Potential Release of Radioactivity from the Nuclear-Powered Submarine USS HOUSTON (Notification of the final report provided by the U.S.)

August 29, 2008

Following requests from the Japanese side to the U.S. concerning the potential release of radioactivity from the nuclear-powered submarine USS HOUSTON, Mr. James P. Zumwalt, Deputy Chief of Mission of the Embassy of the United States of America, notified Mr. Shinichi Nishimiya, Director-General of the North American Affairs Bureau, Ministry of Foreign Affairs (MOFA), in the afternoon of August 29 on the investigation into the cause of the event and the measures already taken, as a follow-up of the interim notification on August 7. Mr. Zumwalt also informed that the notification submitted as a final report (information sheet) contained all information that could be provided to the Japanese side at this point, and the U.S. side does not plan to provide further information.
The outline of Mr. Zumwalt’s explanation and the final notification is as follows:

(1) The cause of the potential release of radioactivity was weepage of water past a shut valve. The shut valve was weeping water at a small rate above the stringent design specifications of the U.S. Navy. As a result of review of the highly detailed records of plant conditions dating back to 2004, the Navy determined that it had been weeping from June 2006 until July 2008, and weepage of this kind had not been previously observed for over 50 years.

(2) The concentration of radioactivity released in liquid, from trace levels of oxidized metal in the water (i.e. Cobalt), was so low that it was similar to the concentration of natural radioactivity in seawater. These trace amounts of radioactivity would have no adverse effect on human health, marine life, or the environment. The total amount of radioactivity potentially released from visits to Japanese ports would be less than that received from a routine chest x-ray.

(3) The U.S. Navy is taking actions to ensure that the stringent performance standard for the HOUSTON valve would be met before USS HOUSTON returns to sea.

(4) The U.S. Government reaffirms that it continues to strictly honor all of its previous commitments regarding the safety of U.S. nuclear vessels, which are supported by concrete measures and stringent specifications.

The Government of Japan (GOJ) considers that the present information from the U.S. side reconfirms the safety of the U.S. nuclear-powered vessels, which play an important role for Japan’s peace and stability. The GOJ will continue to expend all possible means to assure their safety.

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