An estimated 300 tons of highly radioactive water has leaked from a tank at the stricken Fukushima nuclear plant, with much of the polluted water apparently seeping into the ground.
Tokyo Electric Power Co., operator of the Fukushima No. 1 nuclear power plant, said Aug. 20 it has been unable to specify the area of the tank from where the water leaked.
The utility is also checking for leaks at other tanks holding contaminated water at the site.
The water leaked from a 1,000-ton cylindrical steel tank, one of many located west of the No. 4 reactor. Part of the water remains pooled within a concrete barrier surrounding a group of 26 tanks.
The tanks hold radioactive water generated in the process of cooling the crippled reactors. The water has a concentration of 80 million becquerels per liter, which translates into 24 trillion becquerels for 300 tons.
A radiation level of 100 millisieverts per hour was detected near the surface of a puddle around the tank. The figure is 100 times the government’s annual limit of radiation exposure for the public.
A TEPCO employee on the morning of Aug. 19 found water flowing out from valves on the barrier. The leak created two puddles of a combined 120 liters outside the barrier.
TEPCO found that water levels at one of the tanks had dropped. The valves have been closed, and workers are pumping up water that remains within the barrier.
The water inside the tanks contains cesium, strontium, tritium and other radioactive materials, although cesium concentrations have been reduced through treatment.
The Nuclear Regulation Authority on Aug. 19 provisionally rated the incident as a Level 1 “anomaly” on the eight-level International Nuclear and Radiological Event Scale, one notch above Level 0 “deviations,” which have no safety significance.
The nation’s nuclear watchdog also instructed TEPCO to identify where the water leaked and collect soil contaminated by the radioactive water.
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