Tokyo Electric Power Co. has disclosed yet another case of radioactive water leaking from an aboveground steel storage tank at the stricken Fukushima No. 1 nuclear power plant.
It said a worker spotted water leaking at a rate of one drip per 3-4 seconds shortly after midday on June 5.
The contents were quickly moved to a nearby empty tank, one of
dozens that are being used for contaminated water transferred from underground reservoirs.
The immediate concern was whether there was a structural failure in the tank and that similar incidents could occur.
The worker patrolling the area detected the leak from a joint about 4 meters from the bottom on the side wall of a 10-meter-high tank around 12:15 p.m.
The worker tried to stop the leak by tightening bolts that hold the tank together. When that failed, water was transferred to an empty tank nearby until the water level was lower than the joint.
The leak stopped after about 4 hours. The spillage amounted to less than 1 liter, which TEPCO said would have minimal impact on the environment.
The above-ground storage tank can hold 500 tons of water.
The discovery of leaks of contaminated water from underground storage tanks in April prompted TEPCO to move quickly to build new aboveground storage tanks. Thirty-eight cylindrical tanks, made of steel plates joined together by bolts, were newly installed in May.
This process allows the tanks to be built more quickly than when welding is involved. There have been three similar leaks involving the same type of steel tanks in the past, a TEPCO official said.
The plant complex has 63 such tanks, the official said.
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