France must immediately improve safety at its nuclear power plants so they can deal with natural disasters in the wake of Japan's Fukushima accident, an industry body said Thursday.

"The Fukushima accident and extra safety tests show the need to improve without delay some of the facilities' security parameters," the Institute for Radiological Protection and Nuclear Safety (IRSN) said in a 500-page report.

In the wake of the earthquake and tsunami that sparked a disaster at Japan's Fukushima plant in March, France, proportionally the world's biggest user of nuclear power, conducted tests on its own nuclear power plants.

Inspectors assessed the power plants' ability to resist natural catastrophes such as earthquakes and floods.

"It turns out that there are a certain number of non-conformities concerning nuclear safety frames of reference," IRSN chief Jacques Repussard told journalists.

The IRSN cited as an example inadequate emergency water reserves for cooling mechanisms or certain sections of piping that would not withstand an earthquake.

"These are little faults that could have serious consequences," Repussard said, nevertheless stressing there are "no dangerous nuclear sites in France".

"Installations authorised to be used in France can legitimately be considered as safe," the report said.

The IRSN said a next generation power station being built at Flamanville in the northwest was "better protected" against shocks such as an earthquake or flooding as its design "benefits from extra measures."

But power stations at Gravelines, Saint Alban and Tricastin must "take into account dangerous phenomena" as they are near industrial installations such as chemical factories or routes where explosives are transported, the IRSN said.