Korea clears Kori-3 and Kori-4 nuclear reactors to restart, boosting AI power supply

Korea's ambitions to become an AI and semiconductor powerhouse gained a potential new source of electricity Tuesday as regulators approved two idled Kori nuclear power plant units in Busan to operate for another decade beyond their original lifespans.

The Nuclear Safety and Security Commission on Tuesday approved a request from Korea Hydro & Nuclear Power (KHNP) to keep Kori-3 and Kori-4 operating, with the majority of commissioners voting in favor of the plan.

Kori-3 and Kori-4 had been shut down after their 40-year operating licenses expired in September 2024 and August 2025, respectively. But with the new approval, Kori-3 is now authorized to operate until Sept. 28, 2034, and Kori-4 until Aug. 6, 2035.

The reactors cannot return to service immediately because years of shutdown have left them in need of equipment inspections and replacement of aging parts.

“We aim to restart the two reactors in phases during the first half of 2027,” the KHNP said.

Industry observers expect the reactors to resume commercial operations as early as February or March next year.

The decision marks Korea's fourth approval for extended nuclear reactor operations, after Kori-1 in 2008, Wolsong-1 in 2015 and Kori-2 in 2025. The latest extension is also the second such approval under President Lee Jae Myung's administration.

AI data centers are driving much of the pressure on Korea’s electricity supply. A single facility requires between 500 megawatts and 1 gigawatt of power, roughly equivalent to the electricity consumption of an entire small or midsize city. As more centers are built, demand is set to climb sharply, and the country’s current generation capacity and power grid are not yet equipped to keep up, leaving the government to tap every available source.

Korea stands to regain 1.9 gigawatts of reliable electricity generation capacity through continued operations at Kori-3 and Kori-4. More than a decision to prolong the lives of two aging reactors, the authorization demonstrates the potential of existing nuclear facilities to help stabilize power supplies, cut generation costs and increase energy efficiency.

The financial toll of prolonged reactor shutdowns has been considerable.

The four idled reactors — Kori-3, Kori-4, Hanbit-1 and Hanbit-2 — had missed out on approximately 1.9 trillion won ($1.42 billion) in potential electricity sales through Sept. 22, according to KHNP data obtained by Democratic Party Rep. Hwang Jung-a.

The losses highlight the steep opportunity costs associated with delays in regulatory approval.

The move signals a shift from policy to action for the Lee administration, which aims to meet surging power demand driven by AI growth through greater reliance on existing nuclear reactors that have cleared safety reviews.

Kori-3 and Kori-4 each have a generating capacity of 950 megawatts, exceeding Kori-2's 650-megawatt capacity, which received approval to extend operations last November. Together, the two reactors have a combined capacity of 1.9 gigawatts — enough to power 19 large AI data centers rated at 100 megawatts each.

“Continued nuclear operations provide a cost-effective way to deliver electricity promptly and reliably,” said Moon Joo-Hyun, an energy engineering professor at Dankook University. “They will make a significant contribution to Korea's power supply.”

The reactors will not, however, receive a full decade of additional electricity generation. The 10-year extension includes the period they remained shut down during regulatory reviews. As a result, a restart early next year would leave Kori-3 with only about seven years of actual operation and Kori-4 with about eight. Nuclear industry leaders say the rules should change, either through 20-year extensions like those in the United States and Japan or by counting the additional years from the restart date rather than the original license expiration date.

“Maintaining a reliable power supply requires legal changes that would allow nuclear reactors to obtain extensions before their operating licenses expire or continue operating for another 20 years under a single approval,” Moon said.

Another expert echoed the need to cut unnecessary administrative delays. “Once a panel of experts has completed its safety assessment, the administrative process should be shortened as much as possible,” said Chung Bum-jin, a professor of nuclear engineering at Kyung Hee University.

Regulatory approval for Kori-3 and Kori-4 could also give fresh momentum to efforts to extend the operating lives of other aging nuclear plants.

The next major decision will concern Hanbit-1 and Hanbit-2 in Yeonggwang County, Jeonnam-Gwangju, which used the same design as the Kori plants.  The commission is scheduled to review the continued operation of the Hanbit plants in the first half of 2027.

The Hanbit nuclear power plants are also gaining importance as a reliable electricity source for a planned semiconductor cluster in the Jeolla region. Unlike the 13 reactors found in North Gyeongsang, Hanbit is located in Jeonnam-Gwangju.

Reactors Hanul Nos. 1 and 2 in Uljin County, North Gyeongsang, and Wolsong Nos. 2-4 in Gyeongju, North Gyeongsang, are due for regulatory review as their operating licenses near expiration. Wolsong-2 is scheduled to shut down on Sunday.

Globally, nuclear plant operators are increasingly turning to life extensions rather than relying solely on new construction. A total of 240 of the 438 reactors in operation worldwide had been approved for continued service, and 213 were already operating beyond their original licensed periods as of the end of last year. That represents 55 percent of all operating reactors with such approvals. By using existing facilities, countries can secure power supplies without the higher costs and longer lead times associated with building new nuclear plants.

“A reactor's design lifespan is determined by commercial considerations, not safety limits,” Prof. Chung said. “Given the scale of planned data centers and the significantly lower cost of nuclear power compared to renewable energy, extending the operation of existing reactors is a logical step.”

The continued operation of aging nuclear reactors is expected to help ease strains on Korea's power supply. Ten reactors designated for operating extensions have a combined capacity of 8.45 gigawatts, equivalent to about 6.2 percent of the country's projected effective generating capacity in 2030, according to data from KHNP. The group includes Kori-2, Kori-3 and Kori-4, all of which have received regulatory approval.

Nuclear industry estimates suggest that replacing this capacity entirely with renewable energy would require more than twice the 39 gigawatts of additional renewable capacity outlined in Korea's 11th basic plan for long-term electricity supply and demand.

The government laid out plans in June to build 8.4 gigawatts of AI data center capacity by 2029 under the first phase of a sweeping megaproject. The proposed facilities will be located in Ulsan, Donghae in Gangwon, Sejong in the Chungcheong region and other parts of the country.

Another 10 gigawatts of capacity is envisioned by 2035, centered on sites secured by SK hynix. That would bring the combined electricity requirement of the two initiatives to 18.4 gigawatts — enough to require the construction of about 13 units of Korea’s advanced APR1400 nuclear reactors, each with a generating capacity of 1.4 gigawatts.

The focus now turns to the 12th basic plan for long-term electricity supply and demand, which will determine how much new nuclear generating capacity the government intends to pursue. The Lee administration is weighing additional reactor construction through a public consultation process despite its broader policy of expanding renewable energy.

“The world is moving toward a mix of renewables and nuclear power to cope with surging electricity demand, and Korea has no choice but to follow that path,” said Climate, Energy and Environment Minister Kim Sung-whan.

The approval does not resolve all the safety concerns surrounding the reactors. During Tuesday's deliberations, some commissioners who opposed the extension questioned whether regulators had sufficiently assessed the risk of simultaneous accidents at multiple reactors on the same site and the effects of climate change. The Kori plant also faces an approaching shortage of spent-fuel storage capacity, which raises the question of where to store additional radioactive waste.

 BY KIM MIN-JEONG, AHN HYO-SEONG [[email protected]]