France needs to upgrade the protection of vital functions in all its nuclear reactors to avoid a disaster in the event of a natural calamity, the head of its nuclear safety agency said, adding there was no need to close any plants.

After Japan's Fukushima disaster in March, France along other European countries decided to carry out safety tests on the country's 58 reactors and its next-generation reactor under construction in northwestern France.

The aim was to test their capacity to resist flooding, earthquakes, power outages, failure of the cooling systems and operational management of accidents.    

IRSN, experts on radiation protection and nuclear safety, delivered a 500-page report to nuclear watchdog ASN on Thursday, which will in turn hand over its conclusions, based on the report, to the government at the end of 2011.

"There is a need to add a layer to protect safety mechanisms in reactors that are vital for the protection of the reactor such as cooling functions and electric powering," Jacques Repussard, head of the IRSN, told Reuters in an interview.     

"For example, it is necessary that each reactor has at least one protected independent diesel generator positioned out of the way which does not fail even in case of an extremely violent earthquake," he said.     

"All reactors have to survive much more violent events than what they were built to resist," he added, citing as possible examples an earthquake that destroys the southern city of Nice or the collapse of all dams at once, triggering massive floods.

France's oldest reactors were built in sets of two so that in case of a problem with one reactor, the resources of the second one, such as personnel and equipment, could be used. "It was never envisaged that there could be a simultaneous problem in two reactors," he said.

Repussard said he could not tell how much the upgrades would cost EDF, which operates all of France's reactors, and how long they would take. - Reuters