Tokyo Electric Power Co. acknowledged Aug. 21 that water contaminated with radiation that leaked from a storage tank at the Fukushima No. 1 nuclear power plant may have reached the ocean.
As it reels from this latest blow, TEPCO announced moves to deal with what it called a "crisis situation."
The surface of a drainage ditch near the tank where the leak occurred had radiation readings of 6 millisieverts per hour. The ditch is directly connected to the ocean to the south of the No. 4 reactor.
Highly radioactive water was detected about 50 meters east of the tank where the leak was confirmed. The water was about 650 meters from the ocean. The concrete drainage ditch is about 2.2 meters wide and 1.2 meters deep.
Workers who checked the ditch on Aug. 21 noticed a stain that indicated contaminated water may have flowed down the ditch. While the surface of the ditch had radiation readings of 6 millisieverts, the reading at a height of 1 meter was 0.06 millisievert per hour.
The radiation was lower than the water surface of the tank containing the contaminated water. That led TEPCO officials to believe the radiation of the leaked water may have become diluted after mixing with rain.
TEPCO officials had said previously that no water from the leaking tank appeared to have reached the ocean. Sandbags had been placed around the leaking tank to prevent contaminated water from spreading.
A working group of the Nuclear Regulation Authority held a meeting on the evening of Aug. 21 to discuss the new crisis. An NRA official suggested the leak in the tank was coming from a crack on the bottom.
Although there had been suspicions that water had leaked from the connected areas held together by bolts, there are no signs such a leak occurred.
The NRA group instructed TEPCO to determine the cause of the leak without delay.
The remaining water in the tank that leaked was moved to another tank around 9 p.m. on Aug. 21. TEPCO is frantically trying to determine precisely where the leak took place as well as its cause.
It pledged to make greater efforts to monitor other tanks for possible leaks.
At an Aug. 21 news conference, Zengo Aizawa, TEPCO executive vice president in charge of the nuclear power division, apologized for the latest tank leak and said, "The problem of contaminated water is the largest crisis facing management and we will place priority on dealing with the issue."
He said he would remain full-time at the Fukushima plant site to take charge of the problem.
TEPCO announced measures to collect dirt contaminated by the water as well as to improve the monitoring of the tanks. The company also indicated it would review the organization now set up to deal with decommissioning reactors and handling the contaminated water.
There are about 350 storage tanks similar in structure to the one that leaked. Most do not have meters to measure water levels inside.
Doubts about the reliability of those tanks were also raised because inspections for leaking before the tanks were used were conducted in the rain.
TEPCO officials have said they will inspect all of the tanks.
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