Tokyo Electric Power Co. said Thursday it has detected high levels of radioactive cesium in water taken from deep under its disaster-hit Fukushima No. 1 nuclear plant.
Tepco found that water in a hole dug for a cable pipe contained up to 950 million becquerels of cesium per liter.
The pipe is located near another at the turbine building of reactor 2, where water has been found to contain high levels of radioactive substances.
Tepco said it believes this water was among the first contaminated in the early stages of the March 2011 meltdowns.
Studying water taken from 1 meter, 7 meters and 13 meters underground at a point some 65 meters from the Pacific, Tepco found 950 million becquerels of cesium and 520 million becquerels of beta ray-emitting radioactive substances, including strontium, in the water from 13 meters underground.
Water from 1 meter down contained 340 million becquerels, and a sample from 7 meters down contained 350 million becquerels.
Salt concentrations in water from 13 meters down were more than 10 times higher than water from 1 meter and 7 meters underground.
On July 26, Tepco detected 2.35 billion becquerels of cesium in water collected from a different cable trench closer to the ocean. Cesium, a metallic element, is subject to gravity.
It has already been widely reported that highly radioactive groundwater from under the plant had been flowing to the Pacific and that test wells dug near the shore showed water levels in the wells rose and fell with the tides, revelations Tepco has been criticized for being late to report.