Tepco Says Contaminated Water Tank Leak May Have Started in July

The leak at a contaminated water storage tank discovered last week at the Fukushima plant may have continued since last month before it was detected and the tank drained, plant operator Tokyo Electric Power Co. (9501) said.

Crews found elevated levels of radiation in July near where the leak was ultimately detected on Aug. 19, Mayumi Yoshida, a spokeswoman for the utility known as Tepco, said today by phone.

Tepco originally characterized the leak as a small one before determining by the change in the tank’s water level that 300 metric tons of contaminated water had escaped. A protective barrier around the tank didn’t stop the leak because a valve in the concrete structure had been left open, Tepco said.

Japan’s Nuclear Regulation Authority last week labeled the leak a “serious incident” in its worst assessment of the problems at Fukushima since the earthquake and tsunami of 2011 caused reactors to melt down.

To contact the reporter on this story: Jacob Adelman in Tokyo at jadelman1@bloomberg.net

To contact the editor responsible for this story: Jason Rogers at jrogers73@bloomberg.net

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