An explosion at a nuclear waste-management site at the Marcoule complex in southeastern France on Monday has killed at least one man, but safety officials say there was no leak of radioactive material at one of the country's oldest nuclear facilities. 

Four people were also injured in the explosion, which occurred around 12:37 p.m. local time. One person was badly burned and has been airlifted to a hospital in Montpellier, while three others were taken to a local hospital, according to reports.

No names have been released, and the incident is being described as an "industrial" rather than nuclear accident.

What is at the site

The sprawling Marcoule nuclear site has been around since the 1950s and includes research facilities as well as a waste disposal service run by Centraco, which is on the grounds and is where the explosion took place.

Marcoule also produces a fuel called MOX, which is made from weapons-grade plutonium. The fuel can then be used in commercial nuclear reactors.

Two reprocessing sites in France, La Hague and Marcoule, "contain over 90 per cent of France’s radioactive waste inventory. Their inventories include spent fuel, separated plutonium, large quantities of liquid and vitrified high-level waste, and various types of intermediate, transuranic and low-level radioactive wastes," according to the International Panel of Fissile Materials.

The fuel production and the waste disposal techniques are controversial, and a number of environmental groups have lined up against them, saying the plants that process the highly radioactive material are dangerous places that release too much radioactivity.

The Agency for Nuclear Safety (ANS) said the explosion was set off by a fire near a furnace at the Centraco facility, a centre for processing and conditioning low-level radioactive waste that is situated at the massive Marcoule complex.

The accident was under control within the hour, the agency said in a statement.

"According to initial information, the explosion happened in an oven used to melt radioactive metallic waste of little and very little radioactivity," the statement said. "There have been no leaks outside of the site."

The Marcoule site does not house any nuclear power reactors.

Marcoule is located in the Gard region of France, in Languedoc-Roussillon, near the Mediterranean Sea.

No evacuation notice was given to the local area but a security perimeter around the site has been established, according to reports.

Marcoule opened in 1950s

Marcoule is owned by French power utility EDF and is adjacent to a nuclear research centre.

The reason for the blast wasn't immediately clear, but officials said it was contained within the furnace area. An investigation has also been opened.

"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."

The International Atomic Energy Agency (IAEA) has contacted French authorities to learn more about how the explosion may have happened.

"We are working on this issue," IAEA director general Yukiya Amano told a news conference in Vienna during a weeklong meeting of the IAEA's 35-nation governing board.

The IAEA's board is expected to approve a plan to strengthen global nuclear safety following the Fukushima nuclear disaster in Japan. But French environmentalists seized on the occasion to point out that Marcoule was not included in a French safety audit conducted in the wake of the Fukushima crisis.  

The European Commission said in a statement it would help French authorities assess the impact of the Marcoule explosion, and monitor it closely. 

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Rescue services workers move out a person injured in the explosion at the Centraco facility at the French nuclear waste treatment site of Marcoule on Monday. ((Reuters))

Those injured in the accident were not contaminated with radiation, and the outside of the building that houses the oven showed no sign of damage or contamination, the ANS said in a separate statement.

Officials from EDF, whose subsidiary operates Centraco, stressed that no waste treated at the site of the explosion came from a reactor.

Marcoule opened in the 1950s and is one of the oldest nuclear sites in France, the world's most nuclear-dependent nation, relying on nuclear energy for more than two-thirds of its energy needs.

Reactors put through stress tests

France's 58 nuclear reactors have been put through stress tests since the March disaster at the Fukushima nuclear plant in Japan that was linked to an earthquake and tsunami. Other EU members are also conducting tests on their nuclear facilities.

It's not the first controversy involving Marcoule, according to the International Panel on Fissile Materials (IPFM).

Languedoc-Roussillon , France

Some liquid waste at the site was, until 1998, stored in carbon steel drums that began to corrode, said the group in a 2008 report.

"The carbon steel drums are therefore being placed inside stainless steel over-packs. As of the end of 2005, over 5,000 carbon steel drums had been overpacked," the report said.

And, according to the French Court of Accounts, as many as 61,597 drums required reconditioning, it added.

The group quoted in its report the French Court of Accounts as saying: "The circumstances of this reconditioning are complicated by the ignorance of the operator of the exact content of the drums produced prior to 1995 and therefore the level of radioactivity: it is one of the stunning facts from a time when nuclear safety was not at the centre of preoccupations."

The IPFM said that in 1967 and 1969, "46,396 waste barrels were dumped into the sea off the coasts of Spain and Brittany," including 3,479 from the liquid waste treatment facility at Marcoule.

The exact radioactivity of the low-level liquid waste is "highly uncertain because of uncertainties in the accounting and inventorying of radioactive waste on the Marcoule site," said the IPFM.

James Acton, an expert in nuclear policy at the Carnegie Endowment for International Peace, said that if the information  from officials is accurate, the Marcoule accident does not appear to be serious. Monitoring whether any radiation is released will be a top priority for the next few hours, he said, adding it's still "unlikely" Monday's incident will turn the French public off nuclear power.

With files from The Associated Press, BBC