Stars and Stripes reported the USS Ronald Reagan Carrier Strike Group moved its ships and aircraft away from the Fukushima nuclear plant, where the Japanese are struggling to avert a meltdown after Friday's mammoth earthquake and tsunami.
Low levels of contamination were found in the air and on the crews of three helicopters returning from relief work near Sendai.
The 17 crew members were easily cleaned by washing, and the move is only temporary, the Navy said. It said their exposure was less than a month's worth of background radiation.
The Reagan strike group was heading to South Korea for joint military exercises when it was diverted to Japan. It arrived Sunday to support disaster aid in devastated Miyagi and Fukushima prefectures.
"They received very, very low levels of contamination," Cmdr. Jeff A. Davis told The Washington Post by telephone.
"It certainly is not cause for alarm. It is something we have to watch very carefully and make sure we are able to monitor, and to mitigate against this environmental hazard."
The aircraft carrier and other U.S. warships in the region will not be in the path of wind-carried radiation, the Post said.
Word of the contamination experienced by U.S. personnel came as Japan braced for possible nuclear disaster Monday as officials desperately worked to prevent multiple reactor meltdowns after the earthquake and tsunami.
The disaster left more than 3,500 people confirmed dead, thousands more unaccounted for, more than 300,000 homeless, and millions without water, power, heat or transportation. The country's prime minister called the calamity the country's worst crisis since World War II.
Explosions have occurred at two of six boiling-water reactors at the Fukushima Daiichi nuclear power plant in the 11,000-person town of Okuma in Fukushima prefecture's Futaba district, with the second explosion occurring Monday.
The latest explosion did not appear to have harmed the reactor, but at least six people were injured in the blast, Japanese officials said.
Workers flooded the two stricken reactors with seawater and then released steam, officials said, to avoid a full nuclear meltdown.