Tokyo Electric Power Co. said Sunday that 600,000 becquerels per liter of tritium has been detected in groundwater at the crippled Fukushima No. 1 nuclear plant.
It’s the first time such a high level of tritium, an isotope of hydrogen, has been measured in the plant’s groundwater, Tepco said.
The water, sampled Friday, came from an observation well about 6 meters west of the plant’s port. The well is the closest to the sea of the five wells used for radiation monitoring.
On July 1, the tritium level in the same well was 510,000 becquerels per liter, Tepco said.
The utility also said it had measured, on Wednesday, a seawater tritium level of 2,300 becquerels per liter — the highest so far — near the water intakes of reactors 1 to 4.
Tritium concentrations in groundwater have become denser on the north side of the intakes, but Tepco also said it has yet to determine whether the tainted water has been leaking into the sea.
A Nuclear Regulation Authority official recently said contaminated groundwater from the plant, which is being fed cooling water from outside, may be seeping into the ocean and that the matter must be addressed carefully because data is limited.