TOKYO — A U.S. Navy submarine leaked trace amounts of radiation during a two-year span while in ports in Japan and Guam, officials from both governments said Thursday after receiving military briefings.

The leak began in June 2006 and lasted while the USS Houston visited ports in Sasebo, Okinawa and Yokosuka, Japan, and in Apra Harbor in Guam, according to Japan’s Ministry of Foreign Affairs and the governor’s office of Guam.

The amount, according to a ministry report released Thursday afternoon, was so small "that it was below the limit of detection by personnel on the ship and was indistinguishable by the ship from no leakage at all."

Still, the acting governor of Guam, Michael W. Cruz, called Thursday for independent testing of the waters in and around Guam’s port area. The Houston, a fast-attack Los Angeles-class attack submarine, is based in Guam.

"We are concerned about this new information and we will do everything we can to ensure the safety and well-being of our people," Cruz said in a written statement.

A U.S. Embassy spokesman confirmed Thursday afternoon that James Zumwalt, the embassy’s second-in-command, met with Japan ministry officials to update them on the Navy’s investigation.

The Navy discovered the leak July 17 while the Houston was in drydock in Pearl Harbor, Hawaii, for routine maintenance, Navy officials have said. About a gallon of water spilled onto a sailor when a fitting came loose, and that water tested positive for radiation.

A week later, tests showed a valve was leaking at a small rate, the ministry wrote in its report, which is a summary of the Navy’s findings, a spokesman at Yokosuka Naval Base said Thursday evening.

The water that spilled in July on the sailor contained about half a microcurie of radiation, or about half as much as in a 50-pound bag of commercial fertilizer, Navy officials said last weekend.

"This (leak) was minuscule and below normally datable amounts," Yokosuka spokesman Cmdr. Ron Steiner said Thursday. He said the Navy’s willingness to talk about such a trace amount showed its commitment to safety and openness with Japan.

On Saturday, a representative of a Yokosuka protest group called the leak on the Houston a "grave concern."

"The radiation leakage (of the) USS Houston and a fire aboard the USS George Washington completely wiped out the Navy’s assertion that U.S. Navy nuclear-powered vessels are safe and produce no radiation leakage," Masahiko Goto wrote in a statement on Saturday.

The USS Kitty Hawk, the Navy’s last conventionally powered carrier, left its home in Yokosuka May 28. It is due in San Diego to begin swapping crews with the George Washington on Friday, officials said.

A summary of the Navy’s findings is available in English at the ministry’s Web site at

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Hana Kusumoto is a reporter/translator who has been covering local authorities in Japan since 2002. She was born in Nagoya, Japan, and lived in Australia and Illinois growing up. She holds a journalism degree from Boston University and previously worked for the Christian Science Monitor’s Tokyo bureau.

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