Tokyo Electric Power Co. said Monday that about 203 tons of highly radioactive water was erroneously pumped to the wrong building at the crippled Fukushima No. 1 nuclear plant.
It is unlikely that the toxic water leaked beyond the building, however, because the radiation level of groundwater nearby hasn't changed yet. But the beleaguered utility is investigating why the pumps involved were turned on in the first place.
According to Tepco, the water contained 37 million becquerels per liter of radioactive cesium.
Beginning Thursday, the water level inside a building that was supposed to be receiving water started to go down and Tepco began an on-site investigation Saturday.
At 5 p.m. Sunday, it turned off four pumps it discovered operating. Workers also found later in the day that radioactive water was accumulating in the wrong building.
The four pumps were installed in June 2011, after the nuclear crisis erupted in the wake of Great East Japan Earthquake and tsunami on March 11 the same year. The pumps are designed to transfer water in emergencies but they had not been used before.
At the Fukushima plant, water used to cool three crippled reactors passes through several buildings and then undergoes a process to reduce its radiation. Part of the water is recycled as a coolant, and the remainder is stored in tanks.