* At least 11 reactors affected
* Electricity imports jump
* EDF says 10 percent of staff participating (Recasts, adds EDF comment, power imports)
PARIS, May 26 (Reuters) - Nuclear power plants across France were hit with unplanned outages on Thursday after unionised workers at utility EDF joined a rolling nationwide strike against planned government reforms.
At least 11 of France's 58 reactors suffered outages, according to grid operator RTE, lowering output by about 5 gigawatts (GW) or 6 percent of the country's nuclear capacity.
Members of the CGT union at all 19 of France's nuclear power stations voted on Wednesday to join the strike which has already paralysed businesses and disrupted fuel supplies causing shortages in some places.
State-controlled EDF is required to maintain a minimum output level so as to prevent power cuts during any strike action and the public may not notice the lower nuclear power output.
However, the fall does mean higher costs for EDF as it must start up more expensive coal- and gas-fired power plants and boost electricity imports.
France's power imports, mostly from Germany and Switzerland, had by 1100 GMT jumped to about 3.3 GW from approximately 800 MW around the same time a day earlier, RTE data showed.
Nearly 10 percent of EDF's staff were participating in the strike, a company spokeswoman said, declining to comment on output except to say the utility continued to supply its clients. (Reporting by Bate Felix; editing by Jane Merriman and Jason Neely)