Nuclear power is often discussed as a global technology, but its geography is remarkably concentrated. According to US Energy Information Administration analysis of International Atomic Energy Agency data as of June 2025, there are 416 operating power reactors in 31 countries, with a combined net capacity of 376 gigawatts. Five countries, the United States, France, China, Russia and South Korea, account for 71 per cent of that capacity.
That concentration has deep historical roots. Most large fleets were built in a burst of construction between the late 1960s and 1990, often in direct response to the oil shocks of the 1970s. What is changing now is where new construction is happening, and the answer points to a very different nuclear map by the late 2030s.
The incumbent fleets
The United States still has the largest fleet. Utilities operate 94 reactors, most built between 1967 and 1990, and nuclear supplied 19 per cent of US electricity in 2024. US plants produced 30 per cent of global nuclear electricity in 2023, and the fleet ran at a capacity factor of 92 per cent in 2024, which the EIA attributes to better management of planned and unplanned outages. The US fleet's strength is its operating performance, not its growth. New construction has been rare and expensive.
France is the second-largest fleet and the largest in Europe, with 57 reactors and 63 gigawatts of capacity. Its story is the clearest example of nuclear as an energy security policy: 52 reactors were built between 1975 and 1990 after the oil crisis. Nuclear supplies close to 65 per cent of French electricity.
France also shows how operational recovery can matter as much as new build. Corrosion problems discovered from 2021 cut French nuclear output sharply. In 2024, as EDF resolved those issues and made maintenance outages more efficient, nuclear generation rose from 320 terawatt-hours in 2023 to 361 terawatt-hours, even though installed capacity did not change until Flamanville 3 was added in December 2024. Hydropower also recovered, from 58 to 75 terawatt-hours.
The effect on Europe's power market was large. French cross-border electricity deliveries rose 48 per cent, from 70 terawatt-hours in 2023 to 103 terawatt-hours in 2024, according to the EIA's reading of ENTSO-E data. Exports to Belgium and Germany grew most, and Spain, previously France's largest source of imports, became a net importer from France. Gross French imports halved. A healthy French fleet is a regional asset, and its 2022 troubles were a regional problem.
China: the growth engine
China is the fastest-growing nuclear country in the world. It has commissioned 57 reactors since 1991, and according to IAEA data cited by the EIA, another 28 reactors with a combined 30 gigawatts are under construction. Once those are complete, China's installed capacity would surpass France's, leaving only the United States ahead.
Yet nuclear supplied only about 5 per cent of China's electricity in 2023. The scale of the Chinese power system means that even a world-leading construction programme makes only a modest difference to the national mix. Nuclear in China is less about displacing coal on its own than about adding firm, low-carbon supply alongside a much faster build-out of wind and solar.
China has also built a domestic supply chain by absorbing foreign technology. It acquired reactor designs from France, Canada and Russia, and has adapted the Westinghouse AP1000 into its own CAP1000. That domestic capability lowers construction costs and creates export potential.
Russia and South Korea: the exporters
Russia operates 36 reactors with 27 gigawatts of capacity and has 4 more units, about 4 gigawatts, under construction. Rosatom is replacing older RBMK graphite-moderated units with VVER-1000 and VVER-1200 light-water designs. More significant for the world market, the EIA describes Russia as the largest vendor of nuclear generating technology. A reactor sale is not a one-off transaction. It typically brings decades of fuel supply, servicing and often financing, so a vendor's market share translates into long-lasting relationships.
South Korea's programme, started in the 1970s, is driven by energy security and a desire to limit dependence on imported fuels. It operates 26 reactors with 2 more under construction. Its state-backed vendor, Korea Hydro and Nuclear Power, built the Barakah plant in the United Arab Emirates and has been selected as vendor for the Dukovany expansion in the Czech Republic. South Korea is the main non-Russian, non-Chinese vendor with a record of delivering a large multi-unit plant abroad.
Japan: the restart country
Japan sits outside the top five but remains a large nuclear country in suspended form. Before Fukushima, 54 reactors supplied about 30 per cent of its electricity. By the end of 2024, 14 had restarted, including Onagawa 2 and Shimane 2, the first boiling water reactors to return. Three more units have regulatory approval and about 10 others are under review. Nuclear supplied about 6 per cent of Japan's power in 2023, and the government's draft seventh energy plan sees it providing 20 per cent of energy supply in 2040. If restarts continue, Japan could re-enter the ranks of the largest operators without building a single new plant.
Why fleets age together
The construction burst of 1967 to 1990 has a consequence that is easy to overlook. Reactors built in the same two decades reach the end of their original licences at roughly the same time. For the United States and France in particular, the question of whether to extend, refurbish or retire large parts of the fleet arrives in a compressed window. Decisions on licence extensions, major component replacement and the timing of new build are therefore linked: every reactor that runs longer buys time for replacements to be planned and financed, and every early closure shortens that window. Japan's stated aim of extending operating lives beyond 60 years shows that the issue is now policy as well as engineering.
What the concentration means
Three conclusions follow. First, the global capacity ranking will shift toward China during the 2030s, on the strength of a construction pipeline no other country matches. Second, the market for new reactors abroad is dominated by Russia, with China and South Korea as the main alternatives and Western vendors trying to re-establish themselves. For buyers, choosing a reactor vendor is also choosing a long-term geopolitical partner.
Third, for the incumbent fleets in the United States and France, the most valuable nuclear capacity over the next decade is the capacity that already exists. France's 2024 recovery added more output in one year than many new reactors would. In the United States, high capacity factors and licence extensions keep a fleet built half a century ago at the centre of firm low-carbon supply. Running existing reactors well remains the cheapest nuclear power on offer.