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SASEBO NAVAL BASE, Japan — The USS Houston leaked about two to four times more radioactive water in Sasebo than in two other Japanese ports, the U.S. State Department announced Tuesday.

Still, the radioactivity leaked by the nuclear submarine’s faulty valve in Sasebo, Yokosuka and Okinawa since 2006 was similar to the natural level of radiation in seawater and posed no threat, said the statement posted to the department’s Japan embassy Web site.

The estimated release of radioactivity into the Sasebo port was 13 kilobecquerels. The leak was 6.3 kilobecquerels off of Okinawa and 3.5 kilobecquerels at Yokosuka Naval Base, the State Department said.

One kilobecquerel, a common measure for radioactivity, is equal to the radiation found in about 2.2 pounds of coffee, according to the World Nuclear Association.

"Hypothetically, if an individual drank the entire amount of radioactivity contained in the water that wept from the Houston valve while in these Japanese ports, the radiation exposure dose … would be less than that same person would receive in 10 days from natural background radiation," a State Department said.

The statement was the most comprehensive yet and laid out a time line of the leak incident, which ignited concerns over radioactivity in the Pacific when it was announced last month.

Sasebo’s city government is requesting increased nuclear-vessel oversight by the United States and the Japanese national government following the Houston leak and said this week the national government has promised funding for more monitoring equipment before 2009.

Sasebo leaders have criticized the national government for a delay in notifying the city of the leak.

According to the State Department time line, the U.S. Navy and atomic experts worked for two weeks to identify the magnitude and cause of the leak before announcing it to the Japanese government.

About a gallon of water containing trace levels of radioactivity spilled onto a sailor July 17 while the sub was in dry dock in Hawaii.

The Navy called the Hawaii Department of Health to report the spill and spent a week on engineering and preparation to check the Houston’s closed valves for leaks, the State Department said.

Valve tests confirmed the leak and an examination by the Knolls Atomic Power Laboratory found "very small" leaks had occurred while the sub was in operation.

By July 31, the laboratory and the Pearl Harbor Naval Shipyard determined the Houston had likely leaked radioactive water in Sasebo, Guam and Hawaii during recent visits, according to the State Department, and the Japanese government was notified Aug. 1.

The Navy concluded on Aug. 7 the submarine had been "steadily leaking a small amount of water above the stringent design specification from June 2006 until Houston was placed in dry dock in July 2008," the State Department said.

"This radioactivity was released in liquid water that wept past a shut valve into harbor water," the State Department release said. "The concentration of radioactivity in the liquid, from trace levels of oxidized metals in the water, was so low that it was similar to the concentration of natural radioactivity in seawater."

The U.S. has maintained the submarine leak was minimal and posed no threat to humans or the environment.

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