France's nuclear watchdog has called on the country's 58 power plants to make safety improvements quickly, almost 10 months after the Fukushima disaster.
But it says none of the reactors needs to be shut down, following stress tests carried out in the wake of the Japanese earthquake and tsunami.
The watchdog estimates the changes would cost tens of billions of euros.
France obtains 75% of its electricity from nuclear power and the industry's future has become a political issue.
The opposition Socialists want to reduce the country's reliance on nuclear power and have agreed to phase out 24 reactors as part of a pact criticised by the ruling UMP party ahead of presidential elections.
The Nuclear Safety Authority (ASN) says industry operators must come forward by 30 June with measures they would take in response to floods and earthquakes, "preventing a serious accident or limiting its spread" and "limiting massive [radioactive] releases".
It also proposes the establishment by 2014 of a rapid reaction force that would take charge within 24 hours of a nuclear accident taking place.
ASN President Andre-Claude Lacoste said the work and funding for the proposals was "quite massive" and would involve the recruitment of hundreds of people.
The French government asked the watchdog to investigate the safety of the country's nuclear plants in March 2011. ASN's conclusions were based on a report by experts last November that decided the reactors were safe but that some were vulnerable to external factors such as earthquakes or floods.