More leaks found at Fukushima nuclear plant

FILE - This Aug. 20, 2013 aerial file photo shows the Fukushima Dai-ichi nuclear plant at Okuma in Fukushima prefecture, northern Japan. Japan's nuclear regulator has upgraded the rating of a leak of radiation-contaminated water at its tsunami-wrecked nuclear plant to a "serious incident" on an international scale. (AP Photo/Kyodo News, File)

Japan's top nuclear regulator raised safety concerns Monday about hastily built storage tanks and their foundations amid signs of more leaks of radiation-contaminated water.

Nuclear Regulation Authority Chairman Shunichi Tanaka said that a small leak and signs of possible leaks have been spotted at several other Fukushima Dai-ichi storage tanks since a major leak in August that added to concerns about the plant's stability.

The plant's operator, Tokyo Electric Power Co., reported a loss of 300 tons of radiation-contaminated water from a steel tank on Aug. 19, saying most of it is believed to have seeped underground but some might have escaped into the sea. The company has yet to determine the cause or exactly where the water went.

The massive leak of water used to cool the plant's three melted reactor cores triggered fears of similar leaks from more than 300 other similar tanks. The tanks are part of approximately 1,000 tanks holding 330,000 tons of contaminated water at the plant, where the radioactive waste water from the reactors grows by 400 tons daily.

The latest leaks have triggered further concerns about the plant's ability to manage the contaminated water. Experts have said that radiation-contaminated water leaking from underground and utility tunnels connected to reactors and turbine buildings has been leaking into the sea for some time.

Tanaka said he believed the discoveries of the subsequent leak and signs of possible leaks were the result of closer inspections after leak two weeks ago. That leak was the worst from a tank at the plant, where three reactors melted down following the March 2011 earthquake and tsunami.

Tanaka raised concerns about the safety of the foundations of the tank sites. TEPCO recently revealed that one of the tank sites had partially sunk during a test to see if the tank was watertight.

"Because those tanks were built in an emergency situation, it is questionable whether sufficient ground surveys were conducted," Tanaka said. "We believe experienced companies did a fine job, but we still have concerns and we must step up our watch for leaks."

The plant's operator says the latest small leak was found over the weekend at a connecting pipe, and added it suspects possible leaks from at least three other tanks where high radioactivity was detected nearby, although it was not considered deadly.