The U.S. government Friday filed its final report on the submarine USS Houston’s radioactive leak earlier this year, saying it had no adverse effect on human health or the environment, the Foreign Ministry said.
The incident came to light on Aug. 1 when the United States notified Japan that the Los Angeles-class fast-attack sub may have leaked radioactive water during port calls at Nagasaki, Kanagawa and Okinawa prefectures.
Friday’s report submitted by the U.S. Embassy’s deputy chief of mission, James Zumwalt, concluded that the leak of a total potential amount of 0.605 microcuries was due to water seeping out of a shut valve.
Similar leaks out of valves “have not been previously observed,” the report said, but it assured that the U.S. Navy will take action to ensure the safety of the valve before the Houston sails again.
“The navy’s periodic valve testing, rigorous performance standards” and practice of addressing minute anomalies is effective in protecting the public and the environment, the report said.
“Hypothetically, if an individual drank the entire amount of radioactivity contained in the water that leaked from the Houston’s valve while in Japanese ports, the radiation exposure to the individual would be less than that same person would receive in 10 days from natural background radiation,” it said.
The report stated that extensive monitoring by the U.S. Navy has confirmed that no discernible effect to the environment has been made by a U.S. nuclear sub since checks began in the 1960s.
According to the report, the USS Houston had been steadily leaking small amounts of radioactive water since June 2006.
The glitch was found when the sub was in dry dock at Pearl Harbor for maintenance on July 17.
During this period it made 11 port calls in Japan, beginning in July 2006 and most recently in April. The sub leaked a cumulative 0.34 microcuries of radioactivity in Sasebo, Nagasaki Prefecture, 0.095 microcuries in Yokosuka, Kanagawa Prefecture, and 0.170 microcuries at a U.S. base in Uruma, Okinawa Prefecture.
The Foreign Ministry released a statement that the report “reassured the safety of U.S. nuclear submarines and the vital role they play in securing peace and stability for our country.”
The Foreign Ministry, which came under criticism for not immediately releasing the initial U.S. disclosure of the leak earlier this month, has said no abnormalities were recorded at the three ports during the sub’s visits.