KyodoTEPCO. has seen a rise in the level of radioactive tritium in seawater within the harbor at the crippled Fukushima No. 1 nuclear power plant.
A sample collected Friday contained around 1,100 becquerels of tritium per liter, the highest level detected in seawater since the nuclear crisis at the plant started in March 2011, the utility said Monday.
An official of the Nuclear Regulation Authority said groundwater containing radioactive substances may be seeping into the harbor from the plant site and there is a need to carry out a careful investigation because the data collected so far are limited.
The sample with the highest tritium concentration was collected near a water intake on the east side of the reactor 1 turbine building. Its level was more than double that of a sample taken on June 10 in the same area.