The Nuclear Safety and Security Commission (NSSC) announced today (October 7) that it has approved the restart of Hanul Unit 4, which had automatically shut down on August 19.

The automatic shutdown of Hanul Unit 4 was triggered by a malfunction in the generator circuit breaker's disconnector and the failure of the reactor power rapid reduction system to operate.

A disconnector is a device used to cut off the flow of electricity to protect workers from electric shock during circuit breaker maintenance, while the reactor power rapid reduction system quickly lowers reactor power when the turbine stops.

Through its investigation, the NSSC confirmed that the disconnector malfunctioned due to an electrical defect caused by a poor connection.

It also determined that the reactor power rapid reduction system failed to operate properly due to foreign matter entering the instrument.

The NSSC stated that it verified the proper replacement of the faulty equipment, the execution of integrity tests, and the establishment of preventive measures.

An NSSC official said, "We will continuously monitor the implementation of the recurrence prevention measures even after Hanul Unit 4 is restarted."

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