The density of tritium in samples of sea water doubled in the past 10 days to a record 1,100 Becquerels per liter, an indication contaminated ground water may be seeping into the Pacific Ocean, the company reported Monday.
The reading remains far below the legally permitted level of tritium of 60,000 Bequerels per liter, The Japan Times said.
The announcement came after Tokyo Electric detected high levels of tritium and strontium in ground water at the plant, the Kyodo news agency said.
The company said Monday it was analyzing water for strontium-90, a radioactive isotope absorbed though the food chain, and thus a potentially greater hazard than tritium, the Japan Times said.
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