TOP 10 Countries by Nuclear Share in Power Mix (2025)
Nuclear power plays very different roles around the world. In some countries it is a niche low-carbon source; in others it is the backbone of electricity supply. This 2025 snapshot highlights the ten countries where nuclear has the highest share in the power mix, based on the latest available data (mainly 2023–2024) on the percentage of electricity generated by nuclear plants.
Why nuclear share – not just nuclear output – matters
Discussions about nuclear power usually start with absolute generation: which country produces the most terawatt-hours of nuclear electricity. But from a systems point of view, the share of nuclear in total generation is just as important. It tells us how deeply nuclear is embedded in a country’s power mix and how dependent grid stability is on reactor fleets.
High-share nuclear systems look very different from grids where nuclear is marginal. Reactors in France, Slovakia or Hungary typically run at high capacity factors – often around 80–90% – and provide large amounts of steady “baseload” output. Gas, hydro, interconnectors and in some cases renewables then play balancing roles on top of this stable nuclear core. In low-share systems, nuclear behaves more like one flexible low-carbon option among many.
The ranking below focuses on the structural role of nuclear. It highlights those countries where reactors are not just present, but central: they deliver a large fraction of annual electricity, anchor security of supply and shape long-term planning decisions on grids, flexibility and decarbonisation.
Where nuclear leads the power mix
The leaders by nuclear share are a mix of advanced European economies and a few smaller systems. In all of them, nuclear regularly provides more than one-third of total generation, and in the top two it supplies well over half. These shares are drawn primarily from 2023 data, with 2024 updates where available, and are presented as rounded ranges.
France remains the most nuclear-intensive large grid, with reactors supplying roughly two-thirds of electricity. Slovakia comes next with nuclear providing around three-fifths or more. Further down the list, countries like Hungary, Finland, Belgium and the Czech Republic also rely on nuclear for a substantial slice of their power, complemented by hydro, gas and growing renewables.
Approximate nuclear share in electricity generation in the latest available year (mostly 2023–2024). Values are rounded and based on World Nuclear Association, NEI, IEA and Our World in Data compilations; they should be read as indicative ranges rather than exact point estimates.
Top 10 countries by nuclear share of electricity (2025 snapshot)
The table summarises the ten leaders, combining their nuclear share with a short description of how reactors fit into the broader power system. Micro-states are excluded and figures are rounded for clarity.
In all of these countries, nuclear units tend to run at high capacity factors and provide firm, dispatchable output. That makes them central to adequacy assessments, even in systems that are rapidly adding wind and solar.
| Rank | Country | Nuclear share & role in the mix |
|---|---|---|
| 1 | France | Nuclear supplies roughly two-thirds of French electricity (~65–70%), making France the world’s most nuclear-intensive large grid. A fleet of 57 reactors provides around-the-clock baseload and a big part of mid-merit generation, with gas, hydro and growing wind and solar handling peaks and flexibility. |
| 2 | Slovakia | Slovakia generates around 60–65% of its electricity from nuclear plants, among the highest shares worldwide. New units at Mochovce have pushed the nuclear contribution higher, turning reactors into the dominant low-carbon source and allowing coal to shrink rapidly in the mix. |
| 3 | Hungary | The Paks nuclear plant provides about 45–50% of Hungary’s electricity. Its high capacity factors and stable output make nuclear the cornerstone of security of supply, while imports, gas plants and a fast-growing solar fleet cover the remaining demand and flexibility needs. |
| 4 | Finland | In Finland, nuclear covers around 35–40% of power generation, a share that increased after the large Olkiluoto-3 reactor entered commercial operation. Nuclear’s steady output complements abundant wind and bioenergy, reducing the need for fossil imports from neighbouring markets. |
| 5 | Belgium | Belgian reactors supply roughly 40–45% of electricity, even after the closure of several units. Ongoing life-extension decisions for key plants will determine how long nuclear continues to serve as a major source of low-carbon baseload alongside gas and renewables. |
| 6 | Czech Republic | The Czech Republic gets roughly around 40% of its electricity from nuclear, split between the Dukovany and Temelín stations. Nuclear pairs with coal, gas and rising renewables, and new-build plans aim to maintain or increase the share as coal capacity retires. |
| 7 | Slovenia | Slovenia’s single Krško plant, co-owned with Croatia, accounts for around one-third of national electricity generation. Together with hydro, it underpins a low-carbon mix, while interconnectors and imports help balance demand and maintenance outages. |
| 8 | Switzerland | Swiss reactors provide roughly 30–35% of domestic electricity. Nuclear and hydropower jointly deliver a very low-carbon mix, with high-availability nuclear units smoothing seasonal variations in hydro inflows and supporting exports across Central Europe. |
| 9 | South Korea | In South Korea, nuclear typically covers around 30–35% of generation. A large, standardised fleet runs at high capacity factors and provides stable baseload, while coal and gas still supply a significant share and renewables gradually expand from a low base. |
| 10 | Armenia | Armenia operates a single VVER unit at Metsamor that supplies around 30% of national electricity. Given limited domestic fossil resources, nuclear plays an outsized role in energy security, backed by hydro and imports from neighbouring systems. |
Patterns behind high nuclear shares
The list reveals three broad patterns. First, most of the leaders are relatively small or mid-sized electricity systems. It is easier to reach a 40–70% nuclear share when total demand is modest and a handful of large stations can cover a big part of the load. France is the main outlier: a large, industrialised economy that nonetheless chose to rely heavily on nuclear after the 1970s oil shocks.
Second, high nuclear shares are almost always the result of long-term policy consistency. Countries like France, Slovakia, Czechia or South Korea made strategic decisions decades ago to standardise reactor designs, develop domestic supply chains and keep fleets running at high capacity factors. That continuity has allowed them to amortise high upfront capital costs over many years of operation.
Third, nuclear does not exist in isolation. Even in very nuclear-heavy grids, hydropower, gas, interconnectors and now wind and solar play crucial roles in balancing. High nuclear shares therefore go hand in hand with strong system-planning institutions that can manage maintenance cycles, refuelling outages and seasonal demand patterns.
Country snapshots: different nuclear strategies
France and Slovakia: nuclear as the default baseload
France and Slovakia are the only countries where nuclear consistently provides more than half of total electricity. In both cases, large reactor fleets run as the main source of baseload, with renewables and gas filling in the rest. Their challenge in the 2020s is to maintain high availability while integrating more variable wind and solar without undermining reactor economics.
Central Europe: Hungary, Czechia, Slovenia
In Central Europe, Hungary, the Czech Republic and Slovenia use nuclear to offset coal and imported gas. Their reactors typically deliver between one-third and one-half of generation, with the remainder coming from fossil plants, hydro and growing solar. Lifetime extensions and new-build projects aim to preserve high nuclear shares as coal retires and electricity demand rises.
Nordic and Alpine models: Finland and Switzerland
Finland and Switzerland combine nuclear with large amounts of low-carbon hydro, wind and bioenergy. In both countries, nuclear offers firm capacity during long, dark winters when demand is high and hydrology can be tight. This combination helps keep system-wide emissions low while maintaining reliability in harsh climates.
East Asia and the Caucasus: South Korea and Armenia
South Korea operates one of the world’s most advanced reactor fleets, using nuclear as a workhorse for industrial demand while progressively reducing coal. Armenia, by contrast, relies on a single older unit that still covers about a third of national consumption. Both face strategic choices about replacing or expanding nuclear capacity as units age and climate targets tighten.
What this ranking tells us – and what it leaves out
A high nuclear share does not automatically mean low electricity prices or perfect reliability. Wholesale prices depend on many factors beyond generation mix: fuel and carbon costs, network tariffs, market design and the timing of new investments. Likewise, system reliability is shaped by grid strength, interconnections and the diversity of low-carbon sources, not just the presence of reactors.
The ranking also focuses solely on the power sector. Some of the leaders still have substantial emissions in transport, buildings and industry that must be tackled through electrification, efficiency and other low-carbon fuels. In nuclear-heavy systems, using surplus off-peak nuclear output to support heat pumps, electric vehicles or hydrogen production is an increasingly important part of long-term planning.
Finally, the numbers here are moving targets. Refurbishments, life-extension decisions, the ramp-up of new plants and the growth of renewables can all shift the nuclear share within a few years. The key structural signal, however, is clear: in this group of countries nuclear is not a marginal technology but a central pillar of the power mix.
Primary data sources
- World Nuclear Association, Nuclear Generation by Country and Nuclear Power in the World Today, including 2024 nuclear electricity production and share of electricity generation by country, used to derive the ranking and approximate percentage ranges. See: https://world-nuclear.org/.
- Nuclear Energy Institute (NEI), statistics on the top 15 nuclear generating countries by nuclear share in 2023, providing specific percentage values for France, Slovakia, Hungary, Finland, Belgium, Czech Republic, Slovenia, Switzerland, South Korea and Armenia.
- International Energy Agency (IEA), chart Share of nuclear energy in total electricity generation by country, 2023, and country-level electricity mixes for France, Slovakia, Hungary and Finland, used as cross-checks on nuclear shares and trends.
- Our World in Data, Share of electricity production from nuclear (1985–2024), based on Ember and Energy Institute data, providing a consistent time series of nuclear shares used to confirm the relative ordering of countries in the 2025 snapshot.
- National and regional sources such as RTE (France), Eurostat nuclear energy statistics for EU member states, and national statistics offices in Finland, Hungary and South Korea, used for contextual information on capacity factors, low-carbon shares and system-wide emissions.
