U.S. submarine radiation leak sparks concern in Japan

TOKYO (Reuters) - A small amount of radiation leaked from a U.S. nuclear-powered submarine that stopped by Japan earlier this year, the Japanese government said on Saturday, prompting calls by civic groups for full disclosure.

The leak, which was too small to have any impact on the environment, was found during an inspection of the nuclear-powered Houston in Hawaii, the Japanese Foreign Ministry said, citing information provided by the U.S. government on Friday.

"The amounts were very, very, very small and were not of the sort that would affect the human body or the environment," Chief Cabinet Secretary Nobutaka Machimura told a news conference.

The incident comes at a time when the United States has been trying to allay fears over the planned stationing of nuclear-powered aircraft carrier George Washington in Japan, the only country to have suffered nuclear attacks.

The foreign ministry said some cooling water was found seeping out from the submarine, which had stopped over in Japan in March and April, adding that it was unclear when such seepage had first occurred.

Twenty-four hour radiation monitoring conducted by the government during the Houston's stay in Japan in March and April had revealed no irregularities, the Foreign Ministry said.

Since March, the Houston was deployed in the Pacific Ocean, a foreign ministry official said.

Over the course of that deployment, the total amount of radiation that could have leaked from the Houston was roughly equivalent to the amount that can be found in a bag of fertiliser, the ministry said.

Many Japanese are sensitive about the use of nuclear power by military forces. The Japanese cities of Hiroshima and Nagasaki came under nuclear attack from the United States at the end of World War Two in August 1945.