A French nuclear watchdog on Tuesday called for the country's plants to beef up safety to cope with natural disasters under a programme likely to cost tens of billions of euros (dollars), but said none faced any immediate shutdown.
It also called for a "rapid reaction force" to be operational by the end of 2014 that could intervene in a nuclear accident in less than 24 hours.
The recommendations, handed to Prime Minister Francois Fillon, were drafted by the Nuclear Safety Authority (ASN) as part of a post-Fukushima inspection of France's nuclear industry.
"Following additional safety evaluations of priority nuclear installations, the ASN believes that the installations that have been assessed have a sufficient level of safety to warrant it not to request any immediate shutdown," it said.
"At the same time, the ASN believes that continuing operations require existing safety margins to be strengthened as swiftly as possible."
It gave operators until June 30 to spell out measures to strengthen safety in response to floods and earthquakes, providing for instance backup systems for power, coolant and plant operations.
The measures should aim at "preventing a serious accident or limiting its spread" and "limiting massive releases (of radioactivity) in an accident scenario," the ASN said.
In addition, operators should itemise their procedures for handling a crisis.
The measures will require "tens of billions of euros (dollars) in investment," the ASN's president, Andre-Claude Lacoste, told a press conference.
"The work and financing are on a massive scale, requiring the hiring and training of hundreds of people," Lacoste said.
He noted that a single emergency diesel generator, designed to be protected against floods, costs "tens of millions" of euros. Another major expense would be building "bunkers" to serve as emergency backup for plant controllers.
"I don't see how this cannot have an impact on (electricity) prices," he warned.
Fillon's office said the government would ensure that the requests would be carried out "in their entirety (and) on time."
An anti-nuclear group, the Nuclear Observatory, dismissed the ASN report as a "predictable trick."
"The ASN is absolutely not independent and plays the role allotted to it by the government -- to have the public believe in the feasibility of nuclear safety," it said.
France is the most nuclear-dependent country in the world, deriving 75 percent of its electricity needs from 58 reactors, most of which were built in response to the oil shocks of the 1970s.
The programme gave birth to a massive state industry, with giants such as the nuclear plant builder Areva and operator Electricite de France (EdF) as well as the Atomic Energy Commission (CEA), which carries out civilian and military research.
But a decades-long "nuclear consensus" gathering all the major parties was badly shaken by the March 11 earthquake that ravaged the Fukushima Daiichi plant in northeastern Japan.
The issue is rising up the political agenda ahead of key elections this year.
In November, the opposition Socialist Party joined with the Greens to campaign for France to scale back its reliance on nuclear to 50 percent by 2025 by shutting 24 reactors and boosting production from wind, solar and other renewable sources.
French President Nicolas Sarkozy, like his predecessors, is a champion of nuclear. He lashed the Socialist-Greens proposal as "irresponsible" and potentially crippling.
France will vote in the first round of a presidential election in April and potentially a second round in May, followed by a two-round parliamentary election in June.
Explore further: Should Australia consider thorium nuclear power?