The Nuclear Safety Authority declared the accident "terminated" soon after the blast at a furnace in the Centraco site, in the southern Languedoc-Roussillon region, about 20 miles (32 kilometres) from the city of Avignon. One of the injured suffered severe burns.
The agency said the situation had been brought under control in less than an hour after it broke out shortly past noon. The building that houses the furnace wasn't damaged, no leaks were reported and residents who live near the site were not evacuated, the agency said in a statement.
The cause of the accident is not known, and an investigation has been opened to see what went wrong, authorities here said.
France is the world's most nuclear-dependent nation. It relies on the 58 nuclear power plants that dot the country for about three-quarters of its total electricity, and it's also a major exporter of nuclear technology throughout the world.
While the March meltdown at Japan's Fukushima plant prompted other countries to re-evaluate their nuclear programs — with neighbouring Germany vowing to shut all its plants by 2022 — France has remained steadfast in its support for nuclear energy.
Authorities here downplayed the importance of Monday's incident.
"It's an industrial accident and not a nuclear accident," Industry Minister Eric Besson said on i-Tele television. "There have been no radioactive leaks and there have been no chemical leaks."
Still, French environmentalists have long called for an end to the country's nuclear program, and several ecology and leftist parties urged authorities here to rethink nuclear policy after Monday's incident.
Sophia Majnoni, who runs Greenpeace's nuclear campaign in France, noted that the plant was not part of a French safety audit conducted in the wake of the Fukushima accident.
"It is a nuclear plant yet its resistance to earthquake or flooding won't be checked, which allows us to think that the government has not drawn all the lessons from the Fukushima catastrophe," she said. "It is not only the nuclear power plants that are dangerous for population."
Ecology Minister Nathalie Kosciusko-Morizet was slated to visit Centraco — one of four industrial installations at the Marcoule nuclear site — later Monday. The 300-hectare (740-acre) Marcoule site also houses a research centre and four industrial sites, including one that makes Mox, a fuel made from plutonium and uranium.
France's EDF electric power company, whose subsidiary operates Centraco, said the furnace in Monday's accident is used to melt slightly radioactive metal waste, including gates, pumps and tools into easy-to-store bars.
The furnace went into service in 1999, EDF said, and treats mostly waste from EDF's own power plants, as well as a small amount of material from hospitals or medical research labs. Nothing comes from weapons manufacture, company spokeswoman Carole Trivi said.
The person killed was a foundry worker who was near the furnace when it exploded. The prognosis for the seriously injured worker, evacuated to a hospital in nearby Montpellier, was not immediately known.
None of those involved in the accident were exposed to radiation, the nuclear safety agency said.
The head of the Vienna-based International Atomic Energy Agency, Yukiya Amano, said his organization's "incident and emergency centre was immediately activated and has sent requests for detailed information."
Nuclear power is big business in France. EDF and state-owned nuclear giant Areva have built reactors the world over and inked recent deals to build Poland's first nuclear plant and to create a joint-venture with a Chinese nuclear company. France also treats nuclear waste from around the globe.Japan's March 11 tsunami and the disaster at the Fukushima nuclear plant didn't spark the kind of soul-searching over reliance on nuclear energy in France that it did in other countries, including neighbouring Germany. There, eight older reactors were quickly taken off the grid, and the nine remaining plants are to close over the coming decade.
France's President Nicolas Sarkozy appeared to dig in his heels in the wake of the Japanese meltdown, pledging as recently as June to stick to a plan to invest €1 billion ($1.37 billion) in future nuclear reactors.
James Acton, an expert in nuclear policy at the Carnegie Endowment for International Peace, said that — provided the information from French authorities was correct — the accident appeared not to be very serious
Acton said the biggest concern in the coming hours will be to monitor whether any radiation is released. That will depend in large part on where exactly the furnace is on the site and how well contained it is.
If EDF's assurances that no radiation has escaped so far and that the building around the furnace is intact prove correct, Acton said it would be considered "an industrial accident that happened to contain radioactive material" — and far less serious than an accident involving nuclear fuel.
Asked whether he thought the Monday's accident could sway public opinion in France, Acton said it was "unlikely."
"French public opinion has been robust to date about nuclear," he said. He also noted that even without nuclear power, waste treatment facilities like the one at Centraco would still need to exist to handle medical waste and other sources of radioactivity.
Associated Press writers Sarah DiLorenzo and Cecile Brisson in Paris contributed to this report.