This is the sixth time that radioactive water has made its way into the sea from the plant, which was heavily damaged in the March 2011 earthquake and tsunami.
Tepco had raised the height of the weir in the ditch’s outlet from 70 cm to 85 cm, but it failed to prevent the latest outflow.
It occurred between 2:55 a.m. and 4 a.m., according to Tepco. The amount of outflow and the level of water contamination was unknown as of Monday evening.
Rainwater in the drainage ditch was to be transferred by pumps to a separate ditch leading to the plant’s port. Although eight pumps were operating at full capacity from 2:51 a.m., they were unable to catch up with the accumulation of rainwater due to heavy rain, allowing contaminated water to flow over the weir, Tepco said.
The company plans to complete its work by the end of March to close the drainage ditch’s outlet and make a new one inside the plant’s port.