It is thought the toxic water overflowed after a valve was left open by mistake, Fukushima operator Tokyo Electric (Tepco) said.
Spokesman Masayuki Ono told reporters: “We apologise for worrying the public with such a leak. Water is unlikely to have reached the ocean as there is no drainage in that tank area. We are now in the process of recovering the leaked water and the earth it has contaminated.”
Early indications suggest the leak occurred when contaminated water was accidentally pumped into an overfilled storage tank.
We are deeply embarrassed that this sort of unacceptable event would occur. Zengo Aizawa
Zengo Aizawa, executive vice-president of Tepco, added: “We are deeply embarrassed that this sort of unacceptable event would occur after the many steps we have taken to improve the management of stored water.
“We will therefore conduct a thorough investigation into what occurred and determine what additional steps must be taken to prevent any similar occurrence in the future, and will further strengthen field management of stored water. It also demonstrates the need for a permanent solution to the contaminated water issue.”