Heavy water leak at Wolsong Unit 4 triggers nuclear safety probe

A heavy water leak inside the reactor building of Wolsong Nuclear Power Plant Unit 4 has prompted the Nuclear Safety and Security Commission to launch an investigation.

The commission said it received a report from Korea Hydro & Nuclear Power Co. (KHNP) that heavy water had leaked from the coolant heavy water upgrading and downgrading system of Unit 4 at around 2:26 p.m. Wednesday.

The coolant heavy water upgrading and downgrading system prevents a drop in heavy water concentration when new ion exchange resin is loaded into the ion exchange resin column, and recovers heavy water contained in spent resin when it is discharged.

KHNP halted the transfer of heavy water immediately after detecting the leak, confirming that no further leakage occurred. The leaked heavy water — approximately 208 kilograms in total — was fully collected in the reactor building sump and did not escape to the outside, the company said.

Unit 4 was already shut down for scheduled maintenance at the time of the incident, and no abnormal radiation readings were detected outside the plant.

The commission said it plans to dispatch an investigation team of experts from the Korea Institute of Nuclear Safety to the scene to determine the cause of the leak.