The Nuclear Safety and Security Commission announced on May 26 that it had received a report from Korea Hydro & Nuclear Power stating that, during transformer replacement operations (power source switching) for electrical equipment maintenance at the Hanul Unit 1 nuclear power plant in Uljin County, North Gyeongsang Province, a circuit breaker failure occurred, resulting in the emergency diesel generator being unable to supply power to the safety bus.
According to the commission, between 10:47 a.m. and 11:20 a.m. that day, one of the two emergency diesel generators started up normally. However, during the process of restoring the power system, a circuit breaker failure prevented power from being supplied to the safety bus. Korea Hydro & Nuclear Power made its initial telephone report at approximately 2:15 p.m. and submitted a formal report to the commission as a reportable event at 8:30 p.m.
Hanul Unit 1 has been undergoing scheduled preventive maintenance since May 23, with the reactor in a shutdown state. Power was being supplied normally to the other of the two safety bus systems, so it was confirmed that there was no impact on the safety of the nuclear power plant.
The commission stated that it would dispatch an investigation team composed of experts from the Korea Institute of Nuclear Safety (KINS) to the site to conduct a detailed inspection of the cause of the incident and the safety of the equipment.
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