Strikes by workers reduced nuclear power generation by 3.3 gigawatts (GW) by 0653 GMT Thursday plus 410 megawatts (MW) at hydropower stations, data from power group EDF showed.
Five reactors were affected due to the strike, while the disruption represented about 8.5% of total production on Thursday morning, the data showed.
France is currently a net power importer of near 7.4 GW, while nuclear production is around 26.5 GW, grid operator RTE data showed.
The 1.3 GW Nogent 1 reactor is shown as offline due to the strike. The reactor also went offline on Wednesday with an unplanned outage following a water supply regulation failure in a cooling circuit in the non-nuclear part of the facility. (Reporting by Forrest Crellin; Editing by Alison Williams)