A group of Greenpeace activists were able to climb their way into a French nuclear power plant, raising questions about safety and security at the facility. The French activists say all of the country’s nuclear reactors are vulnerable to attack.

Four eco-activists scaled the walls of the Cruas-Meysse plant in the southeastern Ardeche region. The building they were able to gain access to contained pools used to cool highly radioactive spent fuel rods. Once inside, the Greenpeace activists set off flares.

[VIDÉO] Nos militants en action ce matin pour dénoncer le #RisqueNucléaire. La sécurité de millions de citoyens européens est en jeu. pic.twitter.com/345U5NnmyE — Greenpeace France (@greenpeacefr) October 12, 2017

Police arrested 22 activists who participated in the stunt. France's state-owned energy giant EDF, which operates the Cruas-Meysse plant, confirmed there had been a break-in but said the breech posed no threat to the plant's safety.

The stunt is part of a Greenpeace campaign aimed at showing that France’s 58 nuclear reactors have serious security vulnerabilities and would be easy to attack.

“All you need to do is make a hole (in the building) to start a fire,” Yannick Rousselet, Greenpeace France’s chief anti-nuclear campaigner told AFP.

#Nucléaire — En action à #CruasMeysse : nos activistes sont entrés dans la centrale en moins de 10 minutes. La démonstration est faite : ces piscines d'entreposage du combustible nucléaire usé, très mal protégées, sont très accessibles. #RisqueNucléairepic.twitter.com/2pfbg3tEwN — Greenpeace France (@greenpeacefr) November 28, 2017

France is completely dependent on nuclear power, with atomic plants providing 75 percent of the country’s electricity. However, many of the plants are outdated and were built before threats posed by Islamic State (IS, formerly ISIS) and other terrorist organizations became a serious security concern.

Around a third of all reactors in the country are set to be closed by 2025.