Tokyo Electric Power Co. said it released 1,130 tons of water left behind by powerful Typhoon No. 18 on Sept. 16 onto the soil of the crippled Fukushima No. 1 nuclear power plant after determining contamination levels were below safety standards.
Tokyo Electric Power Co. said it released 1,130 tons of water left behind by powerful Typhoon No. 18 on Sept. 16 onto the soil of the crippled Fukushima No. 1 nuclear power plant after determining contamination levels were below safety standards.
The rainwater collected behind seven concrete barriers, each enclosing a group of storage tanks holding radioactive water on the grounds.
The utility said its workers took the "emergency measure" after confirming that the water in each area contained lower radioactive strontium levels than the legal limit.
TEPCO said it decided to drain the water because if another leak occurred in the storage tanks and went unnoticed, it could contaminate the rainwater accumulated inside the enclosure.
Each concrete barrier in the enclosure is about 30 centimeters high and is equipped with a drainage valve. The valves used to be kept permanently open until the discovery in August that 300 tons of highly radioactive water had leaked from a storage tank in an area called "H4."
TEPCO decided to keep the valves closed after the Nuclear Regulation Authority warned that any leaking water from a tank could flow outside the enclosure if the valves remained open.
The utility said Sept. 17 that the water was drained from seven areas, where rising water levels were flooding the concrete foundations of the storage tanks. It said workers opened valves on the barriers surrounding those areas to drain the water between about 12:40 p.m. and 4:30 p.m. on Sept. 16.
The water, which flowed onto the surrounding soil, may eventually find its way into the nearby ocean.
Quick tests found between 3 and 24 becquerels of strontium and other beta-ray sources per liter of water in each of the seven areas. Those levels were lower than the legal limit of 30 becquerels of strontium per liter of water that can be released into the environment, TEPCO officials said.
Strontium is believed to accumulate in bones in humans and can cause bone cancer and leukemia.
TEPCO said its workers did not test radioactive cesium levels in the rainwater because the low strontium levels indicated there would be similarly low cesium levels present.
The utility said it did not release water from areas where high radioactive readings were registered. TEPCO said its workers were collecting water from such areas and transferring it into storage tanks.
For example, 170,000 becquerels of radioactive strontium and other beta-ray sources were detected per liter of water in Area H4, where the 300-ton leak discovered in August occurred.
In a separate development, TEPCO said tritium levels remain elevated and fluctuating in groundwater samples from a test well near the tank that was the source of the leak in Area H4.
Samples taken on Sept. 14 from the well were found to contain 170,000 becquerels of tritium, a radioactive isotope of hydrogen, per liter, the utility said Sept. 16.
That level was up from 130,000 becquerels per liter on Sept. 12 and 150,000 becquerels per liter on Sept. 13, but the reading dropped slightly to 140,000 becquerels per liter in samples taken on Sept. 15, TEPCO added.