South Korea's nuclear fleet and grid: can they power AI?

South Korea wants 18.4 gigawatts of AI data centres by 2035, and its main firm power source is a state-run nuclear fleet of 26 operable reactors. The plan is not only about chips. It depends on reactor approvals, new units, a crowded grid and unresolved rules on power contracts.

This post looks at the supply side of that plan: what Korea can generate, what is stuck, and what the government has promised. It builds on our wider South Korea AI infrastructure overview and does not repeat it. Every figure is labelled by source and date, and this is a factual summary, not investment advice.

Key numbers at a glance

• 26 operable reactors with 25,609 MWe of capacity, 4 under construction with 5,360 MWe (World Nuclear Association country profile, page updated 2 October 2026).
• 185 TWh of nuclear output out of 643 TWh total in 2025, about 29 percent (World Nuclear Association, same page; the page's own summary says "about one third", so the two statements differ).
• About 85 percent nuclear capacity factor in 2025 (World Nuclear Association).
• 31.8 percent nuclear share targeted for 2030 and 35.6 percent for 2038 in the 11th Basic Plan for electricity, finalised February 2025 (World Nuclear Association).
• 28.9 GWe of nuclear capacity planned for 2030 and 35.2 GWe for 2038 under that plan (World Nuclear Association).
• 18.4 GW AI data centre target for 2035, with 8.4 GW by 2029 (Light Reading, 30 June 2026).
• 158 to 165 GW forecast peak electricity demand in 2040, described as 60 to 70 percent above current levels (Financial News editorial, 15 October 2026, citing a government forecast).
• 4 reactors idle while awaiting continued operation permits, with an opportunity cost the editorial puts at about 2 trillion won, or 5.1 billion won a day (Financial News editorial, 15 October 2026; this is an opinion piece).
• 9 reactors, 7.8 GW, about 30 percent of national nuclear capacity, are in or near the same review queue (same editorial).
• 170 MWe: size of the domestic i-SMR small modular reactor design, with design approval targeted for 2028 and commercialisation for 2035 (World Nuclear Association).
• 1,200 billion won: planned Science Ministry investment in three domestic small reactor designs by 2030, about 830 million US dollars (World Nuclear Association).
• About 20 times: how much more power an AI training server draws than a standard server, as stated in a Korea JoongAng Daily article of 16 June 2025 (a general industry statement, not a measured figure).

Why power is the first question

An AI data centre is a building full of accelerators, networking and cooling that runs around the clock. A gigawatt (GW) is one thousand megawatts, and a site that draws one gigawatt continuously uses about 8.76 terawatt hours (TWh) in a year. That is simple arithmetic on 8,760 hours, and real sites rarely run at their full rating every hour.

Apply the same arithmetic to the national target. If all 18.4 GW ran flat out all year, the load would be roughly 161 TWh. Treat that as an upper bound for scale, because the buildout is spread over a decade and utilisation will be lower. Still, compare it with the 185 TWh that the World Nuclear Association says Korean reactors produced in 2025. The target is large against the system that has to supply it.

The International Energy Agency's global estimate, quoted in an SK hynix article of 30 September 2026, puts worldwide data centre use at about 415 TWh in 2024, roughly 1.5 percent of global electricity, rising to about 945 TWh by 2030. SK hynix attributes the figures to the IEA, and they are relayed here second hand, so check the IEA original before reusing them. The same article says electricity use by accelerated servers is expected to grow about 30 percent a year from 2024 to 2030. The direction is clear even if the exact numbers are revised.

For Korea the question is where those megawatts come from, and when. The answer has three parts: existing nuclear, new nuclear, and the grid that moves the power.

The existing fleet: big, steady, and in a review queue

According to the World Nuclear Association, Korea has 26 operable reactors with a combined 25,609 MWe. Its page records 2025 output of 185 TWh out of 643 TWh, or 29 percent, at a capacity factor of about 85 percent. Capacity factor is the share of a plant's maximum possible output that it actually delivers. Eighty five percent is high and reflects steady baseload running, which is exactly the profile a data centre wants.

The state-owned Korea Hydro and Nuclear Power (KHNP) operates all of this capacity. The World Nuclear Association profile explains that KEPCO was the sole utility until April 2001, when its generation business was split into six companies and all nuclear capacity went to KHNP, the largest of them; KEPCO kept the transmission and distribution monopoly. The profile lists reactors at Kori, Saeul (the former Shin Kori 3 to 6), Hanul, Wolsong and Hanbit.

The fleet is aging. Reactors have a licensed design life, and operating beyond it needs a continued operation permit from the nuclear regulator. The Financial News editorial of 15 October 2026 describes where that stands. Kori 3 and 4 and Hanbit 1 and 2 have stopped because their design lives ended. Kori 3 shut in September 2024, Kori 4 in August 2025, Hanbit 1 in December 2025 and Hanbit 2 in September 2026. On 15 October the Nuclear Safety and Security Commission approved their accident management plans, but the continued operation permit for Kori 3 and 4 was not decided. The paper expects a decision as early as the following month.

Some detail from the same piece is worth keeping, with the caveat that it is an editorial and argues one side. It says KHNP submitted the accident management plan in 2019 and approval took about seven years. It says Kori 2 received its permit in the previous November, about a month after its plan was approved. It says five more reactors are waiting for review, among them Hanul 1 and 2 and Wolsong 2, 3 and 4, with Wolsong 2's design life ending in the following month. Together the nine reactors total 7.8 GW, which it puts at about 30 percent of national nuclear capacity.

The editorial's recommendations are about process, not safety limits. It argues for starting linked reviews 5 to 10 years before design life ends and counting the extended period from the permit date. Whether to accept those proposals is a policy decision that readers can weigh for themselves. The point for an AI reader is narrower: a large block of existing, reliable capacity is waiting on regulatory timing, and delays remove it from the system while demand grows.

New reactors: what is under construction

The World Nuclear Association lists four reactors under construction, all of the APR1400 design, a large Korean pressurised water reactor. They are Saeul 3 and 4 and Shin-Hanul 3 and 4, with construction starts on 1 April 2017, 20 September 2018, 20 May 2025 and 29 May 2026 respectively.

Saeul 3 reached first criticality on 12 April 2026. Criticality is the point at which a reactor sustains a chain reaction, and it comes before commercial power. The page says commissioning was interrupted by an automatic shutdown in August 2026 and a manual shutdown in September 2026. Saeul 4 awaits its operating licence. These are normal parts of bringing a unit online, but they show how far the first megawatt hour can be from the first announcement.

Beyond these four, the 11th Basic Plan calls for two more large reactors. The same source says the government confirmed in January 2026 that it would proceed with them, and that KHNP selected Yeongdeok in North Gyeongsang as the candidate site in June 2026. The page does not give an outcome for the 12th Basic Plan, covering 2026 to 2040, only that the energy ministry began a three month public deliberation on nuclear's role in September 2026.

Politics matters here. The same page says that President Lee Jae-myung, elected in June 2025, called nuclear power "inherently dangerous" during the campaign and said the nuclear heavy mix should be re-examined, with more priority for renewables. It then reports that after surveys showed strong public support for nuclear, his administration confirmed the two new reactors in January 2026. It also says responsibility for energy policy and for nuclear plant construction and operation moved in October 2025 to the Ministry of Climate, Energy and Environment from the former trade and industry ministry. A reader following AI power policy should therefore watch that ministry as well as the science ministry.

Small modular reactors: promising, and years away

A small modular reactor (SMR) is a reactor built in smaller units, often largely in a factory. Supporters hope it can be sited closer to demand and built faster. Korea has several designs in progress, according to the World Nuclear Association.

The page says the i-SMR, at 170 MWe, had a standard design approval application submitted in February 2026, with approval targeted for 2028 and commercialisation for 2035. The SMART100 received standard design approval in September 2024. Gijang in Busan was selected to host an SMR included in the 11th Basic Plan. A Special Act on SMR Development passed in February 2026, and the Science Ministry plans to invest 1,200 billion won by 2030 in three domestic designs.

Set those dates beside the data centre timetable. Phase 1 of the national AI plan targets 8.4 GW by 2029. Phase 2 runs from 2030 to 2035. A reactor targeted for commercialisation in 2035 cannot serve phase 1 at all and arrives at the very end of phase 2. That does not make SMRs irrelevant, because they may matter for later growth. It does mean the first wave of AI capacity must run on whatever generation and grid exist, or can be built, before 2030. Our companion piece on nuclear power for AI data centres worldwide compares how other countries handle the same gap.

The grid and the rules: where reporting finds the friction

Generation is only half the picture. Power must reach the site through transmission and distribution lines, and Korea's heaviest load is around Seoul.

A Financial News article of 5 April 2026 says the power grid is "already close to saturation" and that new data centre locations are limited by power system impact assessments and a lack of transmission and distribution infrastructure. It gives no numerical data on this. The government's response, as reported by Light Reading on 30 June 2026, is to push capacity outside the capital, with priority for Chungcheong, Ulsan, Donghae and Sejong, and to offer discounted electricity rates plus streamlined land and water rights. The Light Reading article does not mention nuclear or any specific power source.

The same April article describes a proposed Special Act on AI Data Centers as stalled over ministry disagreements. According to that report:

• The trade and industry ministry wanted broad allowance of direct power contracts, known as power purchase agreements or PPAs, and eased location rules. A PPA is a long contract that lets a large user buy electricity directly from a generator.
• The economy and finance ministry worried about power market distortions, lost tax revenue and the financial burden on state-run power companies, and wanted to limit tax benefits.
• The environment ministry wanted stronger environmental impact assessments because of power and water use.
• The science ministry wanted AI infrastructure treated as a national strategic technology, like semiconductors, to expand tax credits.

No later report cited here confirms whether the act has passed since April, so treat its status as open. Direct contracts matter because they decide whether a data centre developer can sign for a specific reactor or wind farm, or must buy from the regulated system at set tariffs.

The Stargate Korea story shows the same pressure in practice. A Korea JoongAng Daily report of 7 September 2026 says that a year after the October 2025 announcement, OpenAI, Samsung and SK had not settled sites, power supply or funding. An anonymous industry source quoted there said the companies were struggling to acquire a site with enough power and water. The companies' own statements were cautious: SK Telecom said no progress had been made since the memorandum of understanding, and OpenAI said the project was still under discussion.

Site choices that use what is nearby

Some projects try to match load to local energy. The Ulsan data centre planned by SK Group and AWS, reported by Korea JoongAng Daily on 16 June 2025 from industry insiders, sits on land in the Mipo National Industrial Complex near an LNG combined heat and power plant run by SK Gas. The article says cold energy released when LNG is vaporised can help cool the data centre. It reports about 40 MW operational by November 2027 and 103 MW by February 2029, with about 60,000 GPUs. These are insider figures and may change.

Co-location like this saves some cooling energy and may shorten the distance power travels. It does not remove the need for firm supply, and it ties the site to a fuel, LNG, whose price and supply are outside Korea's control.

There is also a Korean industrial angle on the equipment side. Korea JoongAng Daily reported on 19 October 2026 that LS Electric won a 170 billion won contract to supply 38 kilovolt switchgear for a hyperscale AI data centre of an unnamed US technology company, with supply starting next year. The company projects the US data centre power infrastructure market to grow 16 percent a year, from 13 trillion won in 2025 to 56 trillion won in 2035. That is a company projection. It shows that power equipment, not only chips, is part of Korea's AI economy.

What is firm and what is uncertain

Firm, because an official step or several consistent sources support it:

• Korea has 26 operable reactors and four large ones under construction.
• Nuclear supplied roughly 29 percent of 2025 electricity, per the World Nuclear Association table.
• The government announced the 18.4 GW AI data centre plan on 29 June 2026, with regional priority away from Seoul.
• The government confirmed two further large reactors in January 2026 and passed an SMR act in February 2026.

Uncertain or contested:

• How much of the 18.4 GW will be built, and how fast. The plan is a target, and the Stargate Korea example shows announcements running ahead of sites.
• Whether reactor permits arrive on time. The editorial claims delays are costly, and others may weigh review time differently.
• Whether direct power contracts will be allowed for data centres. The special act was reported as stalled in April 2026.
• The 12th Basic Plan outcome. Public deliberation began in September 2026 and no result had been reported as of 19 October 2026.
• Whether the 2040 demand forecast of 158 to 165 GW holds. It is a forecast quoted in an editorial, and the original government document is not cited here.
• The mismatch between "about one third" and 29 percent on the World Nuclear Association page. Different years and definitions may explain it; the page does not reconcile the two.

What to watch next

• The nuclear regulator's decision on Kori 3 and 4, and the order of the next reviews.
• Whether Saeul 3 reaches steady commercial operation after its 2026 shutdowns.
• The 12th Basic Plan, and what it says about how much new load is for data centres.
• Passage of an AI data centre special act and its power contract provisions.
• First megawatts online at flagship sites against the November 2027 target for Ulsan.
• Progress of the i-SMR design approval, targeted for 2028.

For teams adding data centre suppliers and equipment to their inventory, Safeguard offers SBOM and dependency scanning, with a free scan at https://gold.safeguard.sh/scan.

Quick check

Sources

• World Nuclear Association, Nuclear Power in South Korea (page updated 2 October 2026)
• Financial News, Four idle nuclear reactors need faster approvals for continued operation, editorial (15 October 2026)
• Light Reading, South Korea plans massive 18.4GW AI data center buildout by 2035 (30 June 2026)
• Fnnews, Korea AI data centre policy and power (5 April 2026)
• Korea JoongAng Daily, OpenAI's Stargate project in Korea stuck at starting gate (7 September 2026)
• Korea JoongAng Daily, SK Group and AWS to build Korea's largest AI data center in Ulsan (16 June 2025)
• Korea JoongAng Daily, LS Electric wins 170 billion won U.S. switchgear deal (19 October 2026)
• SK hynix, AI infrastructure insight on power and cooling (30 September 2026)

Last reviewed: 19 October 2026.