PARIS — A steam blast at France's oldest nuclear plant Wednesday left two workers with slight hand burns and revived calls to reduce the country's heavy reliance on nuclear power.

Nuclear safety authorities said there was no threat of radioactive leaks and that the incident at the Fessenheim plant in eastern France appeared minor. It touched a nerve, however, because anti-nuclear activists have long urged the closure of the plant. Those calls have mounted since the disaster at Japan's Fukushima Dai-ichi nuclear plant last year.

Utility giant Electricite de France, which operates the plant, denied initial reports of a fire. EDF said in a statement that the incident occurred during routine maintenance and that smoke was released. It said two workers suffered slight burns on their hands after oxygenated water escaped during maintenance, and the workers received immediate medical treatment. All nine workers at the site were examined, it said.

France relies on nuclear energy more than any other nation, getting about ¾ of its electricity from atomic reactors scattered around the country.

Workers were treating materials in an annex of the plant, not the building that houses the reactor, when the incident occurred, said Thierry Charles, deputy director of the Institute for Radioactive Protection and Nuclear Security. He said they were preparing a chemical solution for cleaning purposes, and there was an unexpected chemical reaction that resulted in a burst of oxygenated water escaping.

"It has nothing to do with radioactivity," he said, noting that oxygenated water is widely used for industrial purposes. He said at this stage he sees "no risks" resulting from the incident.

Noel Mamere, a parliament member from the environmental party and a vocal critic of nuclear energy, told BFM television that this incident is a reminder that "we must leave nuclear energy progressively" and turn to other, more renewable forms of energy.

The environment minister, Delphine Batho, said there was no immediate safety risk but ordered EDF and nuclear safety authorities to study what happened and submit a report to the government.