Fire alarms were set off at France's Feissenheim nuclear power plant when a blast of steam erupted after an accidental chemical reaction, injuring at least two people.
Initial reports said that a fire had broken out in the plant, but EDF, the power supplier which operates the plant, said they were unfounded.
The blast of steam was apparently produced by the reaction of hydrogen peroxide with water in the reactor's reservoir, which local officials said was quickly brought under control.
The Feissenheim plant, located in the northeastern province of Alsace near the border with Germany, was opened in 1978 and is currently France's oldest plant in operation.
Since it was built, the plant has been the target of nuclear power opponents, particularly after the recent meltdown at Japan's Fukushima nuclear plant last year.