Greenpeace activists set off fireworks inside a nuclear plant in eastern France early Thursday after breaking into the facility to underline its vulnerability to attack.

The anti-nuclear group, known for its daring and often spectacular publicity stunts, said the fireworks were set off at the foot of a spent fuel pool -- where nuclear plants store highly radioactive fuel rods that are removed from reactors after their use.

"Our activists launched a firework in the perimeter of a French nuclear plant. These installations are vulnerable," the group said on Twitter, along with a video of the stunt at the plant in Cattenom, near the border with Luxembourg.

The tiny duchy's environment minister, Carole Dieschbourg, was "very worried over the huge security shortcomings" at the plant, her ministry said in a statement.

Operator EDF, France's state-owned energy giant, said police stopped the protesters eight minutes after the pre-dawn intrusion and that the plant's safety was not threatened.

Police said eight Greenpeace activists were in custody, and a local prosecutor said they faced five years in jail and 75,000 euros ($89,000) in fines.

On Tuesday, Greenpeace had warned about security shortcomings at French and Belgian nuclear plants, citing an expert report commissioned by the group.

Top EDF official Olivier Lamarre said in a conference call with journalists that the activists had "proved nothing, other than that the security detail worked perfectly."

Roger Spautz, a Greenpeace official in Luxembourg, said that about 15 activists crossed two security barriers to reach the building containing the spent fuel rods.

He told AFP the action was aimed at drawing attention to the "fragility" of the fuel tanks "that are not protected, unlike the reactor buildings".

- Built before Al-Qaeda -

Greenpeace tasked seven experts from France, Germany, Britain and the United States with looking at various attack scenarios involving nuclear plants in France and Belgium, some of which date back more than three decades.

France is the world's most nuclear-dependent country, with 58 reactors providing 75 percent of the country's electricity. Belgium has two nuclear plants.

The Greenpeace report noted that most of France's plants were built before the rise of threats from non-state terror groups such as the Islamic State group and Al-Qaeda and that their defences -- particularly of their spent fuel facilities -- were weak.

Environmentalists have long questioned the safety of France's vast nuclear network, but around a third of all reactors in the country are set to be closed by 2025 under government plans.

Nuclear power was once a source of national pride in France, but public support has fallen in line with other European countries after the disaster at the Fukushima plant in Japan in 2011.

EDF said in a statement that it was constantly evaluating its nuclear plants' resistance to criminal acts or terrorism.

Source: AFP