Global highlights for 2025
Nuclear generation in different geographical regions
Nuclear reactors supplied a total of 2702 TWh of electricity in 2025, up 35 TWh from 2667 TWh in 2024, thereby setting a new annual record for global electricity supply.
Figure 2.1 shows the long-term development of global nuclear electricity generation. Nuclear energy was first used for electricity in the mid-1950s. It did not, however, make a significant contribution to global electricity supply until a period of rapid growth in the 1970s and 1980s. Growth then slowed through to 2006, followed by a five-year period in which global output fell, primarily because of lower generation in West & Central Europe. Generation then fell sharply in 2011 and 2012 following the accident at Japan’s Fukushima Daiichi plant.
Since 2012, global nuclear output has again trended upwards, with particularly strong growth in Asia, where output rose by approximately two-and-a-half times between 2012 and 2025. This growth has been led by the rapid expansion of nuclear generation in China, alongside new reactor starts in India, Pakistan and the United Arab Emirates.
Since 2012, nuclear generation in North America, South America and Africa has remained broadly stable, while East Europe & Russia has seen a gradual increase. West & Central Europe has continued to record declining generation, with Germany closing all its reactors and older reactors closing in Belgium, Sweden, Switzerland and the UK.
The contribution of nuclear to electricity supply
Nuclear generation supplied 9% of the world’s electricity in 2025. Although generation in absolute terms is at an all-time high, nuclear’s share of the electricity mix has declined from around 17% in the mid-1990s, because overall electricity supply has grown faster than nuclear generation.
Figure 2.3 places nuclear generation in the context of overall electricity demand, illustrating that nuclear output is at a record high while its share of global electricity supply has declined from its mid-1990s peak.
The contribution of nuclear to mitigating climate change
Since 1970, nuclear generation has avoided an estimated 43.6 billion tonnes of carbon dioxide emissions relative to generating the same amount of electricity in gas-fired power plants. At current generation levels, nuclear avoids the emission of around 1.25 billion tonnes of carbon dioxide each year. This is more than the combined annual CO2 emissions from the aviation and shipping sectors.
Compared with coal-fired power plants, which are more carbon-intensive, nuclear generation has avoided 97.2 billion tonnes of CO2 emissions. This cumulative total is greater than emissions from the entire energy sector in 2025 (38.1 billion tonnes CO2).
Composition of the global nuclear fleet
The current fleet of nuclear power reactors is dominated by large-capacity units. At the end of 2025, global net operable capacity was 400 GWe, up from 398 GWe in 2024.
The majority of electricity production comes from reactors that have been in service for between 30 and 50 years. However, the increase in the number of new reactor start-ups since 2015 is reflected in the rising proportion of electricity generation from reactors that have operated for less than a decade.
Most reactors in use today are pressurized water reactors (PWRs), which emerged as the predominant reactor type in the 1970s and have continued to increase in number. The next most common reactor types are boiling water reactors (BWRs) and pressurized heavy water reactors (PHWRs), although the number of reactors using these designs has declined in recent years.
The first generation of reactors built in the 1950s and 1960s were small compared with most reactors built later, with capacities below 500 MWe. Larger reactor designs were deployed during the 1970s and 1980s, offering the potential for greater economies of scale.
Although most reactors on which construction started in the past decade have capacities above 1 GWe, some smaller reactors continue to be built. Significant future deployment of small modular reactors (SMRs) would increase the number of new smaller-capacity reactors, but larger reactors are likely to continue to account for most capacity added to 2050.
Changes to the global nuclear fleet in 2025
Three reactors were connected to the grid in 2025, one each in China, Russia and India. Construction times differed significantly, from 62 months for Zhangzhou 2 in China to 163 months for Rajasthan 7 in India. The shorter construction period in China is consistent with the benefits of an active new-build programme based on standardised designs built in series.
Seven reactors shut down in 2025, including three units in Belgium and three small units at Bilibino in Russia. The Bilibino reactors had reached the end of operations, however, whereas the other four reactors were closed as a result of political decisions.
Eleven reactors started construction in 2025, matching the total in 2024. Nine of the new reactors to start construction were in China and two in Russia. Over the last 40 years, this number of new construction starts has been exceeded only in 2009 and 2010.
Meeting the target of tripling nuclear capacity by 2050 would require construction start rates to accelerate to around six times current levels by the mid-2030s.
Most reactors under construction today began construction within the last ten years. Among those that have been under construction for more than ten years, most have experienced periods of suspension. Only the PFBR prototype in India has had a continuous construction period longer than ten years.
Nuclear reactor capacity factors in 2025
In 2025, the global average capacity factor was 83.7%, up from 82.9% in 2024, continuing the trend of high-capacity factors recorded since 2000. Capacity factors in this section are based on the performance of reactors that reported electricity generation in the relevant calendar year.
Average capacity factors have increased steadily in each decade since the 1970s, with the greatest improvements taking place in the 1980s and 1990s. Capacity factors have continued to improve in subsequent decades, and the capacity factor deciles in 2025 were broadly similar to those in recent years.
The influence of length of operating life on age-related performance
There is no overall age-related decline in nuclear reactor performance as measured by the average capacity factors achieved by reactors of different ages. Figure 2.11 shows the average capacity factor for each reactor age over the six-year period from 2020 to 2025. The strong performance of reactors that have operated for more than 40 years demonstrates that reactor age does not, by itself, prevent strong performance during extended operation.
Extending the operating lifetimes of nuclear power plants is among the most cost-effective ways of securing additional low-carbon generation, according to the International Energy Agency.
In August 2026 the mean age of the world’s operable nuclear power reactors was 33 years. There were 46 operable reactors that commenced operation more than 50 years ago, representing around 10% of currently operable reactors.
The average age at which nuclear reactors have been permanently shut down has been steadily increasing over time. The average age of those reactors permanently shut down in 2025 was 48.7 years, up on the average of 47.3 years for 2024.
