NUCLEAR ENERGY IN SPAIN

Nuclear energy in Spain: a key technology for the stability, autonomy and reliability of the Spanish electricity sector

Nuclear energy in Spain contributes around 20% on average to the energy mix, making it a key component of the electricity system not only as a source of generation, but also as a guarantee of stability and reliability in the face of disturbances or network fluctuations. It also helps mitigate global warming as it does not emit greenhouse gases.

Aerial view of the Cofrentes nuclear power plant, with two cooling towers and the surrounding mountain landscape.

Cofrentes Nuclear Power Plant, in Valencia.

Nuclear energy is one of the main sources of electricity generation in Spain: of the total electricity produced in the country in 2025, around 20% on average came from nuclear power, making it the second most important source after wind energy (21.6%). It is also the source that operated the most hours at full capacity, according to data from Red Eléctrica de España (REE).

Today, nuclear energy plays a particularly important role in the national energy mix, as it guarantees the stability and reliability of the electricity system and contributes to tackling climate change by not emitting greenhouse gases or other combustion products during operation.

In this article, we explain everything you need to know about nuclear energy in Spain, from its historical development and the benefits it brings to the electricity system, to the nuclear power stations operated by Iberdrola España.

What is nuclear energy

Nuclear energy is released from the central part of atoms (the nucleus), which is made up of protons and neutrons, through the processes of fission or fusion.

The first, nuclear fission, is the most widely used method worldwide for generating electricity. It consists of a reaction that occurs when the nucleus of heavy atoms – such as uranium or plutonium – is bombarded with neutrons, causing it to split into two or more smaller nuclei. At the same time, a large amount of energy is released along with two or three neutrons, which can in turn trigger further fission when they collide with other nuclei. This is known as a chain reaction, which releases energy in the form of heat and radiation that is ultimately converted into electricity in a nuclear power plant.
Nuclear fusion is still in the research and development phase due to its complexity, but it has promising potential. It involves a reaction in which two light atomic nuclei combine to form a heavier nucleus, releasing a large amount of energy (four times greater than nuclear fission reactions). For this to happen, extremely high temperatures (above 100 million degrees Celsius), high pressure and sufficient confinement time are required to contain the plasma – a hot, charged state of matter in which fusion occurs. The fuel used in fusion is deuterium and tritium.

The key role of nuclear energy in the Spanish energy mix

In Spain, nuclear energy is one of the main sources of electricity generation. According to the Spanish electricity system report 2024 prepared by Red Eléctrica, nuclear energy accounted for 19.97% of the total energy mix (52,391 gigawatt-hours (GWh) out of a total of 262,247 GWh), with only 5.37% of the country’s total installed net capacity. What’s more, in 2025, of all the electricity generated in Spain without emissions (74.53% of the total), nuclear production accounted for 25.58%.

Therefore, nuclear energy plays a highly significant role in Spain’s energy mix – that is, the set of energy sources used to meet the country’s energy needs – reaffirming its position as a key ally in the fight against climate change.

Evolution and current situation of nuclear energy in Spain

At an international level, nuclear energy began to play a role in civilian use during the 1950s. Key milestones include the first generation of electricity from a nuclear reactor in 1951 in Idaho (United States), powering four 200-watt light bulbs; the connection of the Obninsk nuclear power plant (Russia) to the grid in 1954; and the commissioning in 1956 of the world’s first commercial nuclear power station, Calder Hall in north-west England.

During this period, Spain established the Nuclear Energy Board (JEN) as a research and development centre, marking the formal beginning of nuclear technology in the country. In 1955, a nuclear cooperation agreement was also signed with the United States.

In the 1960s, the United States launched the first nuclear programme aimed at electricity generation. Spain followed suit, and during this period nuclear energy was promoted as a means of generating electricity. Between the late 1960s and early 1970s, reactors were commissioned at Almonacid de Zorita (Guadalajara, 1969), Garoña (Burgos, 1971) and Vandellós I (Tarragona, 1972).

The 1980s were marked by the nuclear moratorium included in the 1983 National Energy Plan, which halted the construction of seven planned reactors. However, between 1983 and 1988, seven reactors whose construction was already advanced were connected to the national grid: Almaraz I and II (Cáceres), Ascó I and II (Tarragona), Cofrentes (Valencia), Vandellós II (Tarragona) and Trillo (Guadalajara). The Nuclear Safety Council (CSN) was also established in 1980 as an independent body responsible for nuclear safety and radiological protection.

The control room at the Cofrentes nuclear power plant, in Valencia

From the 1990s to the present, no new nuclear power plants have been built. In 1997, the moratorium ended, although the construction of new plants would ultimately require government approval through the Council of Ministers. Over the past 25 years, reactors commissioned in the 1970s have been progressively shut down.

With the approval of the National Integrated Energy and Climate Plan 2021-2030 (PNIEC) in March 2021, a phased shutdown of the nuclear fleet currently in operation in Spain was scheduled between 2027 and 2035. However, in the current geopolitical context, there is ongoing debate about a possible extension of the operating life of nuclear power plants beyond the planned closure timeline.

In this regard, international experience is particularly relevant: in most countries around the world, with the United States as the main benchmark, plants using the same technology as those in Spain are extending their operational lifetimes to 60 and even 80 years. This trend shows that Spanish nuclear power plants, after 40 years of operation, remain fully modern facilities, the result of a continuous process of incorporating technological and safety improvements from their commissioning through to the present day.

Benefits of nuclear energy in Spain

The benefits of nuclear energy in Spain

What role does nuclear energy play in energy transition and in the Spanish electricity system?

Here are its main benefits

Illustration with a large industrial plant featuring cooling towers releasing steam, several chimneys, energy structures, and a sun in the blue sky

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Guaranteed stability for the electricity system

Nuclear energy, as a synchronous energy source, is produced in electric generators at a constant speed and synchronised with the grid frequency, giving the electricity system greater stability and making it more reliable, like hydropower does, which is also synchronous.

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Response to grid disturbances or fluctuations

Nuclear energy doesn’t depend on weather conditions to be generated so it provides the electricity system with inertia to cope with possible fluctuations or disturbances in the grid.

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Contribution to energy resilience and decarbonisation

Nuclear power plants produce virtually no carbon dioxide (CO₂) while operating and throughout their life cycle, which helps to mitigate global warming, like renewable energies do. In 2025, of all zero-emission electricity generated in Spain (74.53% of the total), nuclear power accounted for 25.58%.

Nuclear power plants operated and co-owned by Iberdrola España

At present, of the 10 nuclear reactors built in Spain, seven remain in operation, located across the regions of Extremadura, Valencia, Catalonia and Castilla-La Mancha.

Iberdrola España, through Iberdrola Generación Nuclear has 3,177 megawatts (MW) of installed nuclear capacity in Spain through its participation in six of the seven operating nuclear power plants.

Nuclear power plants in the Valencia region

In the Valencia region, Iberdrola España operates and fully owns the Cofrentes nuclear power plant, located in the municipality of the same name.

It began operations in 1985 and currently has the highest installed electrical capacity in Spain’s nuclear fleet (1,092 MW). In 2025, the plant achieved a gross electricity production of 8,784 GWh, representing around 48% of the energy produced in the Valencia region.

Aerial view of a nuclear power plant with cooling towers emitting steam, surrounded by trees and mountains

Cofrentes nuclear power plant (Valencia – Valencia region)

Location: Cofrentes

Commissioning: 1985
Installed capacity: 1.092 MW

Nuclear power plants in Extremadura

The Almaraz nuclear power plant is located in the municipality of Almaraz de Tajo (Cáceres). Iberdrola España holds a 52.7% stake in units I and II (also known as Almaraz I and Almaraz II). Unit I entered commercial operation in 1983 and unit II in 1984.

With an installed capacity of 1,049.40 MW, Almaraz I achieved a gross electricity production of 7,969 GWh in 2025. Almaraz II, with a capacity of 1,044.50 MW, produced 7,400 GWh. Together, Almaraz accounted for around 7% of Spain’s annual electricity demand in 2025.

Aerial view of a nuclear power plant next to a river, with two large reactors and an electrical substation

Amaraz I nuclear power plant (Cáceres – Extremadura)

Location: Almaraz de Tajo

Commissioning: 1983
Installed capacity: 1.049,40 MW

Nuclear power plant with a large structure and domes on the building, surrounded by vegetation and mountains in the background

Almaraz II nuclear power plant (Cáceres - Extremadura)

Location: Almaraz de Tajo

Commissioning: 1984
Installed capacity: 1.044,50 MW

Nuclear power plants in Cataluña

In Catalonia, Iberdrola España has stakes in two nuclear power plants: Vandellós II and Ascó II.

The Vandellós II nuclear power plant is located in L’Hospitalet de l’Infant (Tarragona). Iberdrola España holds a 28% stake. It has been in operation since 1988 and has an installed capacity of 1,087.1 MW. In 2025, it generated 7,392 GWh.

The Ascó plant is located in the municipality of Ascó, in the Ribera d’Ebre region (Tarragona). It has two units: Ascó I, which began operations in 1984, and Ascó II, which started in 1986. Iberdrola España holds a 15% stake in Ascó II, which has an installed capacity of 1,027.21 MW and generated 7,280 GWh in 2025.

In 2025, the three Catalan reactors accounted for 8.6% of total net electricity production in the peninsular system and up to 58.8% of electricity generated in Catalonia.

Nuclear power plant located by the sea, with the cooling tower visible and mountains in the background

Vandellós II nuclear power plant (Tarragona - Cataluña)

Location: Ribera d'Ebre

Commissioning: 1986
Installed capacity: 1.087,1 MW

Nuclear power plant with a cooling tower releasing steam, located by a river with mountains in the background

Ascó II nuclear power plant (Tarragona - Cataluña)

Location: Ribera d'Ebre

Commissioning: 1986
Installed capacity: 1.027,21 MW

Nuclear power plants in Castilla-La Mancha

In Castilla-La Mancha, Iberdrola España holds a 49% stake in the Trillo nuclear power plant, located in the municipality of the same name.

It began commercial operations in 1988 and has an installed capacity of 1,066 MW. In 2025, it generated 7,500 GWh, covering around 3% of Spain’s annual electricity demand.