South Korea is facing increasing challenges in fully utilizing its nuclear and renewable energy sources due to strained transmission networks and delayed infrastructure expansion, leading to significant power reductions and growing concerns.
In Uljin, Gyeongsangbuk-do, the Hanul Nuclear Power Plant began reducing output for three of its reactors — Unit 6, Unit 2, and Unit 4 — starting from April 30. This reduction, known as “output control,” lowered power generation by 200 megawatts (MW) per unit, totaling 600 MW.
The measure was necessary as the transmission lines, which send electricity from the plant, had reached their maximum capacity. The situation grew critical after the power grid, which delivers electricity from the East Sea to the Seoul metropolitan area, became fully saturated by mid-April, leading to the shutdown of eight coal-fired power plants in Gangneung, Samcheok, and Donghae.
When the power grid equipment at the Sin-chungju Substation also broke down, the transmission system was severely strained. Consequently, the three nuclear reactors saw a significant drop in power output over five days, resulting in 29,600 megawatt-hours (MWh) of unproduced electricity—equivalent to the monthly electricity consumption of 90,000 households (based on a four-person household).
The growing demand for electricity, driven by the expansion of artificial intelligence (AI) and the increasing adoption of electric vehicles, has underscored the importance of efficient power transmission and distribution networks.
However, delays in expanding these networks in S. Korea are forcing power plants, including low-cost nuclear facilities, to scale back operations. This year has seen particular concerns, as issues within the transmission and distribution systems themselves have become more frequent. It’s like having more cars on the road without expanding the highways, causing heavy traffic, while existing roads get even more clogged due to repair work.
Despite the global emphasis on nuclear power, which offers low fuel costs and high energy output, S. Korea is struggling to fully utilize its nuclear facilities. This is due to the lack of adequate power infrastructure, such as transmission and distribution lines.
According to data from the Korea Power Exchange (KPX) shared by Representative Kang Seung-kyu of the People Power Party, the forced reduction in nuclear power output between January and July this year resulted in the loss of 163,200 MWh of electricity.
This figure is double the amount lost in 2020 (82,200 MWh) and represents enough energy to power major industrial companies like S-Oil and SK Energy for two to three weeks. Traditionally, nuclear power plants, which operate steadily year-round except during maintenance, rarely needed to cut back on production. However, as transmission networks become increasingly strained and equipment failures rise, these issues are becoming more common.
On the East Sea, where multiple nuclear and coal plants are located, up to 6.4 gigawatts (GW) of electricity—equivalent to the output of four or five nuclear reactors—cannot be transmitted to the Seoul metropolitan area due to grid limitations. Similarly, in the Honam region, where nuclear, solar, and wind power are concentrated, up to 2.3 GW of electricity goes unused as it cannot be delivered to demand centers.
In addition to the Sin-chungju Substation incident, a breakdown at the Sin-jecheon Substation in July forced Hanul Units 1 and 6, as well as Shin Hanul Unit 1, to reduce their output.
Last year, the Hanbit Nuclear Power Plant in Yeonggwang, Jeollanam-do, had to reduce production five times during the spring due to the rapid expansion of renewable energy sources like solar and wind power.
A KPX official explained, “Not only is there a shortage of major transmission networks, which function like highways carrying electricity to the Seoul area, but there’s also a lack of key transmission lines within the Honam region. This forces us to reduce nuclear output to accommodate renewable energy.”
As of the end of last year, S. Korea’s solar power generation capacity had surged 22-fold over the past decade, from 1,080 MW in 2013 to 23,900 MW. The rapid increase in renewable energy, such as solar power, without sufficient consideration for transmission infrastructure, has also led to a series of forced shutdowns.
A new system introduced last year allows solar power plants to be forcibly shut down like other energy sources, and this year has seen a significant rise in both the frequency and extent of these shutdowns. The amount of unproduced electricity due to forced solar plant shutdowns jumped to 4,982 MWh by July this year—17.4 times higher than the 283 MWh lost throughout last year.
Professor Yoo Seung-hoon of Seoul National University of Science and Technology emphasized, “This situation shows that without solving the problems in S. Korea’s transmission and distribution networks, it will be difficult to fully utilize both nuclear and solar energy. Expanding these networks should be a top priority.”
