The environmentalist group issued video footage showing several of its members inside the fence of EDF’s Cattenom nuclear plant in northeast France, and launching several rounds of fireworks over the plant.

Local police said eight people had been detained. EDF said there had been no impact on Cattenom’s security and condemned Greenpeace’s intrusion as “irresponsible.”

“Do we need to wait for a malicious attack on a nuclear plant before EDF gets out of denial?” asked Greenpeace anti-nuclear campaign head Yannick Rousselet.

Read: For Sale: 2 Unused Nuclear Reactors in South Carolina

Olivier Lamarre, deputy head of EDF’s French nuclear fleet, said on a call with reporters that Greenpeace activists had broken through two barriers and reached the reactor’s nuclear zone to within a few tens of meters of the nuclear installations.

He said that as the activists had raised their hands in the air and unfurled a Greenpeace banner, police officials present on the site arrested them without violence within eight minutes.

“Had they been ill-intentioned people, or had there been a doubt about that, things would have happened differently and within a different timeframe,” Lamarre said.

Read: The U.K. Has Locked Itself Into Nuclear Power for 35 Years, but Wind Is Already Cheaper

Greenpeace this week published a report saying the spent-fuel pools of EDF’s nuclear reactors are highly vulnerable to attacks as their confinement walls have not been designed with malicious attacks in mind.

State-controlled EDF – whose 58 reactors provide three quarters of France’s electricity – denied its spent-fuel pools were at risk and said they had been designed to withstand earthquakes and flooding as well as terror attacks.

EDF also said this week it was repairing pumping station pipes at 20 nuclear reactors after discovering they might not be strong enough to resist earthquakes