Radioactive water exceeding safety standards spilled over storage-tank barriers at the Fukushima No. 1 nuclear plant and likely reached the ocean during a heavy rainfall on Oct. 20, the plant’s operator said.
The latest contaminated water leaks at the stricken plant came after workers were slow in removing water brought on earlier by Typhoon No. 26, Tokyo Electric Power Co. officials said Oct. 21.
Contaminated water breached the barriers at 11 locations during the Oct. 20 downpour, TEPCO said. The barriers surround large storage tanks filled with highly radioactive water.
Levels of strontium-90 exceeding provisional safety standards were detected at six of those sites. The highest reading in the spilled water was 710 becquerels per liter, 71 times the safety standard approved by the Nuclear Regulation Authority, according to the TEPCO officials.
The TEPCO officials said radioactive substances that had accumulated on the ground’s surface likely mixed with the rainwater, leading to the high strontium reading.
At all 11 locations, cesium-134 was below detectable levels, TEPCO said. At one site, the company recorded 12 becquerels of cesium-137 per liter, well within the safety standard of 25 becquerels.
The officials said the radioactive water possibly leaked into the sea via a drainage ditch.
As Typhoon No. 26 hit the plant on Oct. 16, the utility discharged the accumulating rainwater that was threatening to spill over the barriers. They measured radioactivity levels in the water within the barriers, and judged that the water was well within the provisional safety standards, according to TEPCO.
But according to a new protocol, the workers should have transferred the rainwater to small temporary storage tanks to determine radioactivity levels before the discharge.
After the typhoon passed the facility, TEPCO workers started pumping the rainwater within the 30-centimeter-high barriers into storage tanks.
However, due to a shortage of pumps, radioactive water exceeding 20 cm remained within some of the barriers when the downpour hit on Oct. 20, the officials said.
TEPCO measured radioactivity levels in water within the barrier walls, and it again opened valves to discharge the water when the readings were well under the safety standards.
But the rainwater breached the barriers at the 11 locations before the workers could transfer it to the small storage tanks or measure the radioactivity levels.
TEPCO plans to assess the impact on the sea of the latest water leaks.
The company said it intends to erect new barriers that are 60 to 130 cm high around the tanks to back up the existing 30-cm ones. But the higher barriers will not be completed until the end of the year.
Typhoon No. 27 is now approaching Japan. The utility on Oct. 21 started adding more pumps and pipes to quickly transfer the radioactive water within the barriers to temporary storage tanks.
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