Under French labor laws, staff have the right to walk off the job if they consider there is a clear and imminent threat to their health or safety.

After working in the radioactive areas of nuclear plants, staff have to step through narrow shower-style portals in their underwear to be checked for possible radiation exposure. Workers feared the surface areas of these portals could become a source of spreading the virus.

EDF has now agreed to clean the portals twice per eight-hour shift, to increase security distances between workers and provide gloves and hand sanitizer, according to new internal rules announced on Tuesday.

"The problem has been solved or will be soon, provided that guidelines are respected," CGT union member Thierry Raymond told Reuters.

CGT nuclear specialist Thomas Plancot said more than a dozen workers - mostly contractors - had walked out over the issue in the nuclear plants of Fessenheim, Civaux and Chooz, including a sixty-year-old who considered himself especially at risk because of his age.

An industrial source said lower on-site staffing numbers in the nuclear plants would have no impact on output or security and that with more people working from home it was easier for on-site staff to keep their distance from one another.

France on Monday ordered nationwide confinement of residents and asked companies to organize homeworking as much as possible.

An EDF spokesman said the 40 nuclear reactors currently operating were not impacted by the coronavirus crisis.

EDF, which has declined to comment about the level of absenteeism or the number of confirmed coronavirus infections among its staff, said its nuclear plants could operate for three months with a 25% reduction in staffing levels and for two to three weeks with 40% fewer staff.

For now, only staff involved with operation, maintenance and security are working on-site in EDF's nuclear plants.

"Even under our most pessimistic assumptions, we think we will be able to produce enough electricity for the entire country at all times," EDF chief executive Jean-Bernard Levy said on Europe 1 radio on Friday.

By Benjamin Mallet