A series of breakdowns of nuclear reactors and power plants is fueling concerns over power shortages this winter despite Korea’s all-out efforts to increase supply and ward off a blackout.

On Wednesday morning, a 950,000-kilowatt nuclear reactor in Gori, South Gyeongsang Province, was brought to an abrupt halt due to a temporary overvoltage.

That came merely 12 hours after a reactor with a capacity of 1 million kilowatts in Uljin, about 330 kilometers southeast of Seoul, came to a standstill due to a momentary failure of a condenser for steam turbines.

In October, another nuclear reactor at the same plant shut down due to a malfunction of the coolant pump.

Korea Hydro & Nuclear Power Co., the state-run nuclear plant operator, said it is working to figure out the details of Tuesday’s stoppage, adding that the incident “had no impact on any radiation leakage.”

The recent incidents cast a blight on Korea’s reputation as a new leader in nuclear power plant construction and the government’s efforts to stabilize electricity supplies for this winter.

Korea runs 20 nuclear reactors. The first reactor in Gori began operation in 1972.

Atomic power accounts for about 40 percent of the country’s total electricity supply, government figures showed. The plants have not had any major accident in the past 30 years.

Including the two recently put out of action, currently five reactors remain dormant. The other three ― two in Uljin and one in Wolseong, North Gyeongsang Province ― were closed for post-peak maintenance. The five’s combined capacity reaches 4.6 million kilowatts.

Jitters have grown over a possible electricity crunch since last week following a partial shutdown of a thermal power plant in Uljin and an unexpected power outage in Ulsan, which forced hundreds of petrochemical plants to freeze operations.

Authorities, however, see no immediate shortages at the moment.

“There’s no problem despite the breakdowns as we maintain the electricity reserves at nearly 6.8 million kilowatts,” the Ministry of Knowledge Economy said Wednesday in a statement. Reserves of 4 million kilowatts or higher are deemed sufficient.

On colder Thursday and Friday, the ministry added it will curb demand from large energy consumers and limit commercial and residential heating.

The KHNP also said it plans to resume operation of two of the reactors as early as next week, securing an extra 1.7 million kilowatts.

The ministry’s plan comes as part of its demand-cutting measures introduced last month to avert a possible blackout such as the one that hit the nation in mid-September amid an unseasonable heat wave.

The package includes a 10 percent demand cut for large factories and caps on maximum temperatures for commercial buildings and the use of neon signs.

Still, the ministry said it is having difficulty keeping up supplies, predicting peak demand shortage between the second and third weeks of January.

In mid-January, a 23-minute power failure triggered more than 70 billion won ($60.5 million) in losses at the country’s largest petrochemical complex in Yeosu, South Jeolla Province, as demand spiked to a record high of 73.14 million kilowatts.

By Shin Hyon-hee (heeshin@heraldcorp.com)