Tokyo Electric Power Company’s (TEPCO) spokesperson, Masayuki Ono said a valve had accidentally been left open, causing the radioactive water to leak from the tank.
Ono said the contaminated water did not leak into the nearby Pacific Ocean.
‘’We are taking various measures, but we apologize for worrying the public with such a leak," Ono said.
A massive earthquake and a tsunami hit northeastern Japan in March 2011, causing meltdowns at three reactors at the Fukushima plant in one of the worst nuclear accidents since Chernobyl in 1986.
The leak is one of the worst since last summer when about 300 tons of radioactive water dripped from a tank.