Just after 6 a.m. on Dec. 5, under cover of darkness, nine Greenpeace activists cut through a fence at the Nogent-sur-Seine atomic plant 95 kilometers (59 miles) southeast of Paris and headed for a domed reactor building. They scaled the roof and unfurled a Safe Nuclear Doesn't Exist" banner before attracting the attention of security guards. Two remained at large for four hours. On the same day, two more campaigners breached the perimeter of the Cruas-Meysse plant on the Rhone, escaping detection for more than 14 hours while posting videos of their sit-in on the Internet. The security lapses ... come at a time when debate has intensified on France's reliance on atomic power for three-quarters of its energy needs in the run-up to next year's presidential elections. They also preempt next month's release of the results of safety checks at France's 58 reactors, commissioned in the aftermath of the Fukushima tragedy. Greenpeace said its activists exposed the biggest security lapse to date at the reactors that are operated by Electricite de France SA.