The authorities are looking into a possible leakage after some 2.3 tons of stored water was released from spent fuel storage at the Wolseong No. 4 nuclear power plant in southern South Korea, officials said Saturday.

The Nuclear Safety and Security Commission (NSSC) said it received the report on the discharge of the water into the sea from the Korea Hydro & Nuclear Power Co. (KHNP), the operator of the Wolseong plant, at 7:53 a.m.

KHNP discovered a decrease in the water level of the spent fuel storage at 4:34 a.m. and immediately took measures to stop the leakage.

The radiation from the suspected leakage was estimated at 0.000000555 millisievert (mSv), far below the average radiation dose limit of 1 mSv to an individual for one year.

An NSSC official said the agency suspects there was a problem between the coolant water, used to cool the spent fuel, and the device used to cool this coolant water.

"We have blocked the storage to prevent any further leakage and are investigating the exact cause," the official said.