The Japanese utility battling to bring its radiation-spewing nuclear reactor under control says it is moving 1,500 more tons of radioactive water into temporary storage.

Tokyo Electric Power Co. said Sunday that the move is critical to prevent the spilling of highly radioactive water into the ground and the sea.

More than 100,000 tons of radioactive water have pooled beneath the troubled Fukushima Dai-ichi nuclear power plant in northeastern Japan. TEPCO has said the water could start overflowing about June 20 — or possibly sooner with heavy rainfall.

The cores of three of the plant's reactors melted and sunk to the bottom of the units after the March 11 tsunami destroyed backup generators, damaging crucial cooling systems.