Review of nuclear energy

• In 2024, nuclear reactors supplied a record high of 2667 TWh, surpassing the previous peak of 2661 TWh in 2006.
• Nuclear accounts for 9% of global electricity, down from 17% in the mid-1990s, due to faster growth in overall electricity demand.
• Since 2012, nuclear output has risen, driven by growth in Asia (especially China, India, Pakistan, UAE, and reactor restarts in Japan).
• Most reactors currently operating and under construction are PWR reactors, with an average capacity of around 1 GWe.
• 67 GWe of new nuclear capacity is under construction globally, with China leading with 32 GWe; other major builds are in Egypt, India, Russia and Turkey.
• Recent construction has focused on reactors with capacities of 1 GWe or above, but some smaller reactors are under construction.
• Nuclear energy is primarily used for grid electricity, but also supports district heating, which is provided by ~15% of reactors, and desalination, which has been used more rarely, but has been carried out in India, Japan, Kazakhstan, Pakistan and Russia.
• The International Energy Agency’s Net Zero Emissions by 2050 Scenario projects nuclear capacity to reach over 1000 GWe by 2050. This is around 80% of the goal endorsed in the Declaration to Triple Nuclear Energy, which was launched at COP28 in Dubai in 2023.

 

1.1 How has nuclear generation developed in different regions?

In 2024 nuclear reactors supplied 2667 TWh of electricity – a new record for annual global electricity supply, surpassing the previous peak of 2661 TWh in 2006.¹ 

Nuclear generation was first used for electricity generation in the mid-1950s. However, it did not make a significant contribution to global electricity supply until a period of rapid growth in the 1970s and 1980s, followed by slower growth through to 2006, at which point annual nuclear generation remained broadly the same for five years.

There was a decline in global nuclear generation in 2011 and 2012, following the March 2011 accident at Japan's Fukushima Daiichi nuclear plant. Germany made the political decision to accelerate the shutdown of its reactors, shutting down eight reactors in 2011, with the remaining nine shutting progressively between 2012 and 2023.

In Japan, most reactors continued operating after the Fukushima Daiichi accident, but once they went offline for refuelling or other planned outages, they required a long process of authorization to restart under new regulatory conditions. As of September 2025, 14 reactors have restarted, with 11 reactors in the process of restart approval.

Despite the loss of output from Germany and Japan, since 2012 global nuclear output has again trended upwards, with particularly strong growth in Asia, where output has more than doubled. This has been led by the rapid growth of nuclear generation in China, as well as new reactor starts in India, Pakistan and United Arab Emirates.

Output has also risen steadily since 2012 in East Europe & Russia, with new reactor starts in Belarus and Russia.

Generation declined slightly in North America, with the start-up of three reactors in the USA against the closure of 13 reactors in the USA and three in Canada. In South America and Africa, generation has remained broadly constant.

In West & Central Europe output from nuclear power plants has declined. In addition to the 17 reactor closures in Germany, 12 reactors have closed in Belgium, Sweden, Switzerland and the UK compared to the start-up of just three, in Finland, France and Slovakia. However, that decline has been halted in the last two years, with output increasing, resulting in part from the return to service of reactors in France, which had had outages for repairs in 2022-23.

1.2 What contribution is nuclear making to energy supply?

Nuclear generation in 2024 supplied 9% of the world’s electricity. While generation in absolute terms is at an all-time high, the share of nuclear in the electricity generation mix has declined from around 17% in the mid-1990s, as overall electricity demand has increased more rapidly than the increase in nuclear generation.²

1.3 What reactors make up the current global nuclear fleet?

The current fleet of nuclear power reactors is dominated by large capacity units. As of 1 October 2025, there are 438 operable reactors, with a total capacity of 397 GWe.

More than 70% of operable reactors are pressurized water reactors (PWRs). Boiling water reactors (BWRs) account for 14%, pressurized heavy water reactors (PHWRs) for 11%, light water graphite moderated reactors (LWGRs) 2%, gas-cooled reactors (GCRs) 2%, and there are just two operable fast neutron reactors (FNRs) and one high-temperature gas-cooled reactor (HTGR).

In recent years the PWR design has been even more dominant, with 55 of the 59 reactors to enter service in the last ten years being PWRs.

1.4 What reactor sizes have been built?

There has been a trend towards larger reactor capacities, as reactor designs were developed during the 1970s, with larger reactors offering the potential of greater economies of scale. The mean average gross capacity for reactors entering their first year of operation reached 1000 MWe in the mid-1980s and has remained broadly at this level to the present day.

While less prevalent, smaller capacity reactors have continued to enter service, with recent examples being the two 35 MWe (gross) reactors of the Akademik Lomonosov floating nuclear power plant and the 211 MWe (gross) Shidaowan HTGR unit. Significant future small modular reactor (SMR) deployment would see a resurgence in the number of new smaller capacity reactors, but larger reactors will likely continue to make up the majority of the overall capacity added.

1.5 What additional nuclear capacity is likely in the short term?

With average construction times of around 6-7 years, from first concrete to grid connection, additions to nuclear capacity by 2030 will be largely defined by reactors already under construction.

A total of 70 reactors, with a combined capacity of 78 GWe (gross) is currently under construction globally, with almost half, 38 GWe, located in China.

Egypt, India, Russia and Turkey each have around 5 GWe of nuclear capacity under construction, with other reactors under construction in Bangladesh, Brazil, Pakistan, Iran, Slovakia, South Korea and the UK. Reactors are also formally under construction in Argentina, Japan and Ukraine and Argentina, but these reactors are not currently being worked on.

In addition, three reactors in the USA currently shutdown are being prepared for restart: Holtec’s Palisades reactor in Michigan; Constellation’s Three Mile Island 1, which now forms part of the Crane Clean Energy Center; and NextEra's Duane Arnold in Iowa. A small number of other recently closed reactors could feasibly restart before 2030, if supported by policymakers and market conditions.

Most reactors currently under construction are large reactors, with capacities over 1000 MWe. As with recent startups, there are a small number of SMRs under construction, including first-of-a-kind units at Changjiang (ACP100, 125 MWe) in China and at Cape Nagloynyn (RITM-200S, 57 MWe) in Russia.

Most reactors under construction are PWRs. The only two BWRs listed as under construction are in Japan, where construction on both has been suspended since 2011.

1.6 What are the drivers for current and future use of nuclear technology

1.6.1 Reducing greenhouse gas emissions

Fossil fuels became the predominant source of primary energy at the start of 20th century, displacing traditional biomass.³ Currently, approximately three-quarters of global greenhouse emissions come from the burning of fossil fuels for energy,⁴ releasing enormous quantities of greenhouse gas into the atmosphere. Nuclear energy is an effective alternative source of low-carbon electricity and heat, with very low greenhouse gas emissions across the full life cycle.

The United Nation’s Intergovernmental Panel on Climate Change (IPCC) have concluded that human activities, principally through emissions of greenhouse gases, have ‘unequivocally’ caused global warming, with global temperatures between 2011-2020 being 1.1°C higher than the average temperature between 1850-1900.

The IPCC’s sixth assessment report concluded that:

“Continued greenhouse gas emissions will lead to increasing global warming, with the best estimate of reaching 1.5°C in the near term in considered scenarios and modelled pathways. Every increment of global warming will intensify multiple and concurrent hazards (high confidence). Deep, rapid, and sustained reductions in greenhouse gas emissions would lead to a discernible slowdown in global warming within around two decades”

Through the United Nations Framework Convention on Climate Change, governments have made commitments to address global warming, pledging in the Paris Agreement to “limit global temperature increase to well below 2 degrees Celsius above pre-industrial levels, while pursuing efforts to limit the increase to 1.5 degrees Celsius”. A total of 194 countries ratified the Paris Agreement, with only Libya, Yemen and Iran failing to do so. The United State withdrew during the first Trump presidency, but rejoined in 2021, before President Trump issued an executive order in 2024 for the United States to withdraw again at the start of his second term.

Climate models have projected many emissions paths that would be consistent with meeting the temperature goals of the Paris Agreement. In general, those consistent with keeping global temperatures rises below 2 degrees Celsius require greenhouse gas emissions to reach net zero^a by around 2075, with peak emissions before 2025, and those limiting temperature rises to 1.5 degrees Celsius require emissions to reach net zero by around 2050, with peak emissions before 2030.

In reality, greenhouse gas emissions have increased dramatically over the last 125 years, with carbon dioxide emissions rising from 2 billion tonnes CO2 in 1900 to 38 billion tonnes in 2023.

A major contributory factor to the increase in global greenhouse gas emissions has been the increase in demand for energy, met predominantly by fossil fuels. A reduction in global emissions on the scale required to meet the objectives of the Paris Agreement is unachievable without a rapid switch from unabated fossil fuels to sources with low greenhouse gas emissions. 

All forms of power generation have some greenhouse gas emissions associated with activities in their life cycle, but life cycle emissions analysis from the United Nations Economic Commission for Europe shows that emissions from nuclear are among the very lowest in comparison to other forms of generation, and two orders of magnitude lower than emissions from fossil fuels.⁶ Nuclear power plants also offer a large power output from a relatively small area. A large nuclear power plant occupies around 3 km², much less than that required for wind and solar.

In combination, these benefits make it clear that nuclear energy has an important role to play in meeting global greenhouse gas emissions goals. This was recognized in the Global Stocktake agreement, unanimously endorsed at the United Nations COP28 climate change conference in Dubai in 2023. That agreement recognized nuclear energy as a means to achieve ‘deep, rapid and sustained reductions in greenhouse gas emissions’.⁷

As discussed in section 1.6.2, efforts to reduce greenhouse gas emissions include greater electrification of the energy sector. Electricity is being applied to sectors such as transport, heating and industrial processes because of policy pressure to decarbonize, improving economics of technologies such as EVs and heat pumps, corporate and consumer demand and energy security needs. This will only be effective if the additional electricity demand is met from low carbon sources, such as nuclear.

The increasing adoption of electric vehicles is being met through additional electricity demand, reducing demand on petroleum products. According to the IEA, 18% of new car sales globally in 2023 were electric, with more than half being in China. This meant around 40 million electric cars were on the roads in total. IEA expects this to reach between 500-800 million electric cars by 2035.⁸ Zero emissions vehicle mandates, and policies to phase out new petrol or diesel car sales in some countries are driving this change.

Other uses of electricity are also drivers for increased nuclear generation. For heating and cooling in buildings, there is increasing adoption of heat pumps, driven by greater efficiencies and policy incentives.⁹ Fossil fuelled boilers and furnaces are being replaces with electric alternatives for industries such as food processing, chemicals, and textiles. Electric arc furnaces can replace blast furnaces for industries such as steel production.

Nuclear plants also offer the potential for greenhouse gas emissions mitigation through direct use of nuclear heat, rather than via the subsequent generation of electricity.

Nuclear technologies can be used to provide industrial process heat. In some cases, the outlet heat produced by conventional light water reactors is suitable. But for industrial processes requiring higher temperatures reactors such as high temperature gas cooled reactors will provide a suitable heat source.For some transport sectors direct electrification is not a simple alternative to the use of fossil fuels. For examples, in aviation, although some advances have been made for short haul flights, the power density of batteries makes them unsuitable for aviation.

Synthetic fuels may be made through the combination of hydrogen and carbon dioxide through Fischer-Tropsch synthesis, where the two gases are chemically combined under high temperature and pressure. The hydrocarbons produced are then refined to produce the jet fuel. 

In such cases, production of synthetic fuels may offer a carbon-neutral alternative to conventional fossil fuels, with nuclear process heat being used as a low-carbon energy source to drive the process under high temperature and pressure. The hydrocarbons produced are then refined to produce the jet fuel.

In such cases, production of synthetic fuels may offer a carbon-neutral alternative to conventional fossil fuels, with nuclear process heat being used as a low-carbon energy source to drive the process.

1.6.2 Meeting growing electricity demand

Economic growth, industrial development and higher standards of living require affordable and reliable energy supplies. Population growth and urbanization also drive increased demand for energy.

While some advanced economies have reduced their energy demand in recent years, with increasing pursuit of energy efficiency and the transfer of more energy intensive industry to emerging economy countries, global demand for energy has continued to rise.

In the 20th century primary energy consumption grew ten-fold, and has continued to grow in the 21st century. This growth in energy consumption is expected to slow, and under some scenarios decline.

According to the International Energy Agency, under its Stated Policies Scenario, final energy consumption would increase from 445 EJ in 2023 to 533 EJ in 2050. Under its Announced Policies scenario, consumption would fall slightly to 434 EJ and under its Net Zero Scenario consumption would fall more sharply to 344 EJ.

However, under all three scenarios electricity consumption increases, from 29,863 TWh in 2023, to 58,352 TWh, 70,542 TWh and 80,194 TWh in 2050 under the Stated Policies, Announced Policies and Net Zero Scenarios, respectively.¹⁰ The increase in the share of energy supply met by electricity is largely due to the use of electrification as a method of emissions reduction, as direct use of fossil fuels is replaced by electricity generated from low-carbon sources. Nuclear generation, as one such source, is predicted to see supply rise, to 4460 TWh, 6055 TWh and 6969 TWh under the three IEA scenarios. This pattern of increasing nuclear output to 2050 is reflected in many other scenarios and projections, this is described in more detail in Appendix 2.

1.6.3 Ensuring reliability of supply

The assurance of secure and reliable supplies of energy is essential in modern economies. As noted in Section 1.7.1, nuclear energy can help reduce overall system costs, for example by minimizing the need for large-scale energy storage and backup capacity. In systems with high shares of renewables, additional costs arise from the need to reinforce grids, invest in energy storage, and enhance system flexibility to manage intermittent generation. Nuclear provides continuous, dispatchable generation that complements intermittent renewables like solar and wind. 

Nuclear power plants contribute to grid inertia, which supports overall power system stability. Inertia is the kinetic energy stored in the rotating mass of large synchronous generators—such as those in coal, gas, hydro, and nuclear plants. When a sudden disturbance occurs (for example, the loss of a large generator), this stored energy resists rapid changes in frequency, slowing the rate of decline and giving grid operators time to take corrective action. By providing rotational inertia, nuclear plants help dampen frequency fluctuations and reduce the risk of cascading failures or blackouts. Because nuclear units typically operate continuously at high output, they offer a steady source of inertia. In contrast, systems dominated by inverter-based renewables such as solar and wind have lower inherent inertia and are more susceptible to rapid frequency deviations.

1.6.4 Strengthening security of supply

The inherent nature of different generation forms, in terms of carbon emissions or reliability of output, are key factors when assessing their merits. However, the impact of external factors on the ability to secure supplies of fuel, and the impact of supply issues on the price of electricity, are also important factors.

Geopolitics, sanctions and wars have all constrained supply and resulted in significant price volatility. The 1973 Yom Kippur War resulted in OPEC members cutting oil exports to the USA and allies supporting Israel. Oil prices quadrupled, sparking a global energy crisis. The 1979 Iranian Revolution and subsequent Iran-Iraq War and the 1990 Gulf War both led to oil prices doubling.

Recently, Russia’s invasion of Ukraine led to record-high gas and electricity prices in Europe. In addition to supply constraints, such as the transit of Russian gas through Ukraine, many European countries have sought to reduce their dependence on Russian gas supplies.

Oil and gas rely on pipelines, LNG terminals and shipping routes, all of which are potential vulnerabilities for supply chains. Oil can be stockpiled, but storage for natural gas is limited, which can restrict long-term resilience.

In comparison, nuclear fuel is extremely energy-dense, and each fuel assembly typically remains in the reactor for several years. Reactor operators usually acquire new fuel assemblies well ahead of refuelling and may also hold inventories of fresh fuel onsite, reducing the risk of short-term supply shocks.

Uranium is mined globally in countries such as Australia Canada, Kazakhstan and Namibia, and no equivalent of OPEC dominates supply, although some fuel cycle services, such as enrichment, do have a small number of major suppliers. Significantly, uranium fuel costs make up only a small share of nuclear electricity costs. Therefore, overall generation costs are not so strongly affected by changes in nuclear fuel prices.

1.7 The Declaration to Triple Nuclear Energy

In December 2023, at the United Nation’s COP28 climate change conference in Dubai, 25 governments signed the Declaration to Triple Nuclear Energy, committing themselves to supporting a global goal of tripling nuclear capacity by 2050.¹¹ An additional six governments joined the declaration at COP29 in Baku, Azerbaijan, and two more joined at COP30 in Belem, Brazil. The signatories to the declaration are: Armenia, Bulgaria, Canada, Croatia, Czech Republic, El Salvador, Finland, France, Ghana, Hungary, Jamaica, Japan, Kazakhstan, Kenya, Republic of Korea, Kosovo, Moldova, Mongolia, Morocco, Netherlands, Nigeria, Poland, Romania, Slovakia, Slovenia, Sweden, Turkey, Ukraine, United Arab Emirates, UK, and the USA.

The declaration recognized the key role of nuclear energy in achieving global net-zero greenhouse gas emissions by 2050, which would be needed to keep the goal of limiting global temperature increases to 1.5 °C within reach. The declaration also recognized nuclear energy’s role in supplying clean dispatchable baseload power, thereby strengthening energy security.

Also at COP28, 130 nuclear companies signed a pledge to support the tripling nuclear goal. Then at New York Climate Week 2024, 14 financial institutions declared their support and discussed how the finance sector could contribute to nuclear achieving the tripling goal. Later, at CERAWeek 2025 in Houston, Texas in March 2025, 14 companies representing large energy users also expressed their support for a tripling of nuclear capacity by 2050.

The target set in the governmental Declaration to Triple Nuclear Energy is based on a baseline of nuclear capacity in 2020, when operable nuclear capacity was 393 GWe. A tripling of this capacity would require operable capacity to reach nearly 1200 GWe by 2050. In the following chapters we review the technologies that will be used to meet these capacity goals. We will also review current nuclear capacity targets set by governments and examine whether, at a national level, there is sufficient ambition to meet the global tripling goal.