An accidental spillage of waste containing uranium occured Tuesday at one of France's top nuclear plants but authorities said there was no immediate cause for concern, authorities said.

Some 30 cubic metres (over 1,000 cubic feet) of effluents containing 12 grammes (easily less than half an ounce) of uranium per litre spilled out at the Tricastin Nuclear Power Centre in Bollene in southern France.

The nuclear centre groups a collection of sites run by nuclear giant Areva and power utility EDF spread across four different communes.

"This is the first time that such an incident has occurred," Gilles Salgas, communications officer for Socatri, an Areva affiliate, told AFP. The unit has been functioning since 1975.

The spillage occurred when a tank was being cleaned.

Immediate security measures were taken.

"The uranium content in the surface water (which is not intended for human consumption) was much higher than normal but greatly reduced due to dilution throughout the day," a statement said.

The Commission for Independent Research and Information on Radioactivity chief Corinne Castanier said: "The health risk is negligible but this incident follows similar ones and shows up weaknesses in the way waste is handled."