Paris ( CNN ) -- French police arrested dozens of Greenpeace activists Tuesday who had forced their way into a nuclear power plant . During the early morning break-in , the activists hung anti-nuclear banners from the Fessenheim plant , France 's oldest in operation and a flashpoint for anti-nuclear campaigners who say it is unsafe and should have been closed long ago . `` Today , militants of various nationalities , coming from all over Europe , protested and occupied Fessenheim , the oldest French nuclear center , '' Greenpeace said on its website . EDF , which operates the plant in eastern France , said 56 people had been detained . Local authorities said police remained on site as a precautionary measure . `` No activist entered inside the buildings . These events had no impact on the safety of facilities , which are operating normally , '' local authorities said in a written statement . Greenpeace wants Fessenheim , which has been in operation since 1977 , to be closed immediately . The activists hung a banner from the roof of the plant that said `` stop risking Europe '' and called on French President Francois Hollande and German Chancellor Angela Merkel to commit to generating energy from alternative sources . Hollande has pledged to close the plant by the end of 2016 . CNN 's Elaine Ly , Sandrine Amiel , Boriana Milanova and Marie-Louise Gumuchian contributed to this report .
Environmental activists waved banner at nuclear plant . The plant 's operations were not affected , officials said . The Fessenheim plant opened in 1977 .