Almaraz unit 1 reactor shuts down automatically in Spain, Portugal sees no impact

What happened

The operator of the Almaraz nuclear plant in Cáceres, Extremadura, notified Spain's Nuclear Safety Council (CSN) on Thursday, 5 November 2026, that the reactor of Unit I had stopped automatically. According to the Portuguese Environment Agency (APA), the shutdown took place at 10:29 Spanish time while the unit was operating at full power. The stop followed a halt of the main turbine, which the CSN said was set off by the activation of a protection device on the alternator. Unit II, the plant's other reactor, continued running at 100% of its power. The plant sits close to the Portuguese border.

Cause and regulator's assessment

The root cause is the activation of an electrical protection on the main transformer, and that point remains under investigation. Based on the information available so far, the CSN classified the event as level 0 on the International Nuclear and Radiological Event Scale (INES). The regulator also said the incident had no impact on the safety of the installation, the people in it or the environment. In its press note, the CSN put it this way:

“The safety systems acted as foreseen in the design of the installation, and the plant is in a safe shutdown.”

The operator is carrying out the checks needed to confirm that the equipment involved is in the correct condition.

Plant status and restart

The operator reported that Unit I's parameters are stable and that its technical team is checking the equipment before the unit can be restarted. The notification to the CSN was made under the established procedure and the guidelines in force. The operator also said the incident had no effect on plant workers, the public or the environment. The sources do not give a date for reactivation of Unit I. Unit II is operating normally at 100% of its power.

Portugal's response

The APA said that, with the information available, the situation shows no consequences for Portugal that would justify additional protection measures for the population or the environment. Its note, released late on Thursday, said the protection systems worked as planned and the unit is in safe shutdown conditions. The agency is keeping watch through its Emergency and Radiological Protection Department, including the findings of the Spanish investigation. Environmental radiation is monitored permanently across Portuguese territory through the national RADNET network, whose data is publicly available. The APA said it will publish further information whenever relevant developments occur.

Licence extension to 2030

In August 2026, Spain's Ministry for the Ecological Transition and the Demographic Challenge (MITECO) renewed the operating authorisation for Units I and II of the Almaraz plant until June 2030. The ministry justified the measure by pointing to gas price instability caused by the crisis in the Middle East. The decision closed a process that had been formally opened in October 2025. The unit's stoppage on 5 November came months after that renewal.