The Nuclear Safety and Security Commission said it received a report from Korea Hydro & Nuclear Power Co. (KHNP) at about 2:26 p.m. on the 1st that heavy water had leaked at Wolsong Unit 4.
The leak occurred in the heavy-water downgrading and deuteration/de-deuteration system of the Wolsong Unit 4 coolant. This system prevents the heavy-water concentration from dropping when new ion-exchange resin is loaded into the resin column and recovers heavy water remaining in the resin when spent ion-exchange resin is discharged.
KHNP said it halted the transfer of heavy water immediately after confirming the leak and later reported to the Nuclear Safety and Security Commission that no additional leakage had been found. All the leaked heavy water was collected in the sump inside the reactor building and was estimated at about 208 kg as of 9 p.m. No release outside the plant was confirmed.
Wolsong Unit 4 is currently in planned preventive maintenance, with the reactor shut down. The Nuclear Safety and Security Commission said no abnormalities were found regarding external radiation from the plant.
At about 4 p.m. on the day, the Nuclear Safety and Security Commission conducted an on-site inspection through the Wolsong Nuclear Power Plant regional office and confirmed the safety status. It also plans to dispatch to the site an investigation team made up of experts from the Korea Institute of Nuclear Safety (KINS) to examine the specific cause of the leak and the condition of the equipment.