* Greenpeace enters nuclear site, drops smoke flare
* Intrusion just days before presidential runoff
* France's high use of nuclear is issue in campaign
* Man entered Civaux plant's security zone (Adds separate intrusion, details)
PARIS, May 2 (Reuters) - A Greenpeace activist dropped a smoke flare as he flew over a French nuclear reactor on a paraglider on Wednesday, seeking to draw attention to what green activists call gaps in nuclear security four days before a presidential election runoff.
The plant's owner, EDF, confirmed an engine-powered paraglider had landed within its Bugey nuclear site in southeastern France.
The pilot flew over the plant and threw a red-smoke flare on the roof of a building before landing, television images showed.
"At no moment was the safety of the installations at risk," EDF said in a statement, adding that the pilot was caught by the police in charge of protecting the site.
Separately, another man entered the Civaux nuclear site in southwestern France through the truck gate and remained hidden for an hour in a thicket in the "surveillance zone" before being arrested, EDF said.
France's dependence on nuclear energy has been much debated ahead of the vote. France is more dependent on nuclear energy than any other country, relying on it to produce 75 percent of its electricity.
"This overflight shows the vulnerability of the French nuclear site to an air attack," Sophia Majnoni d'Intignano, in charge of nuclear questions at Greenpeace, said in a statement.
"While Germany took account of a plane crash in its safety tests, France still refuses to analyse this risk for our reactors."
Similarly, in December, Greenpeace activists entered the Nogent-sur-Seine plant near Paris, climbing onto one of the domes that houses a reactor, while other activists entered other nuclear installations.
Socialist presidential candidate Francois Hollande has said he would shut France's oldest nuclear plant if elected.
After the Fukushima disaster in March 2011, France along with other European countries, pledged to carry out safety tests on its 58 nuclear reactors to test their capacity to resist flooding, earthquakes, power outages, failure of the cooling systems and operational management of accidents.
But those did not include terrorist attacks, or the possibility of a plane crash. (Reporting by Thierry Leveque and Sybille de La Hamaide, additional reporting by Marion Douet, editing by Maria Golovnina)