Around 30 activists from the environmental group invaded state-owned nuclear power utility Electricite de France's Tricastin power plant complex in southern France. They projected a video on the side of one of the plant's buildings that said "Tricastin Nuclear Accident" and showed the image of a giant crack forming across the building's facade.
Activists also hung a giant banner with President Francois Hollande's face and the words "President of the Catastrophe?"
France's nuclear safety authority said in a statement that so far the intrusion had no impact on the plant's safety.
By mid-afternoon, all of the activists had been arrested and were being held in a nearby police station, Greenpeace France said on its web site.
Speaking at a news conference President Francois Hollande said France "is very much attached to nuclear safety," and that everything was being done "to assure us that this nuclear safety is absolutely respected."
France is among the most nuclear-dependent countries in the world, with reactors producing about 80 percent of its electricity.
In 2008, the Tricastin plant reported several incidents that angered anti-nuclear groups, including a leak of unenriched uranium into two nearby rivers and the release of radioactive particles from a pipe.
Copyright 2013 The Associated Press.