Tokyo Electric Power Co. said Sunday it had detected a high level of tritium in water under its stricken Fukushima No. 1 power plant.
Tepco detected 8.7 million becquerels of tritium per liter in water taken Friday from a cable trench running under the turbine building of the No. 2 reactor at a point about some 50 meters from the Pacific Ocean. The reading is 145 times the legal limit.
While tritium is a common hazard at nuclear power plants, the revelation came a day after the utility announced that the same water sample contained 2.35 billion becquerels of cesium and 750 million becquerels of other, unnamed radioactive substances, including strontium, that emit beta rays.
All would likely pose a higher risk of cancer if ingested by humans.
Tepco has been unable to figure out why the groundwater is being tainted with radiation. Its latest theory appears to be that the water in the observation wells on its premises is being tainted by water from the cable trench.
Last week, Tepco admitted that groundwater tainted with radioactive substances leaked into the Pacific from the plant and that the water level in the wells was rising and falling with the ocean tides.