defender's Office in Phoenix.

He is charged with a single count of violating a trade embargo that prohibits Americans from exporting goods and services to Iran. If convicted, he would face up to 21 months in prison.

According to court records, the software is used only for training plant employees, but allowed users access to details on the Palo Verde control rooms and the plant layout. In October, authorities alleged, the software was used to download training materials from Tehran, using a Palo Verde user identification.

The FBI said there was no evidence to suggest the software access was linked to the Iranian government, which has clashed with the West over attempts to develop its own nuclear program.

"The investigation has not led us to believe this information was taken for the purpose of being used by a foreign government or terrorists to attack us," said Deborah McCarley, a spokeswoman for the FBI in Phoenix.

Officials of Arizona Public Service Co., the Phoenix-based utility company that operates the Palo Verde Nuclear Generation Station, said the software does not pose a security risk because it doesn't control any of the nuclear plant's operating systems.

However, the utility said it has changed software security procedures since Alavi quit in August after working there for 16 years.

Palo Verde has been plagued by outages and equipment problems for the past several years.

The plant, located about 50 miles west of downtown Phoenix, supplies electricity to some 4 million customers in Arizona, New Mexico, Texas and California.