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News Release

“Background information and Press Release on INES provisional rating on contaminated water leakage from a water tank at Fukushima Daiichi NPS”

August 28, 2013

In November 2012, the Nuclear Regulation Authority (NRA) of Japan designated the Fukushima Daiichi Nuclear Power Station as “Specified Nuclear Power Facility” for the purpose of proceeding with decommissioning work in reducing risk. Responding to the designation, TEPCO submitted an Implementation Plan to the NRA on December 7, 2012. After some amendments of the plan by TEPCO, the NRA approved it on August 14, 2012.

On August 19, 2013, TEPCO submitted the NRA a report on a leakage of contaminated water from a water tank in a controlled area at the Fukushima Daiichi Nuclear Power Station pursuant to the Act on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Nuclear Reactors.

This is an event of leakage that the contaminated water leaked from the tank in which contaminated water retrieved after cooling the damaged Reactor Units 1 – 3 and then removing cesium has been stored.

At the time when an operator reports the NRA on an accident and incident pursuant to the Nuclear Reactors Act, the NRA usually determines and issues INES provisional rating on the accident and incident. In this regard, the Secretariat of NRA rated the event of contaminated water leakage in question as INES provisional rating Level1 on August 19, 2013.

Later, TEPCO submitted the NRA an additional report dated August 20 regarding the event of water leakage. The report says that the amount of leaked water is estimated to be approximately 300m3.

In this context, at the NRA Commission Meeting held on August 21, it was proposed from the Secretariat of NRA that INES provisional rating Level 3 (serious incident) should be rated to this event of contaminated water leakage rather than Level 1, especially taking into account the large amount of contaminated water leakage, the fact that a safety layer was not available for the water tank in question. And it was concluded at the Meeting that the Secretariat of NRA should ask for overviews of the IAEA regarding INES rating. Finally, the Secretariat of NRA re-evaluated the previous INES provisional rating Level1 to Level3 on August 28, 2013.

Please refer to the following Press Release;

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