The Almaraz nuclear power plant is located in Caceres, Extremadura, Spain.
The Almaraz NPP is expected to be closed by 2028. Image courtesy of Iberdrola.
The Almaraz NPP uses water from the Arrocampo reservoir, which receives water from the Tagus River. Image courtesy of Osvaldo Gago.

The 2.1GW Almaraz nuclear power plant (NPP) located in Cáceres, Extremadura, is the oldest and the biggest nuclear power plant operating in Spain. It comprises two 1,050MW pressurised water reactor (PWR) units commissioned in September 1983 and July 1984, respectively.

Construction on the Almaraz NPP was started in 1973 under the joint ownership of three electric companies, namely Hidroeléctrica Española, Sevillana de Electricidad, and Unión Eléctrica Madrileña.

The facility is currently owned by Iberdrola (53%), Endesa (36%), and Naturgy (formerly Gas Natural Fenosa, 11%).

It is operated by Centrales Nucleares Almaraz-Trillo (CNAT), a joint operating company for both the Almaraz and Trillo nuclear power plants. CNAT comprises the owners of both the nuclear power facilities.

Almaraz nuclear reactors license renewal

In June 2010, the operating license for both the units of the Almaraz nuclear power station were renewed for ten years until June 2020.

Further, in March 2019, the plant co-owners decided to apply for license renewal until November 2027 for unit one and October 2028 for unit two, following the government’s decision of shutting down all NPPs in the country by 2035.

Iberdrola, Endesa, and Naturgy, in the same month, also agreed to invest up to £515m ($680m) to extend the operational life of the reactors until 2027 and 2028, respectively.

Spanish nuclear power plants closure schedule

The Spanish Government announced a schedule to close all the seven nuclear power reactors operating in five sites between 2025 and 2035, in February 2019.

Nuclear power accounted for approximately 7% of the total installed capacity and one-fifth of the country’s total electricity generation in 2018.

The decision to shift away from nuclear power generation aligns with Spain’s ambitious clean energy plan to be completely dependent on renewable energy sources by 2050.

According to the closure schedule rolled out by the government, Almaraz-I and Almaraz-II will be the first two reactor units to be shut down, followed by Asco-I (2029), Asco-II (2030), Coferentes (2033), Vandellos-II (2034), and Trillo (2035).

Almaraz NPP site and the controversy from Portugal

The Almaraz nuclear power plant is located on a 1,683ha-site in the Almaraz de Tajo area of Caceres Province, in the Extremadura region of Spain.

The site stretches over the municipalities of Almaraz, Saucedilla, Serrejón, and Romangordo.

The Almaraz NPP is located on the banks of the Arrocampo reservoir that serves as the source of cooling water. The Arrocampo reservoir is fed by the Tagus River, the longest river in the Iberian Peninsula that runs for more than 1,000km through Spain and Portugal.

Portugal alleges that the Almaraz NPP site is located in a seismic risk area approximately 110km away from the Portuguese border, while neither environmental impact assessment for the plant’s cooling system has been carried out nor any cross-border emergency plan been established.

Further, the Spanish Government’s decision in 2016 to construct a centralised temporary storage (CTS) facility for used nuclear fuel assemblies of Almaraz, as well as other Spanish NPPs, was opposed by the Portuguese Government through a case lodged against Spain in the European Commission in January 2017.

Almaraz nuclear power station make-up

The Almaraz nuclear power plant consists of two Westinghouse-design three-loop pressurised PWR units in two separate containment buildings. The rated thermal power of each unit is 2,956MWt.

Each cylindrical containment building has a semi-spherical dome and is made of reinforced concrete with carbon steel plate lining on the inner wall.

The reactor core of each unit is placed within a thick-walled and steel-lined airtight cylindrical pressure vessel. Each reactor core comprises 157 fuel assemblies that consist of 289 fuel rods each. The fuel rods are 4m-long and 10mm in diameter each and contain 4.5%-enriched U-235 fuel pellets inserted in Zirconium alloy.

The Almaraz NPP utilises the open-circuit cooling system, hence it doesn’t have any cooling tower.

Each unit of the plant has three cooling pumps and three steam generators. All of the plant’s six original steam generators supplied by Westinghouse were replaced with Siemens KWU 61W/D3 steam generators between 1996 and 1997.

The steam generated by each reactor drives the turbines housed within the adjacent turbine buildings for power generation.

The generated electricity is evacuated to the national grid via a 400kV switchyard. The power station also has a 220kV switchyard for sourcing offsite electricity, and five diesel generators, including one back-up generator for emergency power supply for the operations.

Spent fuel storage facility

The used fuel assemblies of each reactor unit are stored under water in the spent fuel pool in the fuel building located adjacent to the containment building.

The plant’s individual storage facility (ISF) for the under-ground storage of the used fuel assemblies in dry casks was inaugurated in December 2018.

Almaraz nuclear energy operations

The Almaraz NPP is a base power plant that operates with an average plant load factor of more than 86%. The safety reassessments carried out at the plant in the aftermath of the 2011 Fukushima Daiichi nuclear power plant disaster have confirmed that the safety measures adopted at the site are satisfactory.

Contractors involved

Empresarios Agrupados (EA) provided engineering, supply management, construction supervision, as well as testing and start-up services for the Almaraz NPP.

In 2014, Tecnica Reunidas was engaged for engineering and completion of design changes in the plant’s emergency refrigeration system, following the recommendations of the post-Fukushima safety assessments.

The company also designed, supplied, and commissioned electrical warming systems for the boric acid mix tanks at both the units of the plant in the same year.

IDOM was awarded the engineering, design, and work supervision contract for the alternative emergency control centre (AECC) at the power plant in 2014.

Spanish state-owned nuclear fuel manufacturer Enusa was awarded a new fuel contract for the Almaraz NPP in  November 2018.

Equipos Nucleares (Ensa), a wholly-owned subsidiary of Spanish public holding company Sociedad Estatal de Participaciones Industriales (SEPI) designed and supplied the casks for the transport and storage of used fuel assemblies at the independent spent fuel storage facility of the Almaraz nuclear power plant.

GDES Technology for Services (GDES T4S), a joint venture between Iberdrola and GD Energy Services, supplied the RESHAND robotic arm to the Almaraz nuclear power facility in November 2018. The robotic arm is used for handling radioactive waste at the plant.