Heavy rainfall from Typhoon No. 26 forced Tokyo Electric Power Co. to abandon protocol to prevent rainwater from overflowing near tanks holding contaminated water at the Fukushima No. 1 nuclear power plant.
TEPCO skipped newly introduced procedures when it discharged rainwater that was accumulating within the barrier walls that surround the storage tanks on Oct. 16.
The company said the radiation levels of the rainwater discharged from nine locations were all within provisional safety standards approved by the Nuclear Regulation Authority late on Oct. 15.
TEPCO originally told the NRA it would transfer accumulating rainwater to a temporary storage tank in order to determine radiation levels before releasing it to the outside.
However, the rainfall from the typhoon was too great, leaving workers no choice but to abandon protocol and discharge the water onto the surrounding ground.
Radiation levels were measured directly in the water accumulating behind the barriers before it was released.
“Rainwater was about to overflow from the barriers,” a TEPCO official said. “We checked (radiation levels) after mixing water taken at several locations.”
TEPCO said the water that exceeded safety standards was directed to holding tanks, including a previously shuttered underground tank. The company stopped using underground facilities after radioactive water escaped from some in April.
But workers resorted to the stopgap measure because they had no time to transfer all of the rainwater to a farther 4,000-ton tank.
TEPCO collected 1,400 tons of contaminated rainwater during Typhoon No. 18 on Sept. 15. The amount of contaminated water is expected to increase further with each heavy rainfall.
TEPCO plans to install a new gutter system to prevent rainwater from accumulating behind the barriers.
The utility will also erect concrete barriers measuring 60 to 130 centimeters high around the tanks in addition to the existing 30-cm-high barriers. But the new barriers will not be completed until the end of the year.
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