Small amounts of radiation were detected near a U.S. nuclear submarine while it made a port call at Yokosuka, Kanagawa Prefecture, earlier this month, the government said Wednesday.
Tests found radioactive material, including cobalt 60, in the water off Yokosuka port while the USS Honolulu attack submarine was visiting, according to Natsuko Miyakawa of the Education, Culture, Sports, Science and Technology Ministry. The submarine left port Sept. 14.
The radiation was in such small quantities that it posed no danger to people or the environment, Miyakawa said.
A U.S. Navy spokeswoman in Yokosuka, who would not give her name, citing protocol, said she was not aware of the test results.
Japanese officials said the USS Honolulu, based in Pearl Harbor, Hawaii, and other nuclear submarines make frequent stops in Japan.
It was not immediately clear how long the submarine had been in Yokosuka.
The U.S. has about 50,000 service members in bases across Japan under a bilateral security pact. The U.S. plans to deploy the USS George Washington, a Nimitz-class nuclear-powered aircraft carrier, to Japan in 2008.