The operator of Japan's stricken nuclear power plant said Saturday that a high level of radioactive substances had flowed to the sea from a pit near a reactor intake, DPA reported.
Tokyo Electric Power Co said the amount was about 100 times the permissible level, but lower than earlier leaks from the Fukushima Daiichi plant in April.
The operator said a total of 250 tons of water flowed out to the sea from 2 am on May 10 to 7 pm on May 11.
The plant was damaged by the March 11 earthquake and tsunami and has leaked radioactive substances since then.
A steel float arrived near the plant by sea Saturday to store low levels of radioactive waste water.
The 136-metre-long, 46-metre-wide "mega-float" has a capacity to hold 10,000 tons of water. It was moved from its home port in Shizuoka prefecture, where it was used as a fishing park.
The operator lacks tanks to store 1 million of litres of highly contaminated wastewater seeping from leaks in reactor buildings at the plant.