A nuclear reactor at an atomic power plant in Yeonggwang, South Jeolla Province, automatically stopped running Monday afternoon after its reactor protection system gave warning signals, the Korea Hydro & Nuclear Power Co. said.

The 1-million-kilowatt Yeonggwang-6 unit came to a halt at around 2:57 p.m., according to the company.

The unit had been under special treatment due to fuel rod defects that caused radioactivity levels in the reactor coolant to rise on April 30.

The KHNP said it was looking into what caused the malfunction and will resume the unit’s operation after gaining approval from the Nuclear Safety and Security Commission.

The Yeonggwang-6 unit began commercial operation in December 2002.

The nation’s maximum power supply capacity dropped to 75.45 million kilowatts as the Yeonggwang reactor stopped.

The electricity reserve and reserve rate remained at normal levels of 5.71 million kilowatts and 8.2 percent as demand dipped with the beginning of the peak summer vacation season. The likelihood of a power shortage will rise, however, if the Yeonggwang unit does not resume operation soon and the scorching heat wave continues.

The Kori-1 nuclear power plant unit in Busan remains idle after it was halted on March 13 due to a power failure amid growing public fears over nuclear safety. It is expected to resume operation early next month after a safety review by KHNP officials and experts recommended by local residents.

By Kim So-hyun (sophie@heraldcorp.com)