Tokyo Electric Power Co. said Dec. 6 that 150 liters of water containing strontium leaked from a water treatment facility in the Fukushima No. 1 nuclear power plant and flowed into the Pacific Ocean.
The amount of water, roughly equivalent in volume to an oil drum, contained 26 billion becquerels of radioactive materials, a level that could pose a risk to human health.
The stricken facility is located about 500 meters from the shore.
It was the first such leak since highly contaminated water in the No. 2 and No. 3 turbine buildings seeped into the sea via pits in April and May, respectively.
In those two instances, an estimated 770 tons of water containing 4,720 trillion becquerels of radioactive materials reached the sea.
In the latest case, the leak occurred in a processing facility to remove radioactive cesium from water used to cool fuel rods in nuclear reactors. This involves evaporating the water to remove the salt content.
TEPCO, operator of the stricken facility some 220 kilometers northeast of Tokyo, said the leak occurred Dec. 4.
At precisely what point during the processing that the leak occurred remains unclear.
Initially, it was suspected that 45 tons of radioactive water had leaked from the facility. A subsequent investigation found that 15 tons had leaked.
Of that amount, 240 liters seeped through a crack in a concrete wall. TEPCO said 90 liters of radioactive water accumulated in the building that houses the facility and the remaining 150 liters flowed into the sea.
After stanching the leak, TEPCO took water samples from the gutter to check for the presence of radioactive materials, including strontium, which emits beta rays.
It then determined that the water contained 490 million becquerels of radioactive materials per liter, or more than 3 million times the normal level found in the gutter. The contaminated water apparently mixed with rainwater when it flowed into the sea.
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