The Nuclear Safety and Security Commission (NSSC) has launched an investigation following a heavy water leak at Unit 4 of the Wolseong Nuclear Power Plant in Gyeongju, North Gyeongsang Province.

The NSSC stated that it received a report from Korea Hydro & Nuclear Power (KHNP) at 2:26 p.m. on July 1 that heavy water had leaked from the heavy water detritiation and recovery system of Wolseong Unit 4.

The heavy water detritiation and recovery system is a component designed to prevent the degradation of heavy water used as a reactor moderator and to recover heavy water contained in the ion-exchange resins used in the process.

Heavy water is an artificial form of water created by combining oxygen with deuterium, an isotope of hydrogen.

According to the report, KHNP confirmed that there was no further leakage after stopping the transfer of heavy water once the leak was detected.

KHNP reported that the leaked heavy water was collected in the internal sump tank of the reactor and did not leak to the outside environment.

As of 9:00 p.m. on July 1, the amount of the leak was estimated at approximately 208 kg.

Wolseong Unit 4 has been in a state of reactor shutdown since it entered planned preventive maintenance in July of last year.

The NSSC stated that it has confirmed there are no abnormal radiation-related issues outside the power plant.

The NSSC added, "Our regional office has verified the safety of the site, and we plan to dispatch an investigation team composed of experts from the Korea Institute of Nuclear Safety to the scene."

(Photo: Provided by Korea Hydro & Nuclear Power, Yonhap News)